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Old 02-09-2011, 03:08 PM   #1
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Cement board at tub lip


I've read posts that say:

=====
1. Install spacer strips on the wall studs to allow the cement board to overlap the tub lip and that this is a MUST for waterproofing. Stop the cement board 1/4" above the horizontal surface of the tub and stop the tile 1/8" above the tub.

2. Run the waterproof membrane that is behind the cement board over the lip of the tub and stop the cement board above the lip of the tub. Then install the tile over the tub lip to 1/8" above the horizontal surface of the tub.

3. In either case, some say to fill the gap between the lip of the tub and the cement board or tile, with thinset.
=====

I'm wondering why would it be necessary to run the cement board overlapping the lip of the tub as in recommendation #1? And that recommendation #3 is a really bad idea.

Wouldn't recommendation #2 be perfectly adequate for full waterproofing? Wouldn't the tile be strong enough to overlap the tub lip without a cement board backing? Also, it seems that recommendation #3 is really bad as it would allow any water that leaked past the caulk between the bottom of the tile and the tub, to wick up and cause mold or water damage.

It seems to me that doing recommendation #2 and just leave air space behind the tile with just caulking between the bottom of the tile and the tub would be the optimum way to install the tile. Plus it would negate the extra work and expense of installing spacer strips on all of the wall studs.

Which way do you recommend doing it?
HRG


Last edited by Homerepairguy; 02-09-2011 at 03:11 PM.
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Old 02-09-2011, 05:27 PM   #2
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Cement board at tub lip


1. Never done by anyone on purpose---no way to match the 1/2 inch drywall to 1/2 inch backer board-
That would be a mess.

2. Waterproof membrane does not go behind the backer board--it is applied to the face and tile is set to that.

If you are talking about the sheet of plastic some people apply to the studs as a vapor barrier --I don't do that so I don't have a suggestion on that.

3. You need to fill that void in order to grout---if not you will keep packing the crack with grout and never get the job done right.

Remember---studs tight to the tub---walls flat---backer starts at the top of the flange.

HydroBan is your insurance----Mike---

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Old 02-10-2011, 03:51 AM   #3
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Cement board at tub lip


Quote:
Originally Posted by oh'mike View Post
1. Never done by anyone on purpose---no way to match the 1/2 inch drywall to 1/2 inch backer board-
That would be a mess.
My description for item-1 was not clear enough. There's no drywall involved. The install would consist of:
- Alcove tub (Americast in my case) installed with lip of tub held against 2x4 studs using roofing nails or similar.
- Furring spacer strips nailed to 2x4 studs. Thickness of strips such to allow mounting cement board straight down over the tub lip.
- Felt or other vapor barrier attached over furring strips.
- Cement board installed over vapor barrier and extending straight down over tub lip (because of the furring strips), stopping 1/4" above the tub.

Quote:
2. Waterproof membrane does not go behind the backer board--it is applied to the face and tile is set to that.

If you are talking about the sheet of plastic some people apply to the studs as a vapor barrier --I don't do that so I don't have a suggestion on that.
Yes, referred to the vapor barrier applied to the studs as the "waterproof membrane".

Quote:
3. You need to fill that void in order to grout---if not you will keep packing the crack with grout and never get the job done right.
I was thinking that in the recommendation #2 method, the cement board would be about 1/4" thick. I read that the Americast tub lip is 1/8" thick. So the top surface of the cement board would extend 1/8" past the tub lip. Then the tile installed over the cement board. Would that amount of void still be too much for the grout to handle?

Quote:
Remember---studs tight to the tub---walls flat---backer starts at the top of the flange.

HydroBan is your insurance----Mike---

Last edited by Homerepairguy; 02-10-2011 at 03:54 AM.
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Old 02-10-2011, 06:34 AM   #4
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Cement board at tub lip


1/4 " backer board is for floors--not to be used on walls-----

You are way over thinking this. Tens of thousands of tub surrounds are built with the method I described.

Why would you want to use 1/4 " backer and furring strips?---way more work than the tried and true Method.

Do let me know how your job comes out with the new method.----Mike----
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Old 02-10-2011, 02:15 PM   #5
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Cement board at tub lip


Quote:
Originally Posted by oh'mike View Post
1/4 " backer board is for floors--not to be used on walls-----

You are way over thinking this. Tens of thousands of tub surrounds are built with the method I described.

Why would you want to use 1/4 " backer and furring strips?---way more work than the tried and true Method.

Do let me know how your job comes out with the new method.----Mike----
Being a novice in tub/shower tiling, I was mistaken in thinking that the cement board would be 1/4" thick. I will use 1/2" thick cement board.

If I understand the method you described, it is:

1. Tub installed tight to 2x4 studs.
2. Half inch cement board directly on studs, stopping on top of tub lip. No vapor barrier behind the cement board.
3. Hydroban coating on the cement board.
4. Install the tile on the cement board, extending down over the tub lip to about 1/8" above the tub horizontal surface. The void between the tile and tub lip is filled. What do you recommend to use to fill the void?

Sorry if any of the above is not what you meant. Thanks for the help,
HRG

Last edited by Homerepairguy; 02-10-2011 at 02:44 PM. Reason: Changed Hydrostop to Hydroban
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Old 02-10-2011, 02:25 PM   #6
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Cement board at tub lip


You have it! The void is filled with thinset (modified) as you set the tiles.

Use tile mesh on the cracks and corners,before you apply the Hydroban--the Hydroban is thick enough to fill the holes in the mesh.

Some like to fill the mesh with thinset--just like taping drywall--this is a good method also.

Thanks for putting up with my snappy answer,before.---Mike---
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Old 02-10-2011, 02:47 PM   #7
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Quote:
Originally Posted by oh'mike View Post
You have it! The void is filled with thinset (modified) as you set the tiles.

Use tile mesh on the cracks and corners,before you apply the Hydroban--the Hydroban is thick enough to fill the holes in the mesh.

Some like to fill the mesh with thinset--just like taping drywall--this is a good method also.

Thanks for putting up with my snappy answer,before.---Mike---
No worries! I really appreciate your taking the time to help. Would have been a disaster if I had used 1/4" cement board.

HRG
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Old 02-10-2011, 04:56 PM   #8
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Cement board at tub lip


You would have realized that the stuff was to springy when you were installing it.

By the way--I prefer Durrock or Wonder board over Hardi Backer--Hardi can suck the water out of the thinset leaving a weak bond. It is a very popular product--it may just be me--I tried the stuff many years ago when it first came out--didn't like the results and never tried it again.

I do a lot of bathrooms----17 last year--total guts--I speak only from my experiences.--Mike--
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Old 02-10-2011, 05:06 PM   #9
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Cement board at tub lip


Quote:
Originally Posted by oh'mike View Post
You would have realized that the stuff was to springy when you were installing it.

By the way--I prefer Durrock or Wonder board over Hardi Backer--Hardi can suck the water out of the thinset leaving a weak bond. It is a very popular product--it may just be me--I tried the stuff many years ago when it first came out--didn't like the results and never tried it again.

I do a lot of bathrooms----17 last year--total guts--I speak only from my experiences.--Mike--
I will go with Durrock or Wonder board, which ever is available in my location. Thanks for that additional tip.
HRG
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Old 12-05-2011, 04:04 PM   #10
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Cement board at tub lip


Quote:
Originally Posted by oh'mike View Post
You have it! The void is filled with thinset (modified) as you set the tiles.

Use tile mesh on the cracks and corners,before you apply the Hydroban--the Hydroban is thick enough to fill the holes in the mesh.

Some like to fill the mesh with thinset--just like taping drywall--this is a good method also.

Thanks for putting up with my snappy answer,before.---Mike---
Mike, any pointers on how to fill the void with thinset? Would you recommend, back-buttering the tile with enough thinset to fill the gap, or put the thinset directly on the lip and place the tile? I'm having trouble wrapping my head around the best way to approach this. Thanks!
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Old 12-05-2011, 05:30 PM   #11
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Cement board at tub lip


I just pack that void with the flat side of my tiling trowel---leaving that flush with the face of the board---then trowel the face of the board and comb it out ready for the tile---

Some times I'll use a 6" drywall taping knife (If it doesn't mean another trip to the truck to get it)
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Old 01-04-2012, 06:28 PM   #12
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Cement board at tub lip


I've just spent an hour or so looking for this exact answer and you guys were the most helpful by far. Also a novice, so wish me luck! Thanks again.
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Old 01-04-2012, 06:52 PM   #13
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Thanks testarosa---The search engine here is stink-o.

If you have questions consider opening a new thread of your own--There are plenty of folks here with tub and shower experience--Mike---
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Old 02-22-2013, 10:02 AM   #14
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Cement board at tub lip


This is so helpful!!!

Can I ask a dumb question concerning "filling" that 1/8" gap?

It was mentioned to use "tile mesh" (for the hydroban or thinsit to cling to).

What is that? I know tile mesh holds tile together as in the case of mosaic tiles, normally, but can it be purchased separately?

Sounds even more like a REALLY dumb question after typing.
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Old 02-22-2013, 10:56 AM   #15
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Cement board at tub lip


I have been a professional roofing and waterproofing consultant since 1986, and it is amazing to me how many products, and methods have been developed that make people think they can ignore the basic facts of waterproofing. They are as follows:

1. Always give the water a way to exit the system. If you do not, it will find its own way.

2. Always shingle materials to drain, even if they are considered water proof.

3. Never depend on sealant or mastic to prevent leaks. Water is the universal solvent, and no sealant or mastic lasts forever.

Thinset = Mastic
Sealant- Wears out.

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