I have a question that the internet can’t seem to answer for me. I am building a platform for a drop in tub. My plan was to frame it in 2x4s, then top with 3/4" outdoor rated plywood, then 1/2" backer board, then finally tile (leaving height for tile and 1/8" for mortar). The lip would rest on the top of the tile.
Then, the daughter told me what “tile” she wanted, and it is basically river rock. Knobbly and pebbly. I don’t think I want to rest the lip of the tub on that, so what do I do? Just rest it directly on the backer board and caulk between the backer board and tub, then run the stone just up to it? Can I rest the tub directly on the backer board? Can I get a good seal somehow?
You can do that. You can also level the top of the stones with mortar where the tub would rest on it.
Either way offer an advantage, or is it 6 of one half a dozen of the other?
I think you’ll have a bit of advantage setting the tub on the tile … as this allows for a positive drainage … setting the tub on the backer and then tiling to the tub leaves a small crack for the water to accumulate … use a very good quality chalking (make sure it says explicitly “100% Silicon”) and neither should be a problem …
Maybe this is overkill, but check the prices on marine rated plywood … just to make absolutely sure …
As a design concept, consider using a regular tile as a frame for the pebbles (that’s what they are usually called, I think). Then set the tub on the “frame”. You can make it with almost no reveal from the tub, or give yourself 1/2" or 1" so it doesn’t look like a mistake.
A/The current rage in swimming pool “plaster” is a product with colorful pebbles embedded.
I do not know if this is available in small quantities or for DIY.
If you can find it, you will have both the river pebble look and a waterproof material flush enough to rest the lip on it.
You may well find a pool builder who is hungry enough at this time of year to take on the job.
Can’t hurt to ask…
Why would she want something “knobbly & pebbly” around a hat tub? Sounds quite uncomfortable to walk on; even more so to sit or lie on.
It’s trendy for bathrooms now, especially sower floors. Once it’s grouted, it doesn’t feel particularly bumpy.
I assume the OP is talking about this stuff.
With bath tubs it is standard procedure to install the tub first and tile up to it. Tile is grouted and a bead of silicone is applied between tub and tile which helps to reduce creaking as the tub will move more than the tile. The main reason for this is ease of plumbing, but it is also going to be less prone to creaking than installing the tub on top of tile. We usually leave an access panel for plumbing behind a section of tile that can easily be replaced for plumbing repairs.
The backer board is not really necessary, thinset likes plywood: OSB or dimensional lumber is a no go. For the many tub skirts and drop in tub decks I have built we have never used tile backer overtop, and I have worked with some pretty fussy high end tile setters. Bumping the plywood up to 1 inch is not a bad idea.
Protip: seat the tub in a bed of mortar sand mix to give it a really solid bottom. Many plumbers will partially fill the tub with water then spray foam under it for the same purpose.
As far as what tile I was talking about, this is the exact one we were looking at. There would be a thin 3" border around three sides of the tub, and a slightly less than 2’ long deck (shelf, ledge?) at one end.
A general contractor buddy came over and told me basically what FluffyBob said in his first paragraph. I believe he worded it as “You don’t want to build this beautiful tile deck then make it look like you dropped a cheap fiberglass tub in, do you?” He suggested resting the tub lip on the plywood directly (or even the framing), then bringing my tile up to meet just below the top of the lip rather than go under it.
Thank you to everyone who answered. I’m more of a math and science guy, so I was thinking there was one right answer, rather than it being an art form.
One more (set of) questions. I have a plumber who might be installing the bath. He said he would do a mud set, as FluffyBob suggested, and as I wanted. The tub I bought (used) is made of acrylic over fiberglass. On the bottom, there is what looks like 3/4 OSB, then two 2x4 runners under that. All of it is fiber-glassed in, by which I mean it does not look like packing material at all. Can you still do a mud set under that? Will it just take a buttload of mud? How much room should I leave for the mud set when planning my framing height? (I’ll ask my plumber, but I like to have multiple sources so I can give him ideas if needed…)
I have seen a few tubs with glassed in feet that the installer said you were not supposed to foam or set in mortar. I have also seen others foamed in anyway. I would talk to an actual human at the manufacturer if you can. My experience of $90 /hr plumbers is they often do not actually check that stuff.