Tech Tip – Q&A with Mark Heinlein

Question: My company is about to supply and install about 2,000 square feet of porcelain wood look tile in a home where the previous flooring failed due to water intrusion into the home.  I am not confident that the water issue was remediated correctly. The concrete looks dry, but I am concerned about any future issues with moisture in this slab.  We’ve never tested for moisture when installing ceramic or porcelain before, and I’m not sure what I am to do if the concrete tests high.  Could you please guide me in this situation?

ANSWER: Thank you for contacting the National Tile Contractors Association.

Before proceeding, you need to do some research as to what caused the original failure.

What was the water intrusion?  Was it surface water, moisture vapor transmission (MVT) or hydrostatic pressure?  All three are distinctly different in cause and effect.

If it was surface water (topical flooding of some sort) the old floor (if properly installed) should have survived, been cleaned up and remain today.  If it was not properly installed, the failure could have been exacerbated by any or all of these – poor bond coat coverage, incorrect mortar selection, a surface contaminate or bond breaker on the concrete, a dry slab or high temps causing the mortar to skin over at time of installation, incorrect application of a membrane, etc.

In most cases moisture vapor transmission won’t affect a tile on concrete installation.  Normally, the vapor will find its way to the chimney (grout joint) and find equilibrium.

If the failure was caused by hydrostatic pressure, the source must be fully remediated before continuing.

If the slab is saturated due to a high water table or poor water management with gutters and downspouts, the mortar will not bond at all.  This is similar to placing a wet porcelain tile into fresh mortar – there will be no transfer to the back of the tile since the water acted as a bond breaker.

It is possible to test the concrete for the presence of water using calcium chloride or relative humidity tests but if the water increases different times such as spring runoff or heavy rains the testing may be inconsistent.

If crack isolation membrane is required on the slab, be advised that some membranes are not able to remain bonded to a substrate affected by water pressure.  There are however some membranes their manufacturers state are able to withstand water pressure from beneath the substrate.  Depending on the situation an uncoupling membrane may be one solution.  An unbounded mortar bed installed on a drainage mat may be another.

Mark Heinlein
NTCA Training Director