None of the tub walls are exterior walls so we just planned on using the hardiebacker and then tiling. Is that ok? Do we need to do something else?

You need either a plastic moisture barrier behind the Hardie or a surface waterproofing on top, like Red Guard or Kerdi. The backer board won't be harmed by water, but like tile and grout, it is water resistent, not waterproof. Water can and will get behind the tile, grout and cement board, so you need something to protect the studs.

I am wondering about what thinset is best to use under the hardieboard on the floor?

I prefer laticrete's megabond at Lowes, but Custom's Custom Blend At Home Depot will work, as well.

Can we use this same thinset between the hardiebacker and tile?

No, you want a modified thinset to actually set the tile. From Lowes, Laticrete's multi-purpose thinset is the better choice, but Custom's Versabond at Home Depot will also work.

We have 1/2" subfloor and are installing new 1/4" OSB on top of that as well before the thinset and hardieboard.

Instead of 1/4" OSB, make it 1/2" plywood. If your floor really is 1/2" (and I believe it may actually be a little more, like a shy 5/8")1/4" won't help at all. Additionally, 1/4" wood based underlayments tend to delaminate under ceramic tile.

terriks

"You need either a plastic moisture barrier behind the Hardie"

What exactly do you recommend for this? How do we install it to the studs? We plan installing the tub in some mortar as well and will be using some plastic in that process. Can we use the same for this?

Bill,

Thanks for the information. We will scrap the 1/4" OSB and get some 1/2" ply instead. Should it be exterior grade? We had to remove the subfloor that was under the old tub so we are down to the joists there. What should we put under the tub? The same? Do we need hardieboard under the tub as well? We are installing a Sterling Ensemble tub-Vikrell material. We plan to use the mortar bed install method.

Do you have any experience with the Mapei grout and grout maximizer that we are planning to use? Should we stick with something from the same brand that we get the thinset? We are thinking of going with the Laticrete from Lowe's since we have a gift card for there.

What do you recommend for a grout sealer?

Any tips on getting the subfloor and hardieboard tight to the toilet flange? We have an old cast iron one that will be staying in but we want to make sure to build the subfloor up to it.

Again any and all help is greatly appreciated!

April

April-- The plastic can be either 6 mil polyethlene (which can be found in the paint aisles at HD or Lowes, or 15 pound tar paper (in the roofing area). Just staple it to the studs, and make sure the bottome edge sits over the tub's flange against the studs.

We will scrap the 1/4" OSB and get some 1/2" ply instead. Should it be exterior grade?

Absolutely. BC or AC exterior grade. It really shouldn't be CDX because there are too many voids in it.

We had to remove the subfloor that was under the old tub so we are down to the joists there. What should we put under the tub?

You should have exactly the same subfloor under the tub as you do under the hardi board in the rest of the bathroom. No need for the Hardi under the tub, though. The ONLY reason for the hardi is a more stable bonding surface for the tile thinset.

Do you have any experience with the Mapei grout and grout maximizer that we are planning to use?

There's no need for the "maximizer". Read that as taking money from those who don't know better. These grouts are already modified. But these places are trying to maximize their profits, capitolizing on the "stainfree" thing going on. All that maximizer is, is a liquid latex additive, and that would be fine for a grout that's not modified yet. To the best of my knowledge, the only company that even MAKES an unmodified grout any more is Hydroment, and they're pretty hard to find. The laticrete grouts they have a Lowes are every bit as good as the Mapei (and as far as I'm concerned, better), but even there, they will try and talk you into using a grout additive. Don't waste the money.

What do you recommend for a grout sealer?

Rather than type it all out, I'll let you ckeck out my FAQ on the gallery side of this forum, and that'll explain my stance on grout sealers.

Any tips on getting the subfloor and hardieboard tight to the toilet flange? We have an old cast iron one that will be staying in but we want to make sure to build the subfloor up to it.

you really want that flange to be sitting pon top of the subfloor, at the very least, if not on top of the hardi board. If it doesn't, you're going to have leakage of the STANKY kind.

One more question...how do we handle the tile to tub line? We used the 6mil poly vapor barrier, silicone caulked to tub flange about 1/4" from the tub line, brought the hardieboard to the same point (used furring strips to make everything line up). We plan to bring the tile to about 1/8" of the tub line...what should we do between there? Do we want to caulk the tile to the tub line? Do we need weeping holes? How will that look if we are caulking the tile to the tub? Should we try and put the caulk up behind the tile (kind of by the hardieboard edge) or touch the caulk from the edge of the tile to the tub?

Caulk the gap between the tile and the grout. You can get color- and texture-matched caulk to match the grout. In essence, the line of caulk will look like a line of caulk.

Weep holes are not required. "Because", that's why. lol.

Oops. Should have written "Caulk the gap between the tile and the tub."