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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 (Photo 1).

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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 (Photo 2)? 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 board and finishing trowel.

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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 envronmentally friendly, solvents were removed and water was added. Which 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 a moisture cured urethane that’s 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.

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So if we have have all these improvements with technology, why then such high failure rates? Because of one big factor that the flooring installer/contractor has no control over, a vapor barrier beneath the slab. Without a moisture/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 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? Good question; there are reasons for that: local building codes, no specification calling for a 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 retailer are being held accountable for moisture-related failures when they had nothing to do with the placement of the concrete. The statement that the installer/contractor, is not responsible to take the moisture readings is true, but we need to finish the sentence. It is the responsibility of the installer/contractor to make sure that moisture testing has been conducted prior to starting the installation. It’s that last part of the statement that seems to place so much blame on the installer/contractor.

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So, what has the flooring industry done about moisture issues? There are numerous 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 type 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 capilaries 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 viscosity and the permeability of the concrete. 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. Here is a product that is a three-step application. Photo 3 shows the first layer of epoxy being applied. Photo 4 shows the second layer of epoxy being applied; the different color helps the installer make sure that he or she is getting proper coverage of material. This is followed by a sand broadcast (Photo 5) to receive a self leveling underlayment. The sand is necessary in order for the self-leveling underlayment to bond to the epoxy.

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The hardwood industry has had a product for several years that is troweled onto a concrete slab. Once the product is troweled on, the product heals, or flows together to create a membrane (Photo 6). Once the product has dried, a moisture cured urethane is used to install the wood flooring. There are now products that can be applied during the installation of hardwood flooring that create a moisture barrier. These products are known as two-in-one, and four-in-one products. The two-in-one products are a moisture barrier and adhesive in one. When manufacturers state that their adhesive is 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 (Photo 7). One thing an installer/contractor needs to make certain: know your product, and work with the manufacturer of the product to assure the correct application of that product.  We don’t have the time or space to write all the concerns with moisture and concrete in this article, but installers/contractors need to be proactive with the education of this subject whether we like it or not. If you want to protect your business and your installation, it is in your best interest.