Spencer Nath


When we look at problems associated with wood flooring and moisture, we naturally expect to see expansion; this can manifest itself in the flooring buckling or we could see warpage, either cupping or crowning depending on were the moisture is coming from.


Notice the discoloration due to mold growth in the flooring.

But there is another problem that you may not be prepared for, mold. Wood flooring, especially laminate products, already have everything mold spores need to begin multiplying, except moisture; it’s the key element in microbial growth. Mold spores are everywhere in our environment so the seeds for growth are there. Wood and especially the adhesive in laminate products provide the food or growing medium, so all we need now is the activator for growth, moisture. And it doesn’t take that much moisture to begin this growth. It’s a misconception to think that mold will not grow if the moisture content is below 20 percent.  Aspergillus and Peniceillium can become active colonizers at 16 percent wood moisture content, an easily achievable figure were vapor emission rates exceed manufacturer limits on concrete slabs.

Moisture can cause problems related to mold growth without the visible evidence that we normally associate when we suspect there is a moisture problem, such as with the above-mentioned warpage or buckling.

The discoloration in the flooring can be seen here.

Notice the discoloration in Photos 1 and 2. It’s baffling until you look at a dissected piece of the flooring, shown in Photos 3 and 4; you can see that microbial growth has begun inside the wood flooring between the laminate layers. Moisture, as it moved through the porous layers of the laminate wood floor ing elevated the moisture content of the wood to the point that it would support microbial growth. If you examine Photos 1 and 2 again, you will see tiny black dots, again microbial growth just under the urethane layer of the flooring. The moisture eventually hit the cap, the non-porous urethane wear layer, and as nature wants to do the wood began to equalize in moisture content, with this moisture source the already present mold spores began to grow. This growth in turn began to discolor the flooring. It was at that point the new buyers of this very expensive home contacted their lawyer and he contacted me.

Wood is naturally porous but when we put a cap on that porous natural product with a urethane wear layer we trap moisture at that wood/urethane interface and moisture accumulates providing the moisture source to activate microbial growth.

Notice the mold on the back of the flooring.

Vapor emission rates on this below grade concrete floor were 7.4 pounds, the manufactures recommendations were for no more than a VER of 3 pounds, and of course proper testing was not done prior to installation.

The cost of this simple problem with approximately 400 square feet of flooring was $20,000; that’s $50 a square foot, pretty expensive laminate wood.

This case was settled in mediation without the flooring company being involved. Had the buyer and seller not been agreeable to settle this you can bet the flooring company would have been writing the check for this problem because they didn’t see the need to conduct a few $10 calcium chloride tests before proceeding with the installation.

A hot air gun with welding tip

Now you might reason that since this house was built in the 1940s the concrete should be sufficiently dry, but given that if a vapor retarder was placed under the basement slab, which is unlikely, it was more than likely not installed correctly and a problem still very prevalent in today’s construction community. And if it was placed correctly it had probably deteriorated to the point of no longer being effective. The concrete slab if in contact with the ground will equalize its moisture content to match that of the ground usually 90%-100% relative humidity. No amount of time will dry a slab in contact with the ground.

The installer tried to prevent moisture from impacting the flooring with polyethylene sheeting but it proved ineffective.

This all goes back to what can happen when we don’t pay attention to the details. Proper testing would have revealed the moisture problem and it could have been addressed, as it is now it has become a costly problem that may still have residual health and monetary consequences.