Hi,

I'm going to be re-doing my existing tub/shower area as part of a complete bathroom reno.

I'm planning to use kerdi on the walls of the shower. Even though I understand it's not necessary, I thought I would use fiberrock behind the kerdi. Mostly, I'm worried about some water getting into the wall where the fixtures stick-out, so I figure if some water does get in then the fiberrock will stand up better.

I'm not planning on tiling the ceiling - I'm going to paint that. I also intend to use fiberrock on the ceiling. In this case, I believe the fiberrock will paint better than CBU.

Questions:

1) Is it ok to not tile the ceiling? I'm used to showers being 100% tile. Note: The shower head will be vertical mount down from the ceiling.
2) I know that a vapour barrier is not necessary behind the walls (because of the kerdi), but what about on the ceiling?
3) Will I have any trouble painting the fiberrock?
4) Do I need to mud/tape the fiberrock walls? (ceilings, obviously yes).
5) How good is fiberrock? Is it impervious to water, or just resistant? Is there another paintable option that I should consider?

Bonus Question: I've read a lot of posts on this board about using mortar, or spray-foam under a tub. I've also heard people say you don't need anything at all. Can someone sum this up for me? My tub is a 60" soaker tub. It's an above-floor-rough type tub. I want to do the right thing but I can't figure out what that is.

Thanks!

When you buy a kerdi drain now, you get a couple of extra items now: two rubber rings surrounded by two inches of Kerdi. One is made to fit around the shower valve, the other around the shower head supply.

If you didn't get these with your drain, you can order them. Of course, in your case since the shower head is coming from the ceiling, you won't need the rubber ring for the shower head.

Having said all that, there is really no reason to waterproof anything above 6 1/2 feet. No significant amount of water will get that high. The last shower I tore out was built with green board and the highest moisture I found was about three feet from the floor.

You can tile the ceiling if you want, it's not necessary. A good quality paint on the ceiling will protect it just fine. Save your money on the fiberock and get drywall. It's easier to install, cheaper, and fiberock is only water-resistant anyway. Trust Kerdi to do its job and don't worry about it. You don't need a vapor barrier in the ceiling.

For your tub, you should check with the manufacturer and see what they require for support. If you can give us the make and model of it, someone on here that is familiar with it might be able to tell you what is required.

Hi, thanks for the reply.

Just to be clear: It's a tub+shower combo, not separate. I don't think that will affect your answer at all, but just in case. What this does mean is that I haven't bought a shower-kit, I'll be buying Kerdi by the ft and installing it.

I'm not planning on buying any of the pre-made corners/edges or anything either. I've *assumed* I will be able to make all the corners with the regular stuff.

This is the tub: http://www.azzurabath.com/single_product.php?Class=5FT%20BATHTUBS&Model=BO64

The install guide doesn't specify much in this case.

I'll comment on the Fiberock. Seriously, putting Kerdi over Fiberrock is a real pain in the bum. It sucks the moisture out of the thin set so fast, you end up having terrible contact between it and the Kerdi. Drywall is much much easier. And..as Kman said...you can buy those rubber sealent rings separately. If you caulk around the cover plate, you won't get any water behind anyway.

As Kman mentioned ... check with the tub manufacturer, but never allow the weight of the tub to sit directly onto the tiled deck.
I always support the tub legs with assorted thicknesses of plywood and then squeeze in the foam just to help support and keep everything in place (put water in the tub first)
If your tub has rails, then I use plywood and shims at the ends of each rail to level and support the weight .... then pack mortar under the center of the rails.

I too do not recommend Fiberock as your CBU for the reasons mentioned. It really sucks.....moisture. You are supposed to use regular wallboard per Kerdi directions, works perfectly!

The tub installation is very important, follow every step in the directions. Pay special attention to the "tile lip extrusion" detail, I hope you have that.


Jaz

Ok, thanks everyone. I've officially abandoned the fiberrock and I'll just use good-old-drywall (1/2").

Bri: I'll caulk around the goof-plate, but what I;m worried about is water wicking down the grout behind the plate. Shirley some must get in there? Maybe I worry too much.

As for the tub, maybe I'm confused: Is everyone suggesting that I put mortar or foam under the feet/rails just to make sure they have good contact with the subfloor? I guess that makes sense - but what I thought people were suggesting was basically filling the entire cavity under the tub with foam/mortar so the tub itself doesn't flex with weight. I've been told it makes the tub feel more solid. Comments on this?

As far at the hole for the cover plate is concerned, there are a few things you can do. Sometimes I will leave the Kerdi over the opening...just leave the hole for the tap and the screws. OR...cut the drywall so it bevels downwards(bottom of hole) and then coat it with silicone. Any water reaching there, will not soak into the drywall and will drain out instead of in. I usually use my liquid waterproofing instead of silicone...but then I have a 5 gallon pail of the stuff.

Mortar works great ... just be sure to support the tub until it sets up. Shims are helpful under the legs or rails until the mortar sets.
If you want to use foam, use it to assist keeping everything in place ... it help insulate the tub .... it does add some support under the main body of the tub (not under the feet or rails).

Ok, just to make sure: It's probably a good idea to use the blue drywall (for humidity resistance?) instead of regular drywall throughout (including behind the kerdi). Yes?

While I'm at it, some more questions for this project:

I'm going to be tiling with 1x2 polished marble subway tiles. Any tips? I was thinking of buying some sheets of 1x1 as well so I can use them to fill in the offset where I start the 1st sheets against a wall. Make sense?

I'm also planning on building a few niches, and want to make sure that I don't end up with sliver-sized tiles at the top or bottom of the wall. Any tips here? Do I need to actually stick the tile up on the wall to do a rough layout? Or can I rely on my 12x12 sheets to be actually 12x12+1/4" grout along the outside and work completely off measurements? I assume I should start at the bottom of the wall where the tub is?

Thanks a lot. This forum is simply the best thing on the internet for quality advice.

You can use the blue drywall outside the shower area, but there's no need for it behind Kerdi. If the Kerdi is properly installed, no moisture will get to the drywall anyway.

With 1x1, the toughest thing to overcome will be the build-ups caused by the overlaps of material. Some installers have gone to the use of liquid waterproofing for that very reason. One way to lessen the effect of the build-ups is to skim-coat the surface of the Kerdi from the corners so that it's more of a gradual buildup instead of just over a couple inches.

To gauge the size of your cut pieces, lay out the tile on the floor like it would be on the wall to get your measurements. But it's going to be tough with a 1" tile to avoid having small cut pieces. Some of the other guys might have better suggestions on that.

Now I'm freaked out about the overlaps. I understand the skim-coat option. Are there any other possible tips/tricks to help with this? The tiles are 1x2, not 1x1 but I don't imagine that matters much.

What size trowel should I use? The tiles are marble with paper-mesh backing. Should I deliberately apply the mortar thick in the non-overlap areas to make sure the overall install is even?

Doing a test layout of the tile is a great idea. I can't believe it never occurred to me.

For my niches, I'm thinking of doing the rough-build deliberately too large, applying the kerdi, then building up the niche so it lines up nicely with the tiles. If I need to do a large (1/2"+) buildup, I was thinking of using blue-foam insulation stuck into the mortar. Does this sound reasonable?

Thanks again. I'm getting close to my project start.

Can anyone help me with my last few questions?

Basically:

1) I want to avoid bumps in my 1x2 subways where my ditra overlaps. Any tips? Should I apply the thinset thick in the non-overlap areas?

2) If I skim-coat with thinset and let it dry, will the next layer of thinset bond to the dry thinset?

3) Does anyone see any problem with me using blue insulation foam to help build up my niche to make a perfect fit with the tile? The foam would be embedded in thinset, on top of ditra.

4) Finally: Anyone want to recommend a trowel size?

Please help!

1. You obviously meant to write Kerdi, not Ditra. Apply the thin set uniformly. Use a wood beating-block or a rubber grout float to beat tiles in.

2. Yes, you can skim then go back with the bond coat.

3. I guess that would work.

4. For Kerdi the recommendation is now 1/8" square notch. The old spec was 3/16x1/4" V. The trowel for your tiles can be similar to the Kerdi, or maybe a bit larger. All depends on how thick they are.

Jaz

Thanks Jaz,

The mosaic tiles are marble, and are relatively thick: 1/4".

I almost always do my niche bottoms with 3/4 inch counter top stone. If you have a counter top place in your area they will usually have a garbage can full of scraps. If you are lucky you will find a piece of marble to match yours. That way it does not really matter how it lines up with the tiles.

Ok - on to the next question. I've attached two photos of my marble tiles.

They are 1x2 subway in a brick-pattern.

How do I stick these on the wall? I sort-of assumed I would put them up interlocked, but the mesh will get in the way. Do I instead put them on the wall lined up (like in photo #1) and then go back and fill in all the missing tiles?

They also seem to have both a mesh and paper backing. I assume I leave both on?

Thanks!

Spacecadet, Your photos will not show up as you have posted them.

You can either host them to an imaging site or use the web site forum under "Post PHOTOS of the project you're having trouble with"

The mesh backed tile should not have any mesh getting in the way. The sheets are interlocking. Separate pcs will have to be placed at cut outs or end of walls etc.

I have never seen subway tile with paper backing. Usually paper or clear plastic is only on the face side of some mosaics.

I've run on to a few of those. The paper is usually wax-coated and placed on the back of the tile sheet to keep the mesh from "imprinting" the face of the tile below it during shipping.

Ok, let's try the photo's again. Kinda weird, the download links worked fine when I composed the message.

Marble Tile 1

Marble Tile 2

Hopefully it works this time. As you can see in the photos, the tiles can't interlock with me removing some of the mesh first.

The second photo shows the backing. The paper backing is attached to the tile, with the mesh then attached to the paper. So, in the box the mesh will contact the face of the tile below it. The mesh is somewhat "stuck". Perhaps the mesh is protecting the tile below from the wax on the paper?

The photos came thru this time.
Your right, the backing will need to be cut away.
Too bad you didn't post a photo of the back so we could see what your talking about.
Usually there is one or the other type of binding on the back. I have never seen where it has both.

If the mesh seems very well attached then carry on with the installation.
Word of caution, paper backed mosaics fall apart when cut on the wet saw. Maybe that's why they added the mesh.

Photo of the tile-back is here: Tile Back

The mesh is on pretty good. It's obviously glued on.

Do you really think it'll be easier to cut-out the mesh, rather than installing the tiles square and filling in the blanks with individual tiles (know what I mean?)?

Thanks again for all the advice.

It's up to you. A lot easier to cut out mesh and interlock the sheets than to cut out a bunch of separate pcs from another sheet and try to strip mesh and paper from those pcs so there's no lippage.

Well since I've never done this before and you have, I think I'll try it your way

Thanks again!

One new question:

My shower wall tiles are 7 3/4" x 11 3/4" ceramic. Can I use my 1/4x3/16" V notch trowel for this (which is the trowel I'm using for the kerdi).

Thanks!

No, you will need at least a 1/4x1/4 or a 1/4x3/8
Use the latter if the ceramic has a fairly pronounced lug pattern on the back. Over Kerdi I would also suggest you back butter the tile with the unmodified thinset.

Ok, here's (I think) a tough one then:

I built up a test-board to figure out the thickness of my finished wall. So, I took 1/2" drywall, thinset, kerdi, thinset, tile.

The thinset for the tile, as I mentioned above, was using the 1/4x3/16" V notch trowel. My test finish wall ended up approx 7/8" thick.

If I switch to the 1/4x3/8" (square notch?), how much do you think that will affect the finish-wall thickness?

Thanks again.

Why does it matter when its on a wall?
If you got 80% coverage with the v notch trowel, then use it.

Two of my shower fixtures have to be installed "just-right" and don't have cover-plates or anything to make install easy.

Both will be attached using brass-nipples, and I want to make sure I get the right length the first time.

So, I made a test board (described above) that I'll use to judge how far the plumbing will protrude before I put up the finish wall, but that was done with the other trowel.

I assume with the 1/4x3/8" trowel, the tile will sit a little higher, but I wonder if you have a guess how much?

I'll still use my existing test board when doing the plumbing, but I'll adjust for the expected extra thickness. I'd assume it would be something small like 1/16", but that might push me up a size for the nipple.

It's very rare that a stock nipple will be just right. I make custom brass nipples for all my jobs that have body sprays etc.
They are easy to do if you have the right materials.

Most plumbing fixtures that have nipple attachments with escutcheon covers usually have an adjustment range up to 3/8" or more. Same with the main valve trims.

You should try and post some photos. Thats always helpful.