Managing moisture issues under floating floors: Flooring Forensics - May 2017

By Lew Migliore

As long as there are concrete slab subfloors, there are going to be moisture issues and challenges. It’s a fact of nature that concrete is hydrated. Water is necessary to complete the chemical process; without water, it wouldn’t be concrete. This is true whether it’s a new or existing structure, on or below grade. Moisture is to concrete as blood is to the human body.

Each concrete substrate is unique-no two are alike-and each has to be looked at in that way. Regardless of whether there were any prior issues with existing flooring or whether it’s a new construction, you can’t assume anything with a concrete floor when you’re installing over it. There is no “one size fits all” system that works. We’ll look at one concept that appears to be the perfect solution to the ever-changing conditions of the slab, but first let’s address the fact that a concrete subfloor should always be tested before applying any type of flooring over it.

Concrete testing methods have not changed significantly since 2002 when the European method of measuring the internal relative humidity (RH) within a concrete slab was introduced as ASTM Standard Test Method F2170. First, it must be determined whether or not a vapor retarder is present beneath the slab, and if it was placed correctly (i.e., directly below the concrete slab and above any earthen material). Next, is the environment at or near its operating temperature and humidity? If not, testing results will be unreliable. If the environment is stable, testing can commence.

Testing should be based on the flooring manufacturer’s specific guidelines. If the concrete slab is found to be below the specifications of the manufacturer, then measures must be taken to prep the slab to meet or exceed those guidelines. Simply because a flooring does not use a moisture mitigating adhesive and appears to be more breathable due to its flexible qualities does not mean it is a viable solution to a pre-existing moisture issue.

FLOATING FLOOR CONCERNS
What is a floating floor? Floating flooring installations are those that use no adhesive to glue them to the substrate, but instead employ some type of mechanical connection system or tabs with adhesive on them that connect the sections of the flooring together. The idea may be to minimize or ignore the importance of what may be going on with the substrate because the floor isn’t glued to it. However, you cannot ignore the moisture content of the substrate even if you aren’t planning to apply adhesive to it. Most flooring systems that are designed to float by interlocking are built with a hard backing and are non-permeable, which means that moisture vapor will not pass through the product, though it can pass between the joints.

If a non-permeable hard flooring is installed over a concrete substrate that has issues with moisture in it, the moisture, which has always been there and always moves in and out of the concrete, is going to do the same thing. When the moisture bumps its head, so to speak, on the bottom of the hard surface flooring, it condenses into water. In this scenario, the hard surface flooring is now acting as a moisture vapor retarder installed on top of the concrete substrate, and is inhibiting the escape of moisture vapor. The moisture vapor carries with it alkalinity and anything that was on the substrate, which is most often old adhesive residue and other contaminants or materials. The substrate can also harbor organic materials, such as dirt, dust, drywall paper or organic material residue in particulate form, that may have been lying there for years. You can never get all of the residual material off the substrate. So why should you be concerned about this, and what will happen?

Old residual materials will become active and move from the substrate through any opening they can find as they ride along with the moisture that is carrying them. One such example is termed adhesive ooze-old, now activated adhesive makes its way off the substrate into the openings along the edges of the flooring. With the weight of the foot traffic on the flooring, the now liquefied materials will squeeze through the perimeter areas of the flooring and ooze onto the surface at those edges. Here, it dries again, leaving a sticky residue that attracts dirt and turns dark. Once this activity begins, there’s no stopping it.

Another concern is the effect the moisture could have on hard surface flooring. Moisture can indeed affect vinyl flooring installations, causing it to react, which many times results in curling or some other form of dimensional or planar change. If wood, the product will expand or contract, since wood is still a tree in a different form-flooring-with all the same natural reactions to the gain and loss of moisture that a tree has.

MOLD AND MILDEW
Another issue of growing concern is the development of mold or mildew beneath the flooring. Mold and mildew thrive on moisture and reproduce by means of tiny, lightweight spores that travel through the air. Mold and mildew will develop within 24 to 48 hours of water exposure. All it takes for mold and mildew to grow is a moist environment, room temperature conditions and a food source. They will feed on oils on a smooth surface, such as those in some hard surface flooring materials. This also includes cold surfaces that are damp, like the lower portion of the flooring on top of the substrate, which becomes an effective microclimate that will support the growth of mold and mildew. Mold will grow in temperatures as low as 50°F and as low as 45% relative humidity. Beneath your floating floor, then, is a perfect environment for mold to grow, as all the things it needs to grow and flourish exist there. The only safe and effective way to get rid of mold is to modify the environment that contributed to its development in the first place. This means keeping room temperatures within 65° to 70°F and the relative humidity below 45%.

Despite the breathability of many types of wood flooring, the installation of floating floors over wood can also be affected if the temperature and humidity in a building or home is not controlled. Wood substrates can be a perfect source for mold growth if any level of humidity or moisture is allowed to build up on them. The bottom line is, just because you install a floating floor over a wood substrate thinking you won’t have moisture related issues, think again. By applying a floating floor over a moist wood substrate, you’ve now created a perfect environment for nature to take its course, providing mold and mildew a place to grow.

There are ways to prevent mold and mildew growth that are safe and work well. There is, for instance, a product called Floor Safe, which comes out of a technology that Dow developed several years ago. The product is also known as Bio Protect for other applications. It is so effective that the EPA has rushed it through the approval process to allow its use in sterile environments such as operating rooms. It can be applied to the substrate prior to installation to prevent mold, mildew and bacterial growth.