The Wait For Concrete to Dry

 A building project is typically handled in a series of stages, each of which has its own manager. The goal is always to smoothly hand off each segment of a construction project from one manager to the next without any delays. But when moisture-sensitive flooring is involved, there’s one part of construction that can throw a wrench in the process: The concrete slab.

What’s Required to Achieve Successful Flooring Installation?

For flooring installation to be successful: The slab moisture content and pH levels need to be within optimal range;

The slab must be protected from external moisture;

Compatibility of the moisture level in the slab with both the specified floor covering and flooring adhesive needs to be achieved

Moisture-emission potential must be addressed.

What are the Factors That Delay a Slab’s Drying Time?

 

The procedures involved with pouring and drying a concrete slab are guided by many industry standards. But the drying time for each slab is almost impossible to predict. The factors which contribute to the slab’s drying time are unique to each and every installation. The drying time variables include:

The components of the original concrete mixture (water/cement ratio)

Ambient air humidity

Final service conditions

Surface finishes

Functionality of the HVAC system

Floating practices or rewetting

When any of the above-named factors are altered during the project, the concrete may require a longer drying time. Delays to achieving a properly dried slab can throw off entire construction schedules.

 

Is it Better to Wait for the Slab to Dry or Forge Ahead?

Lost man hours and additional costs are just two results of scheduling interruptions on a construction project. But the alternative, which is to push ahead in spite of the slab’s condition, leads to flooring failure. Ultimately, a moisture-related flooring problem is a no-win situation for everyone from the contractors and construction managers to the flooring installers, adhesive manufacturers, and facility owners. Experience has proven, that the results of forging ahead on the installation of flooring before the concrete moisture issues in the slab have been resolved , carries a much larger price tag than playing the waiting game and getting it right in the first place.

 

All Eyes on the Goal, Not the Clock

The ultimate goal in a construction project to end up with an installed flooring system that’s problem-free for the long term. When the construction schedule leaves no room for moisture issues in the concrete to be properly dealt with, there’s a temptation to rush the project and invite flooring failure.

How To Know When the Slab is Ready There are different methods which can help to speed along the drying time of the slab, such as desiccant drying

and surface treatments. But how can the flooring contractor be certain that the moisture levels in the slab are compatible with the moisture-sensitive adhesive and flooring to be installed on the project? An accurate monitoring of the relative humidity (RH) within the concrete slab is the best way to determine when the drying time has been completed. Surface testing only of moisture conditions of a concrete slab, such as calcium chloride testing, aren’t reliable, in spite of the fact that such methods have been commonly used in the industry for years. RH testing is superior to surface-only testing in that it reflects the final RH conditions underneath an installed floor. Supplied with accurate knowledge of a slab’s RH condition, the general contractor and flooring installer will know whether to allow for more drying time to reach adhesive/flooring specifications or to choose a different flooring adhesive or flooring product which is compatible with the slab’s current conditions. RH testing is a great benefit to the construction process, giving everyone involved the information they need to understand that it’s time to either wait or move on to the flooring installation phase of the project.

Concrete Prep

Installation success only happens with thorough subfloor and job preparation. Skipping a moisture test, not removing concrete curing or sealing compounds, not removing old adhesives, or not leveling a subfloor are easy steps to a costly job failure. Burnished or hard trowel finished concrete is a large and growing problem that we are receiving from the concrete industry. With the use of power trowels the concrete finishers are over-troweling the concrete surface, leaving a burnished surface. Burnished or hard troweled concrete is shiny and highly consolidated and presents several problems for the flooring industry. First, the highly consolidated surface severely slows the drying of the slab because the moisture is slow to pass through the consolidated layer. Second, moisture testing that is done at the surface (Calcium Chloride) will yield low readings or false positives due to the retarded moisture vapor flow and the short period of time the test is run. Third, some adhesives, especially epoxies and urethanes, will not be able to achieve a good mechanical bond to the concrete’s surface. These types of adhesives are designed for excessive abuse and require an open slab’s surface to attain this mechanical bond. Concrete curing or sealing compounds – ASTM F-710 states that if a curing, sealing or parting compound is to be used it should be removed. Problems begin as many flooring contractors do not realize that sanding with a buffer will not remove the compound. Sanding will only scratch the curing, sealing or parting compound. Other installers believe that curing or sealing compounds will either walk-off or degrade from either UV exposure or oxidation. While this is somewhat true, the exposure does nothing to the pores of the concrete that is filled by this same compound. These compounds also slow the migration of moisture and retard drying. This is another reason why surface moisture tests must be ground to open the pores of the concrete’s surface. Going directly over a curing or sealing compound is foolish. There have been situations where the residual solvent in a heavily applied cure ‘n seal attacked the applied adhesive about nine months after the installation. Buffing or sanding the surface of the concrete – Installers will give a concrete slab a quick sanding with an 16 or 24 grit open coat sandpaper, thinking they have taken care of anything that might prevent a good bond. On the contrary, sometimes scratching a latent substance that is present on the surface of the concrete will only allow it to de-bond faster from the concrete surface. Situations like these de-bond sometime after the slab is in use and the flooring has been installed. Poorly finished concrete – Poorly finished concrete is generally dusty and very absorptive. Dust will cause the adhesive to ball-up and also to dry too fast. Usually, concrete like this will require a primer to slow the absorption and drying time. Latent substances on the concrete surface – Many times in new construction a lot of mud can be tracked onto the concrete surface. If the mud is clay-like or high in fines it can stick to the surface like it is part of the concrete. A solution for this would be to use a buffer sander to remove this laitance, or a layer of weak powdery material on the surface. Concrete mitigation treatments – Many contractors are automatically planning for moisture treatments from past experiences with moisture. When an installer arrives at the jobsite, make sure he is aware if the slab has been treated for moisture. Otherwise he may disturb the ongoing mitigation treatment. The installer also needs to be aware of is if the slab is non-porous and needs to be treated as such. Other factors the installer should be aware of include whether the job will feature a specialty flooring or specialty adhesive
that needs to be installed over a non-porous substrate. Concrete to have epoxy applied – Some slabs are either going to have an epoxy adhesive used under a resilient flooring product or have an epoxy coating applied. In either of these situations it is necessary to be able to achieve a good mechanical bond between the adhesive and the substrate. Choosing the correct CSP profile – When should you abrade the concrete surface? For proper bonding of concrete overlays and coatings, it’s important to give the surface the correct concrete surface profile, or CSP. To help contractors make this assessment, the International Concrete Repair Institute (ICRI) has developed benchmark guidelines for CSP—a measure of the average distance from the peaks of the surface to the valleys. They range from CSP 1 (nearly flat) to CSP 9 (very rough). As a general rule, the thicker the overlay or topping, the more aggressive the profile needs to be. A skim coat, for example, may require a light CSP of 2 to 4. For thicker self-leveling or polymer overlays, acceptable profiles generally range from CSP 4 to 6. Achieving surface profiles in the higher ranges often requires roughening by shot-blasting or scarifying. With existing adhesives, the majority of the adhesive must be scraped to a thin residue before shot-blasting to prevent the shot from gumming up or bouncing off the surface of the adhesive. Please note to make sure the existing adhesive does not contain asbestos. Asbestos was used in the Black Cutback Adhesives up until around 1983. Do not use adhesive/mastic removers. The purpose of surface preparation is to provide sound, clean and suitably roughened surfaces on concrete substrates. This process includes the removal of unsound concrete and bond-inhibiting films, strength verification, opening the pore structure and establishing profiles suitable for the application of the specified flooring system.

Resilient Concerns

 

I am sure you have heard “The new floor is only as good as what you cover,” and that is certainly the case. Here are problems that can cause a lot of resilient floors to fail.

 

Concrete; Failures that are moisture or pH related continue to be a problem. Testing can detect elevated moisture conditions before they become problems and it can also be another source of income for the professional installer who knows how to do the testing properly. ASTM F 1869 (Calcium Chloride Test) is a test for vapor emissions from the concrete surface and ASTM F 2170 (Relative Humidity Probe method) measures moisture inside the slab. There is no correlation between these two tests. Both provide valuable information about the condition of the concrete. There is a growing awareness of these test methods so it pays installers to learn what testing methods are out there and how to do them.

Patching Compounds; Over watering is the number one cause of patching compound failure. Today’s patches are modified with polymers that give them tremendous strength and bonding power, but the chemistry of these products is compromised if too much water is added to the mix. The finished patch layer will be weaker, not as hard and more porous – three characteristics that can adversely affect the floor covering or the adhesive. Another cause of patching compound failure is applying it in too thick a layer so that cracks or it is not dry when the floor is installed. Check the manufacturer’s specs for how thick the patch can go down because most of them can’t go much over 1/2″ in a single application. Finally, there is a big misunderstanding out there about skim coating in commercial applications directly over an existing floor like vinyl composition tile. Read the book – chances are the patching compound manufacturer does not recommend this procedure, although many dealers and installers think they do. The reason for this is due to rolling loads possibly breaking up the skim coat over the existing vinyl.

Adhesive Residue; In renovation work, failure to remove the old adhesive can cause problems such as indentation of the new flooring, chemical reactions between the old adhesive and the new adhesive, patch blowing off the floor or complete failure of the new adhesive. If you are just pulling up that old floor, skim coating and installing the new floor, your installations are a problem waiting to happen. Read the instructions and you’ll find that the patching compound manufacturer wants most, if not all of the old adhesive removed from the floor before the patching compound is applied. And, don’t use chemical adhesive remover to do the job because they can cause problems later on with the new adhesive. Use mechanical methods to remove the adhesive residue.

Plywood Underlayments; Today, the three most common panel underlayments are plywood, lauan, or fiber reinforced panels. Most resilient flooring manufacturers are no longer recommending lauan as an underlayment. Lauan tends to be soft and susceptible to denting and crushing under concentrated loads such as furniture legs or high heels. Many of these panels have caused severe problems such as discoloration, delaminating and adhesion failures. If you are using lauan, the flooring manufacturer may not cover any failures and the manufacturer of the panel will be nowhere to be found if you have a problem. Plywood is a superior product to Lauan. Real three-ply or five-ply 1/4-inch-thick underlayment products (like Ultraply XL) are readily available today from flooring supply distributors. These branded products come with instructions for how to install them and have a solid manufacturer’s warranty. Fiber reinforced panel underlayments are common in the stone and ceramic industry and are starting to gain popularity for resilient flooring as well. These products remind one of drywall in appearance and in their score and snap method of cutting, but they are designed to be underlayments so they carry the performance characteristics and warranties for use under resilient.

Adhesive Issues; Adhesive selection and adhesive use are often misunderstood in the process of specifying and installing resilient flooring. For example, although it’s tempting to save money and time, you can’t use clear thin spread to install solid vinyl tile. So, before the job is even quoted it is important to match the adhesive to

the job and quote the job accordingly. Once the adhesive is selected, proper application is critical. The trowel is an application device that puts adhesive on the floor and is also a measuring device that precisely meters the amount of adhesive being applied. Every manufacturer has specific trowel notch recommendations. One trowel for everything will not work for you. I have often seen the results of too much adhesive – sheet vinyl with indentations, tile with adhesive oozing between the joints, lumpy, bumpy cove base, stair treads that shifted because the excess adhesive didn’t dry, and epoxy that doesn’t cure. The idea that more is better is a huge mistake to make with resilient flooring products. The cost of a trowel is a tiny part of the installation cost. There is no excuse for not having the right trowel on the job.

 

Seams; There is an art to cutting and seaming products. Seams are what most end users and home owners fear. Today’s products are more flexible and easy to cut, but that does not make seaming technique any less critical. Some products are seamed by the double cut method and others by under scribe or straightedge and butt methods. Knowing the difference can make you or break you as far as the finished installation goes because different products have different cutting methods for making a seam. For example, cutting seams in natural linoleum is different than in vinyl or rubber sheet goods. It tends to shrink in length and grow in width, so linoleum seams are often cut slightly open on side seams and not on cross (end) seams. On the flip side, some of the flexible vinyl and rubber products today work best with a double cut seam and the traditional inlaids work best with recess scribing. In these cases, the seams will be net with no gaps. Where to cut the seam is an issue in the case of patterned materials with a grout line. Do you cut the seam in the middle of the grout line or on the edge? This will vary from product to product. Today’s fiberglass Loose-Lay floors require seams to be double-cut.

