I met a General Contractor at one of my clients home today and he said they often do not tear up the tile in the master shower when there is a mud pan below. They will put levers over and tile over it all. SERIOUSLY? Anyone do this with luck?
Sounds wickedly risky in my book!
I found that how to from Find Homebuilding to be ok as long as the shower is on a cement floor. What is not addressed in that forum is the moisture that gets past the tile and grout. All shower drain assemblies have a secondary drain point that is below the surface of the tile. Its primary being is to allow moisture that collects below the tile in the mud bed to have a way out of the system without collecting and causing damage to the floor above. The writer goes on to say that he uses a generous amount of thinset to place the new drain grate into place. I would be weary of this as it is possible for that material to plug the drain system located below the surface of the tile. In addition the writer uses a water membrane system. This is a great idea, however proper protocol dictates that this membrane not cover or seal off the below floor drain openings that are critical in preventing leakage should the water membrane fail. This point is all mute however if the shower pan is placed on a cement slab at or below grade level as any leaks will seep into the ground and evaporate away. The old adage goes your only as good as the weakest link. And if any tile on the floor or if the original installation is faulty then your new expensive floor would end up needing to be torn out to make the repairs that eventually will arise in short order.
Here is his reply after I noted my grave concerns.. "Ok I admit it was probably a bad suggestion in this case, and I didn't mean to imply we would do it that way. Only that it might be a possible way to save some work if the right conditions existed. I understand not every tile guy is comfortable with the technique but most tile manufacturers do give detailed instructions on how to do it and offer products specifically designed for tiling over tile. Likewise we would never do anything we couldn't stand behind, I would have discussed it in more detail with my tile person before proposing it in an estimate. That being said we won't mention it again. "
In the midst of a bathroom renovation at our church the member overseeing the project (a construction o. supervisor) urged us to just level and then tile over the old 1960 tile job. To save money we agreed but the subcontractor HE contracted wouldn't do it, seeing it as a bandaid over bad. Luckily we listened to him as the flooring supports were rotting and would have failed. Think of how long a tiled shower will be in place. Now divide that by the extra cost of doing it right. It will probably work out to pennies a day.