My bathroom remodel

[sugaree53]

Ok I bought my 1st house --an older one (late 40s). I am 58-woman--hear me roar! I have been doing all the remodeling myself with great success so far. Now to the bathroom--there was old linoleum floor and wall tile which i tore out--it was black/white checkerboard and reminded me of the Indiana 500. The old sink didn't work and the old tub was replaced as well-it had a leak. I want to lay ceramic 12" tile on the floor and 6" on the walls except around the tub where I want to create a mosaic mural on the 3 walls. The sub-floor is oak hardwood and in good shape. Do I need plywood over it before I put the hardi board? Do I absolutely need to add a moisture membrane like those kerdi sheets? ..... Now on the walls there are remains of an old tile installation that was removed. I can see some old mastic. Can I leave the existing drywall up which has been covered with joint compound in most places and then cover it with the hardi board then tile over that or just tile directly onto the drywall with just some sanding to get it smooth? This is for the mosaic part I plan to do. This is a very small bathroom and I want to cut costs however I can--thx

[bbcamp]

Hi Cindy!

The sub-floor is oak hardwood and in good shape. Do I need plywood over it before I put the hardi board?

Yes. 1/2" minimum.

Do I absolutely need to add a moisture membrane like those kerdi sheets? .....

Your tub surround needs to be waterproofed if it has a showerhead. There are a number of ways to do this.

Now on the walls there are remains of an old tile installation that was removed. I can see some old mastic. Can I leave the existing drywall up which has been covered with joint compound in most places and then cover it with the hardi board then tile over that or just tile directly onto the drywall with just some sanding to get it smooth? This is for the mosaic part I plan to do.

It will be cheaper to tear down the old drywall and install backerboard with a plastic sheet behind it for waterproofing.

[Tool Guy - Kg]

Originally Posted by sugaree53

The sub-floor is oak hardwood and in good shape. Do I need plywood over it before I put the hardi board?

Yes. Absolutely...solid dimensional wood expands and contracts too much and you need plywood to insulate the stiff tile from this movement. I'd recommend removing that oak finished floor so you don't gain so much thickness when you add the ply.

Originally Posted by sugaree53

Do I absolutely need to add a moisture membrane like those kerdi sheets?

If you're using Kerdi to waterproof the walls, then you don't need a moisture barrier behind the substrate you're applying Kerdi to.

Originally Posted by sugaree53

..... Now on the walls there are remains of an old tile installation that was removed. I can see some old mastic. Can I leave the existing drywall up which has been covered with joint compound in most places and then cover it with the hardi board then tile over that or just tile directly onto the drywall with just some sanding to get it smooth?

Oh...geez...that's, well.....
Let's ask more questions to get a better idea of what's going on here and what you're trying to accomplish. Is this for the area inside or outside the tub....or both? Is the tile going up to the ceiling? Adding to the walls will thicken it up and this can cause a problem on the tub where the back "shoulder" of the tub is comparably thin....and this extra thickness typically means you need to address the edge of the tile so you don't see the Hardibacker? Is this a lath and plaster wall that you're trying to avoid removing? What do you see as the reason not to simply remove the walls and replace them with drywall?