Flooring Contractor Spring 2015 : Page 18

I N S T AL L A T IO N FE A T U R E Moisture Misconceptions Don’t Make Assumptions When it Comes to Concrete BY CHRISTOPHER CAPOBIANCO, ECORE COMMERCIAL FLOORING F ar too many construction profes-sionals cling to misconceptions and make assumptions regard-ing concrete and moisture-relat-ed problems. They either don’t know or they are ignoring these issues to save time and money. Even worse, they often use these assumptions to tell flooring contrac-tors that moisture testing and mitigation are unnecessary or accuse floor covering and adhesive manufacturers of trying to “cover their assets” by blaming everything on moisture. Here are some examples of those assumptions, and some language and industry standards that can be used to strengthen your case for doing things the right way. I often quote ASTM F710 Standard Practice for Preparing Concrete Floors To Receive Resilient Flooring. Every flooring contractor should have a copy. It applies to all types of flooring, as noted in the scope; “ Although carpet tiles, carpet, wood flooring, coatings films and paints are not specifically intended to be included in the category of re-silient floor coverings, the procedures included in this practice may be useful for preparing concrete floors to receive such finishes.” Concrete cures in 28 days, so let’s install the floor then. According to ASTM F710, “New concrete slabs shall be properly cured and dried or treated before installation of resilient flooring. Drying time before slabs are ready for mois-ture testing will vary depending on atmospher-ic conditions and mix design.” Notice that “cured” and “dried” are used in the same sentence. They are not the same thing! Curing is the chemical reaction when the cement powder, water, sand and stone bond together to make concrete. This process needs water, so Proper concrete moisture testing is required by industry standards and manufacturers of floor coverings, adhesives and patching/leveling compounds. curing is designed to keep the water in initially. After the concrete cures, drying starts as the excess water evaporates. “28 day cure” refers to the approximate full cure time for standard mix four-inch thick concrete. But, after 28 days, the concrete is not dry. A common rule of thumb is that drying takes about 1 month per inch, so it could be months before a standard mix concrete slab is dry enough to cover with a floor covering. I used the term “standard mix” to call your attention to the difference between Standard and Lightweight concrete, which segues into another common false assumption. You don’t have to worry about mois-ture problems in slabs above grade. Standard mix comes directly out of the truck, is placed on or below grade or hoist-ed to upper floors using a crane. Tradition-al formed concrete above grade dries from both sides, but if its on a metal deck that’s not the case. Plus, a lot of concrete today is pumped through hoses to get it upstairs. A lot of these mixes use lightweight ag-gregate, which has advantages on the construction side, but takes a lot longer to dry. ASTM F710 calls this out and this is a good warning for construction and floor covering professionals: “ Floors containing lightweight aggregate or excess water, and those which are allowed to dry from only one side, such as concrete over a moisture vapor retarder or concrete on metal deck construc-tion, may need a much longer drying time and should not be covered with resilient flooring unless the moisture vapor emission rate or percentage of internal relative humidity meets the manufacturer’s installation specifications. ” In one side-by-side study, a standard mix six-inch slab took 46 days to dry while the lightweight concrete took 168 days. Curing compounds are necessary. Initially, the water in concrete needs to 18 The Flooring Contractor Magazine Spring 2015

Moisture Misconceptions

Christopher Capobianco

Don’t Make Assumptions When it Comes to Concrete

Far too many construction professionals cling to misconceptions and make assumptions regarding concrete and moisture-related problems. They either don’t know or they are ignoring these issues to save time and money. Even worse, they often use these assumptions to tell flooring contractors that moisture testing and mitigation are unnecessary or accuse floor covering and adhesive manufacturers of trying to “cover their assets” by blaming everything on moisture. Here are some examples of those assumptions, and some language and industry standards that can be used to strengthen your case for doing things the right way.

I often quote ASTM F710 Standard Practice for Preparing Concrete Floors To Receive Resilient Flooring. Every flooring contractor should have a copy. It applies to all types of flooring, as noted in the scope; “Although carpet tiles, carpet, wood flooring, coatings films and paints are not specifically intended to be included in the category of resilient floor coverings, the procedures included in this practice may be useful for preparing concrete floors to receive such finishes.”

Concrete cures in 28 days, so let’s install the floor then.

According to ASTM F710, “New concrete slabs shall be properly cured and dried or treated before installation of resilient flooring. Drying time before slabs are ready for moisture testing will vary depending on atmospheric conditions and mix design.”

Notice that “cured” and “dried” are used in the same sentence. They are not the same thing! Curing is the chemical reaction when the cement powder, water, sand and stone bond together to make concrete. This process needs water, so Curing is designed to keep the water in initially. After the concrete cures, drying starts as the excess water evaporates. “28 day cure” refers to the approximate full cure time for standard mix four-inch thick concrete. But, after 28 days, the concrete is not dry. A common rule of thumb is that drying takes about 1 month per inch, so it could be months before a standard mix concrete slab is dry enough to cover with a floor covering.

I used the term “standard mix” to call your attention to the difference between Standard and Lightweight concrete, which segues into another common false assumption.

You don’t have to worry about moisture problems in slabs above grade.

