Every time an installer looks at a new job, the condition of the substrate needs to be reviewed thoroughly to determine if the surface to be tiled is adequate. If the surface is contaminated in any way, the architect, general contractor and/or the owner must be notified by letter or email.
All too often, the jobsite visit will reveal that the concrete floor has an off-white or light beige-colored primer residue on almost the entire floor from the careless painter coating the ceiling. The spray-applied primer is “designed” to be completely dry before it falls to the floor, which allows it to be swept away easily. However, any installer who has been on a construction site knows this is usually not the case. Instead, that paint is now well-bonded to the concrete and is not able to be removed with a six-inch flat blade or a razor scraper.
The reason I labeled the painter as careless is due to the fact that this mess should never have occurred in the first place. The painter should have placed a drop cloth on the floor, pausing briefly to move it as needed. Unfortunately, this seldom happens.
The tile installer now has to make a decision: accept the floor as-is and tile over it (remember: once you tile it, you own it) or write emails to all the interested parties which may delay the schedule and create an unhappy general contractor. We all know the paint should be removed, without question. Push comes to shove, and the tile installer is going to start right away. His or her only way to get a good bond to the painted surface is to buy the mortar manufacturer’s “super sticky stuff” and get it done. The job is complete. Everyone is paid and life is good…until the owner calls saying, “We have hollow-sounding tile which is not acceptable.” A quick trip to the jobsite reveals just that. Now it’s time to call the mortar manufacturer, since the thinset didn’t bond to the floor.
When the mortar rep arrives, a tile is removed (as seen in the attached photo) showing the tile with thinset mortar well-bonded to the back. The interesting thing here is that some of the paint is well-bonded to the thinset and some of the residue is still on the concrete. Now comes the reality check: the installer is at fault. (Remember, the paint should have been removed.)
The thinset manufacturer is in the clear. The product used did what it was designed to do: bond the tile to the surface beneath. Unfortunately, in this case it was to the paint, not the concrete. The last time I checked, paint manufacturers don’t warrant their products as a bonding agent for thinset mortar.
Stick to your guns and get paid (as you should) to fix or clean the floor before the job begins. Otherwise, the cost of the callback and replacement tile work comes out of the installer’s pocket. A lose-lose situation, no matter how you spread it.