Pay attention to the details and refer to the manufacturer’s guidelines. Specialized tools are available for trimming sheet goods and cutting seams so make sure you are ready by having the right equipment. As far as seam sealers, I have seen a lot of split seam failures caused when the seam sealer applicator tip does not penetrate into the seam. This means that the sealer is left only on the surface rather than inside the seam holding the two pieces together. On the commercial side, failures in heat welded seams are often caused by leaving a gap when the flooring is installed so that the welded seam is not as strong as it would be if the two pieces are butted together before welding. Cutting too wide a groove, moving too fast with the welding gun, or having the wrong temperature on the gun are all causes of heat weld failures. Training is available from a number of manufacturers and there is always scrap material to practice on.

 

Maintenance; Maintenance related complaints are almost as frequent as installation complaints these days. I have found these problems are often the result of misunderstandings because of a lack of written instructions, or because someone who sold or installed the material gave the wrong advice. If you don’t know, don’t answer. If you give the wrong advice and something goes wrong with the floor, you could be held liable. For example, cleaning for no wax vinyl is often misunderstood. Soap based cleaners can leave a dulling film, where a mild detergent will not. Another example is real linoleum, where the use of strong alkaline cleaners can cause cracking, shrinking and possible discoloration. Yet another example is cork flooring, a resilient flooring material that acts a lot like wood. Using a lot of water on cork can ruin the floor. In all cases, how the floor is cleaned can cause permanent damage. The use of the wrong chemicals or the wrong cleaning or scrubbing pads can ruin the floor. The best advice to an installer as far as maintenance is, if you don’t know, don’t tell. Somewhere in the manufacturer’s material you bring to the job will be a phone number or website address. Find it and give it to the customer. This is one good time to “pass the buck” to the manufacturer, or back to the dealer so the maintenance is done correctly.

Proper Installation of Solid Hardwood Flooring

 Most all wood floors will have an occasional squeak, pop, or creak. This is considered an acceptable condition that does not make the floor fail to perform. But like a lot of things that go into homebuilding, it’s often the things that the homebuyer doesn’t see that really count. And this is particularly true when it comes to fastening wood floors. It takes the right combination of materials, tools and techniques to properly install a wood floor. Done right, the homebuyer notices only the beauty of the floor itself. Done wrong, the problems stick out like a sore thumb: creaks, pops, moving boards, uneven boards and ugly nail holes. You only have one chance to get it right. So, use care and attention to detail, along with the right materials, tools and techniques, and you’ll win every time.

The subflooring itself can contribute to noises. Particle board is well known for fastener movement and resulting squeaks. Some OSB products have shown low fastener retention as well. When coupled with typical moisture events during construction, OSB subflooring is at risk for producing noises related to moisture-induced thickness swell associated with reduced density and irregular flatness. Plywood on the other hand may show some delamination which affects fastener holding.

 

Since wood flooring is normally placed in homes that are not designed to meet the bare minimum subfloor performance requirements, a system that exceeds the minimum is recommended by NWFA. The APA has a recommended system called a Code Plus System that shows the use of thicker panels, a step above the minimum performance rating. A subfloor system should be sufficiently stiff to allow minimum movement.

 

The NWFA recommends the following for acceptable subfloor/truss systems;

 

1. On truss/joist spacing of 16″ o/c or less, the industry standard for single-panel subflooring is nominal 5/8″ CD Exposure 1 Plywood subfloor panels (CD EXPOSURE 1) or 23/32″ OSB Exposure 1 subfloor panels, 4′ X 8′ sheets.

 

2. On truss/joist spacing of more than 16″, up to 19.2″ o/c, the standard is nominal 3/4″ (23/32″ T&G CD EXPOSURE 1) Plywood subfloor panels, (Exposure 1), 4’ X 8′ sheets, glued and mechanically fastened, or nominal 3/4″ (23/32″) OSB Exposure 1 subfloor panels, 4’ x 8’ sheets, glued and mechanically fastened.

 

3. Truss/joist systems spaced over more than 19.2″ o/c up to a maximum of 24″ require nominal 7/8″ T&G CD EXPOSURE 1 Plywood subfloor panels, (Exposure 1), 4’ X 8′ sheets, glued and mechanically fastened, or nominal 1″ OSB Exposure 1 subfloor panels, 4’ x 8’ sheets, glued and mechanically fastened — or two layers of subflooring. Or brace between truss/joists in accordance with the truss/joist manufacturer’s recommendations and with local building codes. Some truss/joist systems cannot be cross-braced and still maintain stability.

 

The reason for the thicker requirement for OSB is that tests have shown the thicker 3/4″ (23/32″) OSB holds wood flooring fasteners only as well as 5/8″plywood. Better nail holding produces a quieter floor with less movement among boards. Less movement among boards for site finished flooring also produces less finish separation or flaking along board edges.

 

We hear the term, L/360, as the term for the greatest allowable deflection at center span. This means that for a span of 20 feet, the deflection can be just over 5/8″ at center span. Today in order to accommodate the wide-open areas in homes, these and longer spans are typical, thus significant deflection can occur along the length of joists. For less deflection a stiffer joist system is needed, such as L/480 or L/560 and greater. In addition, wider spacing than the traditional 16″ On Center between supporting joists allows for even more variation.

These systems all pass building codes and support the intended loads; however, with hardwood flooring the

expected performance may not be achieved with maximum joist spacing, maximum spans, and minimum thickness subflooring.

The stiffer systems are also generally also recommended for engineered flooring, since these products are normally thinner and add minimally to the strength of the system. Manufacturers have specific subfloor specifications, so always follow the manufacturer’s recommendations.

