Vinyl Floor Installation and Repair Q&A

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Dear NH,

I want to put vinyl flooring over the concrete floor in my basement bathroom. Can I or should I seal the concrete in some way first to avoid any moisture problems due to moisture seeping up through the floor?

DW from Winnipeg, Manitoba, Canada


Installing vinyl flooring over concrete can be risky business. I have done quite a bit of condominium work and have seen many vinyl flooring failures… adhesive failure, discoloration and curling… on these often slab-floored dwellings. The primary risk factor is the amount of moisture in the concrete floor, or "slab". High levels of moisture can cause the flooring adhesive to release from the slab, or maybe never dry completely at all! This can cause discoloration in the vinyl over time that is not usually covered by the manufacturer's warranty. Each flooring has an "acceptable" level of moisture so getting this information from the manufacturer is essential.

And that's not all! There is a second factor that cannot be overlooked, and that is the alkalinity (pH) of the concrete. Highly alkaline materials can burn skin and deteriorate metals. Fresh concrete is very alkaline; hence, the safety warnings on cement bags concerning skin and eye contact. However, as the concrete ages, the alkalinity on the surface usually decreases. In some cases, though, the concrete retains its alkalinity! When vinyl flooring is installed over it, the moisture that becomes trapped at the adhesive/concrete bond becomes increasingly alkaline as alkaline minerals migrate to the moisture. The result can be deterioration and eventual failure of the adhesive as well as staining in the floor. This can occur even when the concrete moisture level is acceptable!

To prevent the later pain and suffering of flooring failure, the two things you should do are 1) get a calcium chloride test kit to determine the amount of moisture moving through the slab and 2) get an alkaline test kit. Either of these products can be purchased at a flooring supply or home store.

The calcium chloride test involves placing a pre-measured canister of calcium chloride, an absorbent salt, on the concrete floor and covering it with a small plastic dome supplied with the kit. Calcium chloride absorbs moisture from the air at a known, fixed rate. By comparing the initial weight of the canister to the weight after a specific amount of time… usually 24 hours… you can find out how much water the calcium chloride has absorbed. Using a mathematical formula, you can arrive at the number of "pounds of water per hour" that are rising through the slab. Each vinyl flooring manufacturer has a maximum acceptable level for this figure. (If the name "calcium chloride" sounds familiar and you live in snow country, you have probably used it... the environmentally friendly chemical used for melting ice and snow!)

The concrete alkaline test kit is similar to its a swimming pool test kit. The concrete surface should be clean and stripped of any coatings. If necessary, you can use adhesive removers or a rotary floor sander to clean the surface. Concrete tends to be alkaline, but the surface has the lowest alkalinity due to aging. Therefore the concrete surface should not be ground down more than a very small amount.

A small quantity of pH-balanced distilled water (supplied with the kit) is applied to the floor. After a predetermined amount of time a pH test strip (again, similar to a pool pH test strip) is moistened with the water on the floor. The color of the strip determines the pH, which is compared to the vinyl floor manufacturer's specifications. There is a second type of kit that uses a

If you have high levels of either moisture or pH, there are some actions you can take. There are some concrete sealers that can be used which may lessen the moisture AND pH to acceptable levels… but there are no guarantees! Be careful… choosing the wrong sealer can make a bad situation worse! So be sure to purchase a sealer that is compatible with the flooring adhesive.

You can, of course, lower the pH the old fashioned, dangerous and sloppy way. First, wash the floor with a 10% solution of muriatic acid, applied with a stiff brush with a handle. Rinse the floor clean water and then apply a neutralizing solution of 1 cup household ammonia to 1 gallon water followed by another rinse. After thorough drying retest the floor for pH.

You can read more about the USES AND DANGERS OF MURIATIC ACID at the website…

Dear NH,

I had a rug stain my white vinyl floor a yellowish color. It was near a patio door. I removed the rug and a few weeks later the stain had disappeared. I believe the direct sunlight shining on the floor caused the stain to disappear.

Maybe you want to amend your article using this information.

JW from Milwaukee, WI


Interesting... and I guess it makes sense, too! Sunlight is known for its power to fade colors. Just ask anyone who had a couch that is now "two-toned" because of strong sunlight! You are fortunate to have your floor stain so conveniently close to a window.

Maybe this could be used as a marketing tool for skylights?

More info on vinyl floor stains at: