Bathroom Tub Challenge [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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12-23-2009, 12:01 PM

I have an partially finished bathroom that we would now like to finish. I could use advise on two items:

1. How is a tub supposed to be seated? The only thing attached was the drain pipe. There has to be more to secure the tub into position than it!

2. The walls have regular drywall on them. Should I rip it all out and replace it with cement board? We plan on tiling at least around the tub. I'd really like to do this right! Please, all input welcome!!

Photo attached.

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12-23-2009, 12:16 PM
Welcome, Ron :)

You got a good starting point there, but some questions for you:

1 - is that tub new? or a salvaged old one?

If it's new, it should have instructions. If old, it oughta rest on a framing ledger around the long wall at least. Setting that exactly right might be a chore but it's probably the best way to handle it. You can shim it from behind, so guess low if you hafta. You might could bed the tub in a wad of mortar, too, but i'm always a little wary of that method. Tubs are strong tho, assuming that's an old cast iron one. You're definitely gonna wanna get some screws against it, holding it to the framing @ the tiling lip.

2 - what have you done to investigate waterproofing membranes?

I sure wouldn't rip out a nice looking sheetrock job if I didn't hafta. You could probably Kerdi right over whatcha got there with minimal additional work & overall expense. And it'd be one of the best options for you, in terms of "how to do it right".

One caution is (similar to above) how EXACTLY the tub meets the sheetrock. You want a little overhang, which is easy on the long wall (you can notch the studs to recess the tub if needed). But you're kinda unable to do much at this point w/ the short walls - they hangs where they hangs. In fact, if anything, they really look a bit too far apart right now. Might wanna check those measurements and get back to us. You could notch in on the plumbing wall too, and then build up a "feature" on the far short wall, if you hafta, with minimal effort & complexity.

Sounds like you have a good project going - keep up the good work, keep your questions right here in this thread, and keep us posted as you go :) Merry Christmas :D

12-23-2009, 12:18 PM
Normally you put a tub in before finishing the walls as you have done. The two kohler tubs I've installed didnt need a framing ledger as Ed said, but have little plastic nailing flanges you slip over the flange on the tub and nail into the 2x4 wall framing. I also take the optional step of setting the tub in a pile of mortar. It gives it a nice solid feel. This is usually an optional step in tub installation instructions.

Also, since you have a shower, and you have drywall installed, you need to install Kerdi or a waterproof membrane over that drywall before you do anything else. No need to rip down and replace with backerboard IF you do it that way.

Also it looks like you have quite a gap on either side of the tub, you might need to rip out one side of the drywall and fir out your studs for a better fit.

12-23-2009, 12:22 PM
Welcome, Ron. :)

As I see it you're gonna have no choice but to remove the sheetrock since your tub fits loosely between the walls with sheetrock on'em. Should fit snugly to the framing so the wallboard can lap over the tub's tiling flange.

I think you'll need to fur out one or both end walls to make that work, then deal with the change in walls plane as some sorta "feature." Features are good. :)

My opinion; worth price charged.

12-23-2009, 12:24 PM
dangit, cx, i tolds'im to make a feature already :)

12-23-2009, 12:28 PM
Well, I see that now, Ed. Don't be so sensitive! :rolleyes:

Ron, make a feature like Ed said, not like I said, OK?

You feel better now, Ed? :D

12-23-2009, 01:12 PM
What are the manufacturer & model of the tub?

What are the dimensions of the tub?

What is the width of the space for the tub? :)

12-23-2009, 02:23 PM
Nah... I reckon cx has way nicer features than i gots...


12-23-2009, 04:17 PM

Thanks for your prompt and reasonably priced replies! A few more puzzle pieces and questions...

The tub looks new but its been sitting in our unfinished bathroom since we bought our house about 6 years ago (a feature). It's an Eljer that looks like a Endurocast Gibralter tub after searching a bit. Its 60" by 30". I did not see any installation instructions on their site. Our bathroom width is 61".

More questions for you...

1. Can I put cement board over existing drywall (with 1/2" shims on the side walls) or does there need to be a vapor barrier beneath it?
2. Is the Kerdi system user over regular drywall? It doesn't seem like it would have the strength of cement board as a substrate.
3. If I do go with cement board, do I need the Kerdi system too?

Please see my bathroom picture above to refresh your memories! Thank you in advance for all your good feedback! I enjoy doing things like this myself but I want it done right and want it to last!



12-23-2009, 04:54 PM
1-No, multiple layers often cause problems due to trapped moisture. Not a good idea.
2-see below & Kerdi installation instructions. Link over there --->
3-If you use cement board, you either need a moisture barrier behind it or waterproofing over it.

With 61" between drywall, you're about 2" wider than needed. I'd slide the tub tight to the plumbing wall framing and the back wall framing, leaving 2" at the head end. May need to cut some drywall out. I set all tubs into mortar for full support under the tub floor. Layers from plywood up; plastic, lath, mortar, lightweight plastic, tub. Staple lath down over plastic and adjust mortar height so the entire tub bottom is supported. I also set the back wall tub edge onto a ledger board or individual short studs nailed/screwed to existing studs.

Schluter wants regular drywall behind Kerdi, so you can leave the drywall up if you'd like and Kerdi over it. Since you've mudded & taped, you'll have to primer over it with a good primer/sealer before Kerdi.

Now, for the back wall which is 2" farther away than needed. I would probably remove drywall on that short wall up to the angled ceiling and reframe that wall to be tight to tub. Bring the new framing out to about 32-34" from back wall to make the transition easier out past the tub.

Cover the new framing with regular drywall and no mud/tape within the shower area - no primer needed either. You can mud/tape out past the glass door area to where the drywall transitions back to the side wall. :)

12-23-2009, 05:10 PM
Dana's got you covered on the construction details of your new "feature". You gotta do it that way tho, else you're ripping out a crap-ton of finished drywall and re-framing everything.

12-23-2009, 05:17 PM
BTW Ron, you a drywall finisher? That finish looks perfectomente. :)

12-23-2009, 06:41 PM
Will kerdi on drywall support his tile on the 45deg pitch and the ceiling?

I'm considering Kerdi, depending on the extent of my project and am wondering if you experts could tell me whether Kerdi is able to be used on ceilings or this 45 degree pitched ceiling/wall? With just a few nails holding up the drywall, then adding the weight of the tiles, could the drywall fall?


12-23-2009, 07:36 PM
Not the slightest of concern over that, Chris.

Tho I'd probably not bother putting any Kerdi on the sloped surface at all... It'd be plenty to just have it up the vertical surfaces to the elevation of the showerhead. That little bit of sloped area on the far left wall ain't gonna see enough water to really care much, I'd think...

Houston Remodeler
12-23-2009, 08:03 PM
I would kerdi the ceiling but I am a belt-and-suspenders kind of guy. At least use a liquid applied waterproofing such as redgard or hydroban. Once you get the hang of installing the kerdi, you can easily tackle the ceiling. For the price of the kerdi its cheap insurance.

Along with the ledger board on the long wall, you can also use expanded foam to set the base of the tub instead of a cement / mortar bed. The trick would be getting the foam into place as you'd need to be able to get your hand down there. But as you should have some drywall down, that shouldn't be a problem. Just put your arm down between the studs. A cement bed is classic tub setting, but a bit more work for a non pro. If the tub is easy to handle in the weight department, then you will need to weight the tub down with 100 pounds of something while the foam sets. Use the foam in the blue can which is much denser and less expanding than the black can. One can should do the trick. Foam also holds less "cold" than cement so the tub will warm up faster with foam than cement.

Note to physics nerds; Yes I know about the cold comment. There is only absence of heat :blah:

01-16-2010, 10:46 AM

I've taken down the drywall, seated the tub, and have installed cement board to accept new tile.

I have a question about taping the joints. Is it good practice to fill in behind the tape?



01-16-2010, 11:30 AM
I find it easiest to just lay the alkali-resistant mesh tape dry, and then make sure the thinset is loose enough to mush thru and fill those voids sufficiently.

Lookin good otherwise :)

Houston Remodeler
01-16-2010, 11:37 AM
I like to fill the joints first then put the mesh tape on top because I have a harder time getting enough thinset to ooze through. Plus the wet thinset helps hold the tape onto the wall before the top coat comes on.

01-16-2010, 02:59 PM
For the 1/8 gaps that most board manufacturers recommend, I typically use the self sticking tape and stick it on the board first, then mortar. Prebend any tape going into corners and you'll be happier.

For larger gaps, like it looks like you may have, you may want to pre-fill those with thinset mortar and allow to dry. That would allow you to go over them again if needed before taping.

01-22-2010, 08:32 PM
I put felt paper behind the cbu of the tub.

In doing some more reading on this forum I am wondering if I have created the dreaded moisture sandwich? The 45 degree wall/ceiling is roof and the left wall has eave on the other side. So my roofing felt behind the cbu backs up to the kraft paper on the insulation of the eave to the left and the 45 as well as the ceiling...

problem? should I have slit the kraft paper? I can access the insulation in the eave easily enough as well as above/attic.

Thanks in advance.

01-23-2010, 10:40 AM
Attaching some pix.

After looking at this thread
I'm fairly certain that I need slits for the insulation that backs up to UNheated space, but would appreciate confirmation before I start.

Attaching some photos. Some of the paper is already slit for me.;)
The unheated space is on the left wall, the 45 degree wall and the roof.

Do I need slits in the insulation (had extra that I added for sound insulation) that backs up to heated space or is it unlikely to be a problem without a temperature difference?


01-23-2010, 11:13 PM
The principle is the same on interior or exterior walls, Ron. The temperature differential may be more or less, depending upon your climate, but we're dealing primarily with a moisture barrier rather than a vapor barrier.

There is less likelihood of a problem with the use of roofing felt than would be the case with poly, but it's still something I would avoid if possible.

I would defeat the Kraft barrier if you still have access to it, but I don't think I'd take down my installed wallboard to do that.

My opinion; worth price charged.

01-24-2010, 10:23 AM
I appreciate your response. I live in South Carolina, the land of hot and sticky summers.

I would also like to avoid a problem and build something that will last.

I'm actually leaning towards tearing out to be sure. In hindsight I realized that I could have put the cbu flush with the ceiling instead of having the lip on the ceiling to match the walls as. So I was going to add another layer of drywall in the dry part of the bathroom to be flush. Given this twist, it might be almost as easy to remove part of the cbu, address the moisture barrier and put the ceiling and 45 back in flush.

Am I better to remove the insulation on the inside walls or just mess up the Kraft paper it?

Would the redgard over the cbu have been a better choice than the tarpaper?

Any better ideas?

Thanks again,

01-24-2010, 10:38 AM
I put fiberglass batt insulation in all bathroom walls as a sound reduction measure. Kraft faced except where an additional moisture barrier for a shower will be installed.

A surface-applied waterproofing in lieu of the moisture barrier behind the CBU would not mitigate the potential problem of trapping moisture. It would just have a larger space (thickness of wallboard) in which to accumulate. The waterproofing would also have a lower vapor transmisson rate (permeability) which could exacerbate the potential problem.

My opinion; worth price charged.

01-24-2010, 11:07 AM
Am I crazy to tear out or is this the only way to be sure I don't face moisture problems?

If I'm going to do tear out, is this the best approach: all insulation around wet areas, remove Kraft paper, then hang tar paper, cbu, thinset, tile?

Dry areas to be tiled will have insulation with Kraft paper on heated side. No Kraft paper where it's just for sound insulation. No tarpaper for dry areas. Then cbu, thinset, tile, done.

While I'm at it, should I go ahead and replace my gray drywall with greenboard? (Bathroom has been unfinished since remodel in 2000, before we purchased) All I saw at my HDepot was purple??


01-24-2010, 03:26 PM
f I'm going to do tear out, is this the best approach: all insulation around wet areas, remove Kraft paper, then hang tar paper, cbu, thinset, tile?

Best approach would be surface waterproofing like Kerdi, HydroBan or similar. Otherwise, your plan looks good.

I wouldn't say your .... "crazy"... just being extremely thorough. :) If it's gonna make you lose sleep, then go ahead and do it. When I rebuild tub/showers and showers I typically remove any facing found on insulation. No need for facing on interior walls IMO. I only use regular drywall on my projects. Over that, I typically use quality paints including PVA primer and multiple coats of semi gloss finish. There's a place for all the various special boards out there, but not in a typical residence IMO.

Insulation facing goes towards the "conditioned" side of the wall, either heated or cooled typically. If both sides of the wall are interior, then I'd recommend unfaced insulation.

01-25-2010, 08:15 PM
Maybe I should ask this way- what could happen if I don't remove my insulation facing? Am I crazy not to remove it? I can still access it easily for the outside walls- are they more likely to be a problem? Removal of facing on inside walls will require some tearout... but if it's likely to cause a problem, it's easier than tearing out tile down the road...

Any input appreciated from this friendly forum,

01-26-2010, 06:16 AM
Go ahead and remove/defeat the kraft paper facing. You are not crazy to do it. Instead, doing it will keep you from worrying yourself crazy.

There, you feel better already, right? :D