Prior to the flooring installation, the house environment must be at near occupied conditions. The subflooring should be clean dry and flat. Flat for the minimal framed system may not meet the minimum requirement. For the L/360 and a 20-foot span, the 10-foot deflection allowed can be 1/3-inch, which is more than the 1/4-inch most commonly required for flatness. Further, the subfloor may be flat enough before it is loaded with flooring, furniture, and people, but not after the loads are applied. Again where a minimum system is in place, inform the customer that the final performance may not meet their performance expectation.

 

The wood subflooring materials must not exceed 13% moisture content. Using a wood moisture meter, measure the moisture content of both the subfloor and the hardwood flooring to determine the proper moisture content. The difference between the moisture content of the wood subflooring and the hardwood flooring must not exceed 4% for strip and 3% for plank flooring.

 

The actual flooring fastener can contribute to noises if improperly placed or an incorrect fastener is used. Over driving the fastener has been shown to split the flooring tongue away from the board and compromise the fastener connection. Smooth shanked brads and other small nails don’t hold well and can contribute to noises.

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Before installing 3/4″ Solid Wood flooring, place an approved vapor retarder over the wooden subfloor. Some examples of acceptable vapor retarders over wood subfloors include: An Asphalt-saturated kraft paper such as AquaBar B or #15 felt that meets ASTM Standard D-4869 or UU-B-790, Grade D.

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Before installing 5/16″ & 7/16″ Solid

Wood flooring, place an approved vapor retarder such as a 6 mil poly over the wood subfloor.

Hardwood flooring can be affected by varying levels of humidity within homes. Maintaining the homes air relative humidity levels within the 35–55% range help protects the hardwood flooring. Advise your customers the following; 

Heating Season (Dry): A humidifier is recommended to prevent excessive shrinkage in hardwood floors due to low humidity levels. Wood stoves and electric heat tend to create very dry conditions.

 

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Non-Heating Season (Humid, Wet): Proper humidity levels can be maintained by use of an air conditioner, dehumidifier, or by turning on your heating system periodically during the summer months. Avoid excessive exposure to water during periods of inclement weather.

 

Tips on Solid Hardwood

As a general rule, a 3/4″expansion space must be left around the perimeter and at all vertical obstructions. The thickness of shoe molding is not an acceptable expansion zone.

Random-width plank is laid out with alternating courses varying by widths. Start with the widest board, then the next width, etc., and repeat the pattern.

Layout: Avoid “H” patterns. Stagger end joints of boards row to row.

 

 

Moisture Meters VS Relative Humidity Probes

 As a concrete slab dries, there is a gradual and diffuse process that must take place before it is ready for a flooring or coating application. When concrete is freshly poured, liquid water must evaporate from the surface. As that liquid evaporates, more liquid moves up through the slab to continue evaporating from the surface until only water vapor remains to move through the slab in the drying process. But by its very nature, the process means that a slab‟s surface will be “drier” than deeper into the concrete. And it is the amount of water vapor, or relative humidity that must be monitored in order to meet ASTM standards and to ensure a proper flooring application.

Keep in mind that an uncovered concrete slab will indeed have a relative humidity gradient (typically drier at the surface; much wetter at depth) throughout its thickness until a floor covering is put on top. Under normal conditions, the RH at roughly 50% slab depth will be significantly higher than the surface unless the slab has been down for a long time, and a vapor retarder is directly underneath the slab. This normal relative humidity gradient is why problems occur when relying on the use of surface tests.

 

Concrete “Moisture meters”, no matter what type, fail to provide consistently accurate „moisture‟ readings across the different mixes and densities of concrete. Additionally, other components (metal reinforcing bar, aggregate size and amount, etc.) can cause false indications of „moisture‟ especially with non-pin meters. Pin-type „moisture‟ meters are also not practical for moisture measurement because variable chemical and physical characteristics in concrete can cause false readings due to changes in electrical resistance that have nothing to do with moisture.

 

The calcium chloride test method (moisture vapor emission), and the UK-based „hood‟ method (RH) both have the same problem. They are surface tests and in reality, the surface of the concrete will more closely reflect the RH in the room or building than the conditions down inside the slab.

 

The only way you can get the true “moisture” picture, then, is by putting a probe down into the concrete and actually measuring the relative humidity within the body of the concrete. The industry standard (developed at Lund University in Sweden and adopted by the ASTM) demonstrates that a probe set at approximately 40% of the concrete‟s total depth provides the best indicator of the final equilibration once a floor covering is applied, and an accurate indicator of the conditions that will be in contact with the final flooring or coating.

 

As surface moisture tests, hand held meters (qualitative), or calcium chloride or hood method tests (quantitative) are fine, if recommended by the flooring manufacturer. But if you want the true, critical moisture picture of what‟s happening deeper in the concrete, you have to get below the surface with an in situ relative humidity probe. An accurate relative

 

Special Thanks To JJ Haines for the Article

Avoiding Slab Moisture Problems is Crucial

 In construction, if floor covering fails to remain bonded, it will quickly become the most expensive post-construction nightmare short of an earthquake. Floor covering material bond failures over concrete represent a multibillion dollar price tag to every kind of facility from homes to hospitals. Imaging having to shut down a busy facility, move patients out to another location, remove all objects in the room and then deal with the construction process needed to remedy and replace everything. The downtime costs, frustration levels and legal pursuits are historic. The only thing that is not well known about this problem is why it occurs so often.

All concrete slabs emit moisture in the form of water-vapor from the surface. If the volume of moisture exceeds the dissipation ability of the floor covering placed over it, moisture becomes entrapped between the slab and flooring. In time, the volume of moisture and the chemistry of the substance will destroy the bond of the flooring, resulting in bubbles, seam splits, curling and other physical signs that ultimately result in trip hazards, breach of sterility, and aesthetic and performance loss.

 

Most people in medical building design and construction understand the devastating effect of unwanted moisture moving in through roofing, walls, windows and HVAC systems. In fact, unwanted moisture intrusion like this represents a substantial number of construction litigation cases. Great measures are taken to minimize the potential for roof and wall system moisture, but when it comes to the concrete slab the misunderstanding is actually amazing.

