Home>Discussions>BATHROOMS>Bathroom Sub-floor Re-Build Tub Installation
4 posts / 0 new
Last post
Bathroom Sub-floor Re-Build Tub Installation

Just registered, first post... please forgive my ignorance of terms etc.. I'm a DIY just starting my research.

We hired someone to demo our upstairs bathroom in a 1977 built home. Cement "Mud?" floor and all down to what appears to be a 1/2" piece of plywood "base" which the cement/mud floor was originally placed on.

I'm planning on rebuilding the sub-floor with 3/4" plywood (floor rated), and 5/8 cement backer board (mortar & screws etc.) for preparation of 3/8" thick porcelain tile which should be the proper height to have tile flushed with the toilet flange.

My question is regarding the alcove kohler cast iron tub and the sub-floor underneath. I don't believe the cement/mud floor was poured underneath the original tub (missed that part of the demo). I do see the tub had a "leveling stringer" attached to the wall joists.

Not sure if the front of the tub was placed on the edge of the cement/mud floor or if it was placed directly on 1/2" piece of plywood sub-floor, directly over a floor joist.

Anyhow, I'm just wondering... When I'm rebuilding the sub-floor do make the ENTIRE room floor height the same? Do I place the cement backer board underneath the tub area for it to "rest" directly on and then tile up and around the front using silicone between tile and tub?

Thanks a million,

PS- I realize there maybe a number of other questions needed to assist on the answer. Fire Away. I'm trying to do this correctly but realize that no matter how much reading/research I do... It doesn't replace true experience and I appreciate yours.

Re: Bathroom Sub-floor Re-Build Tub Installation


The 3/4" plywood needs to be exterior glue (as opposed to exterior rated) CC or better. NO CDX, NO sheathing.

The 1/2" ply can be removed (probably a good idea) or if it stays it needs to be properly secured before the new plywood gets installed.

For all things tile related, start a new thread, with pictures, on the John Bridge Tile Forum. There you can use the handy dandy deflecto-lator to see if your floor joists are capable of handling tiles.

On the JBF is also an extensive library rich with info.

Re: Bathroom Sub-floor Re-Build Tub Installation

To better understand what you need in a subfloor for tile, go to JBF as recommended. You'll find all your answers there.

Re: Bathroom Sub-floor Re-Build Tub Installation

The question of tub height arose- I don't know if JB will cover that. Some tubs have a detail at the bottom which will make fitting tile neatly a bugger if it's too low. If that's a problem then it needs to be raised to backer level on waterproof substrate (not backer itself). If not, I seen no real need to raise it, but it would probably look better raised up- you make that call yourself, knowing that it's then going to be adding some plumbing work to the mix. Personally I'd also consider how well the tub is supported now and if I felt additional flooring would improve things then I'd do it. I've seen my share of sinking tubs and that fix is a lot easier now than it would be later.


Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.