It's funny, but I was thinking of asking a similar question. I know that there are several acceptable types of waterproofing, and not every contractor likes each one. What I wanted was an exact list of steps for each type, i.e.. poly behind cement board, Kerdi board, etc., what type of tape (if needed for that type) so that I can ask each contractor to give me pricing with ALL the steps spelled out so that my expectations are met and there are no surprises. I've read enough of this board that I have a good idea, but I'm afraid that I might leave out a step.....and so might the contractor.

You can either put poly behind the cement board, or you can use a surface membrane like red guard / hydro ban (there are many others) Do not use poly and and surface membrane, one or the other. If you use poly it has to overlap the tub or pan. Screw the cement board with the special screws, tape and apply thinset over the seams. Don't make it too thick, feather it out. When dry, I used a 3M sander and cut down any thin set. If you don't do this, you may have a lump in your tile.

For surface membrane, I use 100% silicone, between the gap of the cement board and the tub.

I'm just a DIY'er. I've done 3 showers and a tub - and haven't had any problems - I use the surface membrane.

Using a surface applied membrane like RedGard?

In that case, read the RedGard (or whichever membrane you are using) instructions first, before anything gets installed.

Install cement board over the studs. No 6-mil poly is needed since you're using a surface applied or a topical membrane like RedGard.

If using standard-size wall tile, I'll install the cement board as previously described; directly to the studs and held slightly above the top edge of the tub flange.

If installing a small mosaic tile on the walls, I might attach furring strips to the faces of the studs, then install the cement board to the studs/furring strips so the cement board covers the vertical portion of the tub flange, with the bottom edge of the cement board gapped just above the flat portion of the tub's rim. That'll give the bottom course of the small mosaic a firm backing from the cement board.

Treat the seams between the cement board sheets as defined by the installation instructions for the membrane that you are using. Different manufacturers have different requirements. Some membranes require fabric or another type of reinforcement at the seams, others don't.

There are also coating thickness requirements for the membrane. It'll all be in the instructions.

When the membrane has cured, tile over the membrane.

Grout, etc.

The common thread that I tried to include in the descriptions?

There is installer leeway in terms of personal technique. But the installation instructions for the various materials should be followed. Watch the cement board fastening schedule and adhere to the specific membrane installation instructions.

Good luck.

Thanks all. This was exactly what I wa looking for!

If you don't mind, I have a few more questions....

1) I'd like to have vinyl beadboard planks installed on my (bathroom) ceiling (over greenboard/sheetrock). Could there be any issues (moisture) with this down the road?

2) Re my bathtub install (alcove style). Install instructions say to set in a mortar bed. Should I have heavy poly put down on the floor, then the mortar, then another sheet of poly? It seems to me that moisture from the mortar would seep into the plywood subfloor. I also read somewhere that it's a good idea to put plastic over the mortar as well in case the tub ever needs to come out.

3) I know everyone probably has their favorite - any thoughts on grouts? Fusion (stain proof/color perfect - single component) or Polyblend? I like the color choices they offer better than those of Mapei.

We're not doing this job ourselves, I'm just trying to be an educated consumer. While I won't be standing over the contractor & subs, I just want to have a good understanding of how things should be done.

Thanks!

I would like to get something clarified. Our contractor put up cement board with no plastic vapour barrier behind. It is correctly placed just above the tub flange which is also screwed to studs. I have applied the mesh tape and 2 coats of Redgard to the cement board. Contractor says the cement board does not get a silicone bead between it and the tub flange. I read that it does. We are not past the Redgard stage yet and I certainly can seal the cement board to the tub flange if I am supposed to. They did the gut construction job but we are in charge of tiling our floor and dealing with tub surround. We are having a quartz solid surface tub surround which will be caulked to the tub. Probably Redgard is overkill but since we do have corners and niches, I wanted it applied.

I thought it did too silken1. Maybe MongoCT or geofrrey can give us some answers.

There was a time when I didn't know any better that I thought there was no need to seal the gap between the cement board and tub flange too. Yes, at a minimum a bead of silicone will work. It's probably overkill, but I usually use a silane or urethane sealant like Sika or Kerdi Fix. Those are really beefy.

Since the tile comes down, over the gap between the cement board and tub - it would be very difficult to get water in there. But I caulked it, it's $6 for a tube. You have the remember contractors do the very minimum - to maximize their profit.

I don't mind the money or doing it. Just want to be sure it is the correct thing to do. I can't see how it could be bad to do, but all this humidity and double vapour barriers etc. I guess a person could get it wrong if they don't know. My builder is very good with most stuff which is why I was surprised when he said it shouldn't be caulked.

I really don't think it's an issue - either way.

No right or wrong. He probably has just always done it that way. I prefer to use the caulk.....

Avanti - could you weigh in on my 3-question post above (re ceiling, tub, etc). Thank you!

1. No problem I can see with this. Caulk the edges.

2 Setting the tub in morter, if slab, no plastic needed. If plywood, you can use a liner on the floor. On top of morter, really no need.

3. I'm a big fan of Fusion Pro. Use a small paint mixer to blend it up and it softens the grout a bit. Lightly dampen the areas you're working on. Only do small areas at a time, don't let it "dwell" on the surface for more than a minute or two, tops. Take a well wrung-out sponge and go over the area in a circular motion, then clean out the sponge and gently wipe diagonally across the tile, flip sponge and continue next wipe. An hour or so later, you "may" need to take a barely damp microfibre cloth and buff the tile....finish with a dry cloth, if needed.

"We're not doing this job ourselves, I'm just trying to be an educated consumer. While I won't be standing over the contractor & subs, I just want to have a good understanding of how things should be done."

Do you even know if they are using cement board at all? My tub surround was floated with cement. Why not ask your contractor to spell out the procedure they'll be using in the contract/agreement? IMO, if you want to know what your contractor will be doing or what methods he'll be using, the time to ask him is before he starts doing it.

jellytoast - yes, they are using cement board and we have discussed products and procedures. I just wanted to get input/confirmation from others.