 

When a slab is poured on the ground, it is usually placed over a sand layer that is on top of a plastic sheet or over a sand-bed. This plastic sheet is commonly called a vapor barrier, is better termed a retarder. (You can never stop ALL moisture vapor from entering a building, only minimize its volume to where it’s not a problem.) This measure is taken to reduce the long-term intrusion of moisture from the ground. Underslab vapor retarders however, have no effect on controlling the moisture that was inside the concrete during its construction that still has to escape.

 

The time it takes for a concrete slab to lose enough water-of-convenience to be acceptable to floor covering installations is usually considerably longer than the construction schedule. Building envelopes are supposed to be just that, but cannot become an envelope or internal environment until they are enclosed and the HVAC system is put into operation. It is then that many slabs begin to dry.

 

Those with experience in this realm already know that the floor covering material is one of the last things to be installed in a new facility and in most cases just a few days after the building has become an envelope, if even then. The acclimation of an interior creates an environmental effect on the building that draws moisture vapor out of concrete. How much moisture comes out of a given slab is governed by many variables, beginning with water/cement ratio, followed by surface profile, and ultimately drying time.

 

In most cases, buildings that are under fast track construction schedules are at risk for having all the right ingredients to create a floor bond problem. The American Concrete Institute long ago created a general rule on concrete slab drying.

When it is 70 degrees or warmer with no more than 40 percent relative humidity nor more than a 15 mph wind, concrete slabs will dry at a rate of 1 inch thickness per month. If the slab becomes rewetted anytime during the initial drying process, double that time.

 

The problem with moisture-related floor covering bond failures is discussed by every manufacturer of flooring products and is often a crowd-gathering subject when presented at seminars in the construction industry. The issue isn’t whether or not there is natural moisture to a slab that can affect the bond of the floor down the road; the issue is really whose moisture it is.

Some years ago, the floor covering community governed by the World Floor Covering Association, banded together and published an industry position paper that is easily available at their website today. This paper summarizes very well the complexities involved in achieving floor/slab compatibility but also outlines the responsibilities they feel should be taken by all construction parties.

The owner drives the construction schedule in most cases, and needs to learn that concrete will dry on its own time, governed mainly by the environment. If the slab cannot achieve a moisture condition within compliance for flooring, the owner can elect to prolong the construction schedule or pay for additional costs needed to seal the slab from the surface to render it compliant for safe installation. Those are the only choices.

However, in most cases the awareness of this potential problem is not discovered until the last hour of construction when the floor covering is ready to be installed. The floor covering contractor who is diligent and cares about their own liability, will ensure moisture tests be conducted before laying a single tile on the ground. If the tests show everything is okay, they can proceed safely. If not, it becomes an interesting problem almost immediately. In most cases, it becomes an emotional issue. The flooring contractor wants no liability for a failure and will ask the general contractor to sign off on installation. The expectation is, the sign off will protect them legally from damages if they proceed to install anyway, even over a known problem condition. If the floor contractor refuses to install until the situation is fixed, it leads to delays and sometimes incompletion damages placed on them.

The only way to address the problem is to be proactive in the specification process and to understand the time lines, the environmental conditions, and to have a plan to remediate the moisture condition prior to floor covering installation should test results come back high or unsafe. If the level is low, the allocated funds will not need to be spent. If they fail, meaning the slab needs to be sealed, then the money was already in the budget and the time was put into the schedule to fix the problem correctly. Unfortunately, in most cases the general contractor is blamed for making a bad slab when they are the first to bring up the subject of high moisture test results at the last hour. The general contractor is forced to pay more money to render it compliant for flooring, even though the fault is best contributed to the age of the concrete, not the concrete itself.

Facilities cannot afford to shut down and move out because of the floor problem, and that should be the foremost thought on the minds of everyone in the construction process. If the issue is left to blame on the general contractor or flooring sub, it doesn’t eliminate the risk or the experience of a failure, regardless of fault.

In every floor failure, the owner of the facility would confess that if they had known and understood the risk factor, they would have taken whatever precautions they could, rather than experience a costly failure and in some cases biological growth of bacteria and mold which can destroy a building. Hospital administrators are forced to lay off staff, move patients into other facilities and are at a loss to understand what happened, who is at fault and what to do next. The frustration levels are understandable, often unbearable.

So what to do? First, understand that the problem of floor moisture is one of nature, not necessarily some particular party’s fault. Second, consider the construction schedules, concrete mix designs, placement specifications, building acclimation issues and floor covering sensitivities. If there clearly is risk involved, the owner needs to have the architect specify a treatment that is proven effective to solve the problem and then pay for it. The solution has to be viable, which is another complicated subject best saved for another time.

In many cases where a plan for remediation has not been thought of and budgeted beforehand, the owner forces the architect, general and subcontractor to absorb the cost. Their attitude is that they paid to have a building made, and that’s that. But somewhere in the mix, because they are driving the construction schedule ultimately and not giving the concrete time to dry, they are forcing an unrealistic expectation. Building owners, architects and contractors need to be on the same page when it comes to this rather misunderstood but all too common problem. That starts with admitting it exists, believe it or not. Too often one hears, “We have never had a

moisture problem” only to discover that they just haven’t heard about it, for it may take a year to occur, another year to figure out what happened, and yet another year to learn enough to finally make it a legal pursuit.

The problem is far more complicated than the physics. New slabs don’t dry fast even with all the precautions taken to put vapor retarders under them. But who gets to pay for resolving the issue is an ongoing argument that occurs every day somewhere in our nation, as well as in other countries. This thing affects the homeowner to members of the Fortune 500. No one and no organization is immune. If the architect and owner agree to specify and install a remediation system then it should be done and its costs become just another part of the building. If they didn’t plan for it in budgeting but discover the potential for a problem, then again the owner should pay for a solution or perhaps give the building an unrealistic year to dry out. The moisture belongs to the owner, not the architect, general or floor subcontractor.

