Concrete flooring: Mitigating vapour-related failures

Photos courtesy Maxxon

By Heather (Yario) Rice

Whether for new construction or renovation, proper subfloor preparation is essential for executing a high-quality floor installation while extending the life of the finish flooring. In the last 20 to 30 years, regulations on volatile organic compounds (VOCs) have made buildings safer for occupants; however, these regulations have also created new challenges for designers and general contractors, as in the case of moisture vapour-related flooring failures.

As the industry’s understanding of moisture emissions has grown, so have the types of solutions to mitigate the problem. Today, a new category of moisture barriers makes it easier and more cost-effective than ever to properly prepare concrete for finish flooring.

On July 2, 2003, ozone and its precursors, including VOCs, were added to Schedule 1 of the Canadian Environmental Protection Act, 1999 (CEPA 1999). This provided Environment Canada with additional tools and the legal authority to develop and propose measures to control VOC emissions. Since then, Environment Canada has continued to review and update its regulations on VOCs. On May 2, 2015, a proposed order to amend the definition of VOCs as listed in Schedule 1 of CEPA 1999 was published in the Canada Gazette, Part I. Removing solvents from adhesives made them VOC compliant; however, the resulting products were sensitive to moisture vapour in a way the industry has not seen before.

An anhydrous calcium chloride (CaCl) test for ASTM F1869, to measure the moisture vapour emission rate (MVER) of the concrete subfloor.

In the author’s observations, prior to the adoption of VOC regulations, moisture-related failures were largely unheard of. They noticed flooring failures began to occur with frequency in the early 2000s. The flooring industry quickly learned moisture vapour emissions were to blame. Not only were these types of emissions common, but they could also result from a wide variety of sources. Slabs, especially on grade, can vary in moisture content and emission levels. From groundwater intrusion to major weather events, the amount of moisture present could vary throughout a slab, increasing and decreasing seasonally and throughout the life of the building. Slabs that tested with low moisture emissions could still have a failure weeks, months, or years down the road.

Common construction practices also held the potential to cause moisture-related issues. The process of burning or hard trowelling a slab was used to achieve floor flatness but had the secondary effect of sealing the surface. Applying a cure-and-seal expedited the curing process and sealed the surface to protect it from trade damage. When it came time to install flooring, manufacturers would require the surface of the slab to be opened to remove bond breakers.

Since both processes trapped moisture in the slab, opening the surface allowed water vapour to exit as the relative humidity (RH) of the slab sought equilibrium with the ambient conditions on the jobsite. Not only did this cause condensation to form at the bond of the adhesive to the slab, but it also could pull alkalinity from within the slab to the surface, creating a high pH environment. Standard adhesives could handle a pH of up to nine, while a freshly opened slab could easily reach a pH of 11 in a short timeframe.

Below the flooring, one of two things would happen: either the adhesive would not dry or adhesive that was dry when the flooring was installed would emulsify. This is where mould, mildew, and other aggravating floor failures would start. As with any emerging issue, preliminary testing and solutions needed to be developed before improvement was possible.

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