Standard mix comes directly out of the truck, is placed on or below grade or hoisted to upper floors using a crane. Traditional formed concrete above grade dries from both sides, but if its on a metal deck that’s Not the case. Plus, a lot of concrete today is pumped through hoses to get it upstairs. A lot of these mixes use lightweight aggregate, which has advantages on the construction side, but takes a lot longer to dry. ASTM F710 calls this out and this is a good warning for construction and floor covering professionals: “Floors containing lightweight aggregate or excess water, and those which are allowed to dry from only one side, such as concrete over a moisture vapor retarder or concrete on metal deck construction, may need a much longer drying time and should not be covered with resilient flooring unless the moisture vapor emission rate or percentage of internal relative humidity meets the manufacturer’s installation specifications.” In one side-by-side study, a standard mix six-inch slab took 46 days to dry while the lightweight concrete took 168 days.

Curing compounds are necessary.

Initially, the water in concrete needs to Be kept within the slab for several days so that the chemical reaction (curing) can occur. Traditional concrete curing employed wet burlap on top of the new concrete surface, and you’ll still see that on highway projects sometimes. For floor slabs, this method has been replaced by “membrane forming” curing compounds, which seal the surface and allow construction to begin on top of the new slab a day or two after it is placed. Problem is, curing compounds are still on the surface long after the initial cure, so the moisture doesn’t evaporate out as quickly, and these compounds may not be compatible with floor covering adhesives. ASTM F710 and guidelines from floor covering and adhesive manufacturers call for slabs to be free of curing compounds, so they should be removed sooner rather than later to help the concrete dry faster. Even so-called “dissipating” compounds don’t dissipate evenly; so don’t let someone convince you that these are an option. A better option is the “cover cure” method that uses waterproof paper or plastic sheeting for several days to hold in the water needed for the initial cure. Once the “cover” is removed, the drying process can start. This faster variation on the burlap method is beginning to gain acceptance, so if you have any input, ask the architect or the general contractor to consider this method.

You don’t have to worry about a moisture problem in the desert.

Tell that to the thousands of building owners in the Southwest who have had moisture-related failures. In reality, they have as many or more problems than the rest of the nation. One possible cause in warm climates or summer installations in the north is that extra water is sometimes added to the truck keep the mix “alive” in the heat. This adds to the drying time. More seriously for slabs in the desert is the practice of not installing a vapor retarder sheet beneath the slab, assuming that the ground is “dry. “ There is always moisture in the ground that moves upward, and often the water table in a desert environment is high. Again, according to ASTM F710, “Every concrete floor slab on- or belowgrade to receive resilient flooring should have A moisture retarder (often improperly called a vapor barrier) installed below the slab.” The American Concrete institute also specifies this in their document 302.1R, Guide for Concrete Floor and Slab Construction.

Don’t worry — it’s a 30-year old building!

“Adaptive re-use” is a leading cause of moisture failures. Warehouses are changed to shops or offices, garages are changed to living space, basements are converted, etc. One of the worst moisture problems I’ve ever seen was in a 30-year-old warehouse building that was converted to a furniture store.

Because the slab was not designed to be covered, there was no vapor retarder in place beneath the concrete. For 30 years, ground water vapor moved through that slab unnoticed, until the floor was covered with sheet vinyl and the adhesive turned to mush.

There was no moisture problem with the old floor!

Although some experts don’t agree, many feel that the old flooring types “breathed “ More than the current generation of products. And some feel that the old solventbased adhesives better resisted moisture. The jury is still out on these points but the fact is that flooring and adhesives are not the same today as they were 25 years ago. So, moisture may have been moving unnoticed through the older floor covering types, or the water table may have risen over the years. Cover that floor with resilient tile or sheet, or vinyl-backed carpet, and the vapor has nowhere to go but into the adhesive.

It didn’t look wet. It didn’t smell wet. It didn’t feel wet. We’ve never had a moisture problem, so we don’t test.

If you are going ahead with a floor covering installation based on any of these assumptions, you are asking for trouble! The first defense is detection. You need to understand what you’re facing every time you start a flooring installation over concrete.

Every flooring, adhesive and patching compound manufacturer has a written variation on the industry standard, ASTM F710, that says “ALL concrete slabs shall be tested moisture regardless of age or grade level.” Whether it’s concrete in the basement or on the 50th floor, and whether it’s brand new or 50 years old. Looking at it, smelling it or touching it tells you nothing about the Invisible water vapor that may be migrating out of that concrete slab. If you have never tested and never experienced a moisturerelated failure, then you’ve been very lucky!

I tested with a moisture meter.

I tested with a sheet of plastic.

Meters yield a momentary snapshot of the moisture situation but the rate of concrete vapor emissions can fluctuate from day to day. The plastic sheet test has proven unreliable and is being removed from a number of industry standards. There are only two ASTM test methods for concrete floors; F1869 (Calcium Chloride test) and F2170 (Relative Humidity test). The manufacturer will tell you which method is preferred.

In the final analysis, sufficient information is available on moisture-related failures as well as how, when and why to test. There really is no excuse for not testing. And that’s the best way to get around all of these misconceptions and assumptions.

Resources

ASTM International: www.astm.org.
American Concrete Institute: www.Concrete.org

Christopher Capobianco has been in the floor covering industry since the 1970s and is currently with Ecore Commercial Flooring, focusing his efforts on sales in the New York City area. He served as FCICA Chairman from 2005-2011 and still serves on the Executive Board and several committees. He has been a regular contributor to The Flooring Contractor and many other trade magazines dating back to the 1980s. A member of ASTM Committee F.06 on Resilient Flooring since 1993, he was a long time chair of the task groups that developed ASTM F710, and ASTM F3008 Specification for Cork Floor Tile. You can reach him at EcoreNY@gmail.com.

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