It’s when nothing is done that the flooring contractor is put in to a NO WIN situation and may be forced to install and risk the liability for a failure. Likewise for the general contractor, they get blamed for doing something wrong and look for the cheapest solution possible whether it’s viable or not since they have to pay for it, leaving once again the owner to suffer the consequences of downtime.

There is no excuse for a floor failure, other than ignorance. The physics are not complicated, but the social issues have always been and that is why moisture related floor covering failures continue to occur.

 

Special Thanks to JJ Haines for the Information

Hardwood Moisture Control Systems

 

Whether it’s an on-grade concrete slab or on the 15th floor of a high rise, moisture-related failures of flooring are in the millions of dollars. Thirty years ago this topic would not be as critical as it is now. Yes, we still had moisture-related failures, but there are more failures now then ever before. Back then wet curing of concrete by using water saturation, plastic sheeting, used carpet, or burlap sacks soaked with water was the common curing compound for hydration of concrete. Today, spray-on type curing compounds that can be applied the same day and left to do the same process without anyone having to come back each day for a minimum of 7 days and water the slab is the common practice. There are still projects that specify wet curing by either water soak or some sort of wet cure mat. Have cement mixes and additives changed that drastically to cause so many moisture-related failures for the flooring industry? Are cement/concrete finishers a factor? Have the adhesives we use today changed in a way that they cannot tolerate the moisture vapor emissions coming up through the slab? Let’s look at what has changed in the industry. Cement mixes have changed and will continue to change as technology keeps moving forward. Are they better? I believe they are. Cement finishing practices have improved with the use of lasers to assist in screeding the cement flat, using power trowels as finishing tools versus being done by the old knee boards and a finishing trowel.

Adhesives have improved in that they are more environmentally friendly, are very water resistant when cured and have good grab. One thing that has changed over the years with multi-purpose adhesives is that when they became environmentally friendly, solvents were removed and water was added. This means that if you have a slab that has a higher moisture moisture vapor emission rate, the adhesive doesn’t cure up like the adhesives of years ago with solvents. With moisture cured urethane adhesives that are used for glue down of wood flooring, you have just the opposite; the adhesive sets up and cures too soon, causing bonding issues as well as moisture issues.

 

So if we have all these improvements with technology, why then such high failure rates? One big factor that the flooring installer and flooring contractor has no control over is a vapor barrier beneath the slab. Without a vapor barrier properly placed underneath the slab, it’s a roll of the dice whether the flooring will succeed or fail due to moisture issues. Even with a vapor barrier placed under the slab it must be properly installed, which means that the cement finisher does not puncture the membrane. Penetrations such as pipes that come through the slab must be properly addressed, and the right membrane must be used. There are membranes that break down over time, which is why even with a membrane that was placed on the original pour, there can be failures years down the road due to moisture. The concrete industry has had controversy over the years as to whether the membrane goes directly beneath the slab, a blotter layer placed between the slab and the moisture barrier, or placement of a barrier at all. So if a barrier placed beneath the slab is going to minimize flooring failures, why doesn’t every slab have a barrier? There are reasons for that: local building codes, no specification calling for a moisture barrier, finishing issues with concrete curling; these are a few. What makes this a big headache and a costly one for the flooring industry? The installer or flooring retailers are being held accountable for moisture-related failures when they had nothing to do with the placement of the concrete. They are being forced to perform moisture testing without the required proper conditions, which in reality voids the test results.

 

Because of all these moisture issues, the flooring industry continues to evolve products available from fairly

 

inexpensive to very expensive. Do they work? Yes. Have they all had a failure? Yes. There is not a product made that is completely failsafe without the proper barrier placed beneath the concrete at time of placement. Let’s take a look at the products that are being used to minimize moisture intrusion in concrete. First you have moisture retarders; these types of products slow the movement of moisture vapor emissions coming up through the slab. These products are not moisture barriers, meaning they do not stop moisture movement; they slow the movement of moisture vapor emissions from a concrete slab. The next step up from moisture retarders is moisture barriers. These products have the ability to stop moisture vapor emissions from emitting from a concrete slab. Silicate-based moisture barrier products have been used for years with mixed success. Silicate based products are reactive type products, meaning they react with another chemical (calcium hydroxide) that is in the concrete matrix. When these products react with each other, they form a gel (calcium silicate hydrate), block the capillaries or voids in the concrete and then harden. Silicates are penetrants, meaning they go into the concrete to form a barrier; how deep depends on the density and the permeability of the concrete. This type of product is less expensive, but does not have the success rate as the products we will discuss below. Bone Dry is an example of a Silicate type product. These products are also known as concrete hardners.

 

Sealers are products that do not penetrate into the concrete but seal the surface; polyurethanes and epoxies are sealers. Epoxies are costly but have a good success rate when properly applied. There are two different types of epoxy sealers. One, the epoxy sealer is placed directly on the concrete slab with little to no prep.

Anderson Duck Shield, Armstrong VapArrest, DriTac 7000, and Sika Primer MB are examples of this type of epoxy sealer. A urethane adhesive must be applied over these types of coatings. The second type of epoxy sealer, requires a profiled (shot blasted) concrete surface. Next, the layer of epoxy coating is applied using a wet film gauge to achieve proper coverage of material. This is usually followed by a sand broadcast or the use of a primer to receive a self leveling underlayment. The sand broadcast or the primer is necessary in order for the self-leveling underlayment to bond to the epoxy coating. Mapei Planiseal EMB is an example of this type of epoxy sealer. It is good up to 25-lbs. moisture, per the Calcium Chloride test.

The hardwood industry has had a product for several years that were troweled onto a concrete slab. Once the product is troweled on, the product flows together to create a membrane. Once the product has dried, a moisture cured urethane is applied over this membrane to install the wood flooring. There are now adhesive products that can be applied during the installation of hardwood flooring that create a moisture barrier. These adhesives are trowel on and flow together much like the membranes described above. These products are known as All-In-One products. The two-in-one products are a moisture barrier and adhesive in one. A four-in-one, what they are stating is that it is a moisture barrier, adhesive, crack isolation barrier (typically up to 1/8″ horizontal plane), and sound deadening product.

