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by CareyBot

Q: Since you were the ones who got my daughter started on the tile-the-bathroom thing, I don’t hesitate to bring up the toilet once again.

One of the many self-help books my daughter bought before tackling this project suggested seating the toilet on plaster of Paris. This idea sounds good to me, but I thought that with all the advances in sealing products, there might be a more up-to-date solution.

Incidentally, both my daughter and I are pleased with the outcome of this project, although it was more costly than I expected, probably because of all the advice we got from Home Depot.

We have a 1 1/2-inch subfloor, which we are told needed 3/8-inch plywood over that in addition to the concrete tile backer board.

We also used premixed adhesive and premixed grout. But the bathroom looks good.

A: We’re thrilled to hear that you and your daughter tackled the bathroom remodel and did the work yourselves. We’ve often said that in addition to saving significant dollars, the real reward is the satisfaction of taking a project from “soup to nuts” and having it come out well.

Although we think you may have incurred a bit more in costs and heft than you need, you still saved a ton of money and didn’t have to deal with the problems contractors sometimes bring. Congratulations.

You mention a 1 1/2-inch subfloor. This tells us that the subfloor is probably tongue-and-groove pine or fir installed over 4-inch beams. The key to a successful floor tile job is to make sure the substrate doesn’t flex too much. If it does, the grout lines and even the tile can crack.

Three-eighths-inch plywood sandwiched between the subfloor and tile backer board seems to be overkill to us. We’d approach it a different way if we had any doubt about the bathroom floor’s ability to carry the load. We would have installed another 4-inch beam on concrete piers and posts in the crawl space between the existing beams. This reduces the span by half and increases the load-bearing capacity of the subfloor exponentially. In your case it would also have lowered the bathroom floor by 5/8 inch.

It’s interesting that you mention plaster of Paris as a method to ensure a stable commode. Another reader, Tom Pallante of Sausalito, Calif., told us that his grandfather, a master plumber in New Jersey, used this method as his standard to secure commodes he installed. He relates the method his grandfather used in this note:

“Level the toilet with shims. Leave the shims long enough to allow for adjustments. Mark the placement of the shims on the toilet, the floor and the shims (this allows for realignment of the shims if necessary).

“Put plaster of Paris along the bottom edge/rim of the toilet before it is set in place. Align and set the toilet on the marked shims. Once the plaster sets slightly, remove the shims and fill the spaces with more plaster.

“The plaster will not shrink, but to keep it from setting too quickly, add a little white vinegar to the water when mixing the plaster.

“Plaster, similar to unreinforced concrete, is good in compression, but not in tension, so the toilet will stay solidly in place and not leak, but can be removed easily. Clean off the excess plaster, let it dry completely and caulk around the toilet.”

It seems to us that this is a good method for securing a toilet on any type of floor regardless of the condition. However, as you presumably have a flat new floor, using plaster of Paris probably is an unnecessary step.

Shimming should be minimal, and a high-quality caulk around the base of the toilet leaving a 4-inch gap in the back should do the job.

That said, using plaster of Paris to ensure a rock-free commode is a surefire “belt and suspenders” approach used by a master craftsman. You could do worse than follow this advice.