Anderson enSURANCE 3X Options, DriTac 1001 and SMC, Mapei 995 and 985 are examples of these types of Adhesive products. One thing an installer/contractor needs to make certain: know your products, and work with the manufacturer of the product to assure the correct application of that product.

Hardwood Moisture Meter

 

Moisture, as we are too well aware, is a major concern to all of the floor covering trades, yet how many installers, retailers or general contractors actually conduct moisture tests on every concrete slab for direct adhered products, or what about wood sub-floors and wood installations? The floor covering industry keeps stating that it is not the responsibility of the installer to conduct the moisture test over a concrete substrate, but if one is not conducted and we install the floor covering and it fails we are responsible; sounds like a double-edged sword to me! There are products on the market that will give qualitative results on concrete and industry accepted accuracy on wood with immediate results. Moisture meters have been in the market place for years but are they properly used?

Conductance (resistance) pin type meters used primarily for wood, utilize electrodes (pins), of varying lengths from 3/8-inch to 3 inches.

 

These pins are pressed or driven into the wood and measure the resistance to the flow of direct current or low frequency alternating current, so what does this mean in terms we can understand? When the pins are driven into the wood there is a current running between the two pins, this resistance or conductance is measured and converted to a moisture content reading (MC), water is a conductor of electricity, more moisture equals higher conductance.

 

With the Conductance wood meters, there are two types of pins, insulated and non-insulated. Insulated pins have a non-conducting coating except at the tips of the pins; this is more common with the one to three inch pins. These longer pins are generally on a slide hammer or something similar, so that they can be driven into the wood material, and attached to the meter via an external connection. Un-insulated pins do not have a coating along the length of the pins therefore; the reading will register at the point where the presence of moisture is the highest between the pins.

 

Pins that are affixed to a meter are usually non-insulated and are 3/8-inch to 1/2-inch and can only read to the depth that the pins are inserted. So why the difference between insulated versus non-insulated?

 

Insulated pins, reading only at the tip of the pins, have the ability to measure gradient moisture content, as the pins are driven into the wood surface, readings can be taken at different depths to determine what the moisture content is at that particular depth.

 

An example, insulated pins can be used in situations where a reading needs to be taken on the sub-floor where hardwood flooring has been installed that may have had moisture intrusion, but other influences such as adhesive can skew the numbers.

 

When using pin type meters insert pins running parallel with the grain unless the manufacturer of the meter recommends otherwise.

 

Conductance meters read between the pins only and are sensitive to the temperature and species of the wood so make sure to refer to manufacturers manual or the manufacturer of the meter to determine the temperature and species adjustments.

 

Dielectric wood meter. This type of meter is a non-intrusive meter which means, it does not penetrate the surface of the material being tested. These types of meters are also referred to as capacitance meters. Readings are obtained by firmly placing the meter, which has a platen on the underside, in full contact with the substrate. This type of meter takes an average reading of everything within the sensing area and depth penetration. Results are displayed immediately and several readings can be taken in a very short time, as it is a non-intrusive test.

 

Depth of reading can vary with manufacturers, this particular meter that was used reads at a depth of 3/4-inch.

Dielectric meters generate an electric field much like radio waves; in fact the results are based on radio frequency (RF). Where there is a presence of moisture, the electric field weakens, how much the electric field weakens depends on a property of the material called the dielectric constant. The higher the dielectric constant (Moisture) the more the electric field weakens, and the meter will register this as a higher number. Dielectric meters must also be calibrated for different species of wood due to the specific gravity of each species. Specific gravity is a measurement to determine the wood’s density; the higher the specific gravity, the more dense the wood is. Make sure you check with the manufacturer of the meter to determine if their meters can be field calibrated for the different species. Also,

keep in mind when checking moisture for a wood installation that you need to calibrate each species for the area being tested, the floor joists, sub-floor and the product that is installed or being installed, as each will have a different setting. The numbers that you read all need to be within a combined 4 percent of each other.

For engineered wood products, contact the manufacturer to get the recommended setting, as these types of tests are more of a relative measurement rather than a semi-quantitative measurement, this is due to the glue and resins that are present in engineered products.

Concrete meters – Years ago resistance type tests were done by nailing two concrete nails into the concrete surface and then placing two wire terminals connected to a meter, many of these types of meters are still being used today but in a different form. Spring loaded moisture meters are considered Power loss meters and react to resistance of the material.

These are non-intrusive meters so placing nails in the concrete is not necessary. The meter is pressed onto the concrete until the springs are fully compressed then a reading is registered.

Dielectric meters for concrete use the relative density or specific gravity of the concrete to determine a value and use a platen (Plate) placed firmly on the concrete surface, to register a reading.

Concrete moisture meters DO NOT give a quantitative value such as the calcium chloride test. The numbers displayed on the meters are relative, meaning that it is displaying a number only, although most manufacturers recommend a not to exceed value with their meters (4.5). One can get a relative reading by taking several readings in an area to get a general idea to determine the variance in the readings. Each manufacturer uses their own set of numbers displayed on their meters, so a reading from one meter will not coincide with the numbers from another manufacturers meter. A concrete moisture meter will not give a proper reading over wood and the same applies to wood meters over concrete, each type of meter is designed for a specific use and function.

Are the meters used in situations where they are exceeding the recommended limits of their use? Yes, when inspecting an installation that has wood installed over a concrete substrate, individuals have used either a dielectric wood or dielectric concrete meter, you can use either meter but remember that you will need to find an unaffected area to get a relative value to help determine the value of the affected area. Dielectric wood meters will register a higher moisture content reading if reading through both wood and into the surface of the concrete whereas, a dielectric concrete meter will register a lower moisture content reading when reading through wood to the concrete surface. Also, keep in mind that this is a questionable qualitative test, it is just a relative reading to determine if there is more moisture in one area than another and does not give an exact moisture content due to reading the mix of materials.

Here are some tips when using meters

• Make sure you understand the specifics of each manufacturer’s meter as they have their differences.

• Readings on the wood meters generally read from 6 percent to 27 percent for the Capacitance Meters, and from 5 percent to saturation point, 30 percent on the dielectric meters.

• Make sure there is no surface moisture present prior to testing as it can skew the results.

• Pins, on pin meters MUST be in new like condition to measure accurately.

• When using conductance meters with pins that are driven into the wood material, if it is an installed product, make sure you request permission to use this type of meter as it is intrusive testing and will leave permanent holes where the pins are driven.

• Understanding the depth at which the meter reads is important as they are calibrated to a certain depth, both wood and concrete meters.

• Follow the manufactures guidelines for temperature operating range.

• Wood Meters- Check with the manufacturer to see if meters are to be used parallel with the grain of the wood or if orientation of the meter is not affected by grain direction.

• Know the size of area the meter is reading.

• Make sure you are getting full contact with the substrate being tested.

• Document, document, document; this is critical if there are any issues in the future.

Remember, if you are providing a quality product and professional installation, and fail to conduct a moisture test, it does not matter how good the product or the installation, if it fails due to moisture that was not checked and documented prior to installation either by you but preferably, an independent third party, the entire installation would be considered a failure from the beginning. Without moisture testing documentation, the liability can still fall on the installer, even though the installation procedures may not have been a contributing factor to the actual cause of the failure.

Special Thanks to JJ Haines for the Article

How to Moisture Test Concrete Floors

 

 Testing concrete slabs for excess moisture has become a common construction requirement, particularly where flooring or impermeable membranes are to be installed on top of the slab. But, while several standard moisture test methods are available, no single test reveals everything that should be considered in deciding when flooring can be installed or a coating applied. Before looking at the tests themselves, let’s review the source of the moisture. Concrete is mixed and slabs are placed with more water than will be needed for hydration of the cement. Given the right thermodynamic conditions, slabs dry over time as the excess water evaporates. How rapidly and forcefully this occurs is determined largely by the difference between the vapor pressure in the slab and the vapor pressure in the air over the slab, as well as conditions below the slab. Vapor pressure, in turn, is affected by temperature. Problems with floor coverings, such as bubbles, blisters, and delamination, occur when an impermeable floor covering or sealer traps excess moisture remaining in the slab. The key is to wait until the moisture level reaches an equilibrium point or is acceptably close to it before sealing. Pinpointing that specific equilibrium point sounds relatively simple in theory, but difficult to measure. Moisture is not evenly distributed throughout a slab, and changing environmental conditions cause moisture to move into or out of the slab. Fortunately, experience and some simple tests can help determine if the moisture content in a slab is within an acceptable range for various impermeable coverings. But first we need to know what we are measuring and what the results mean. Water leaving concrete.  Both fresh concrete and slabs that have cured and hardened have excess water. Immediately after concrete is placed and throughout the curing period, efforts are made to prevent water from evaporating from the slab so that the concrete can properly hydrate. After the initial curing period, however, we want the concrete to dry out, and large amounts of water are given off by a newly placed slab. Concrete with a higher water-to-cementitious material ratio gives off proportionately more moisture simply because there is more free moisture in the slab and the differential vapor pressure between the concrete and the air remains high. But if the concrete is simply air drying, the rate finally decreases, which means the differential vapor pressure is greatly reduced. When the water vapor approaches equilibrium, flooring can be applied. However, even after it has hardened, most concrete remains porous, so its moisture increases or decreases with changing temperature and humidity. Concrete’s permeability, the rate at which it will allow moisture to pass, depends on the size and distribution of the pores in the concrete matrix. Generally speaking, the lower the water-to-cementitious-materials ratio of a concrete mixture, the lower its permeability will be after it has cured. Concrete’s permeability can also be reduced by adding any of a number of products to fill in the voids in the concrete matrix. Moisture given off by a concrete slab in an enclosed space is a concern.

Face Dimpling of Hardwood

 The phone rings and it is an installer on the job,I am seeing raised areas where my staples shoot into the flooring where there is a lot of light coming in I inform them, that the material is not defective and inform the installer he needs to get a new nailer that costs around $550.00 to complete the job successfully or to buy a pail of urethane adhesive for over $150.00 when he bid the job figuring to use the staples he already had. This is not a pretty phone call for me. No one wins. The installer is frustrated and the home owner is very upset. These bumps or otherwise raised areas known as face dimpling, will not go away. The National Wood Flooring Association (NWFA) states that nail dimpling is a common issue when installing

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 Re-sanding and finishing the floor may remove most of the dimples but it is a tough sell to the homeowner who purchased a pre-finished hardwood. Unfortunately, replacing he floor may be necessary to resolve the situation. solid hardwood, and that using cleats can minimize these dimples. The NWFA also states that the floor mechanic (installer), type of fasteners used, and installation tools, play a large role in minimizing wood displacement. Now, not any cleat will do. If the installer chooses to use a 16 gauge cleat, he will have the same face dimpling issues. With all the new exotic flooring on the market like Brazilian Teak, Brazilian Walnut, and Strand Woven Bamboo, the typical Solid Oak Nail Gun is only going to cause you heart ache and problems. Today’s hardwood professional flooring installer needs to add a new tool to his arsenal, the 18 gauge Cleat Nailer. What happens? While traditional 16 gauge cleat-type nailers and 15-½gauge ½-inch crown staples have their place with softer hardwoods like oak, using them is usually the number 1 cause of face dimpling with these dense exotic floors. The ½-inch crown staple guns are not recommended because the drive-bar action that drives the staple is too much impact and breaks the tongues as it seats the staple. The issue is as the fastener is driven into the hardwood, the hardwood cannot absorb the thickness of the fastener. The thickness of the fastener is then forced upwards resulting in the raised or dimpled area. Always inspect for dimpling from a low angle and with back lighting because it is very difficult to see when standing directly over the area. The size of the dimpling found just above the fastener is directly related to the fastener gauge. Using a thinner fastener, such as an 18 gauge cleat helps this situation.Nail gun manufacturers have developed specialized nailing machines to accommodate thinner-gauge fasteners, thereby minimizing or reducing dimpling. JJ Haines has brought on the Powernail 50P, which is an 18 gauge nailer. This has worked well for when installing dense exotic hardwoods.