# Cement board at tub lip



## oh'mike (Sep 18, 2009)

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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## Homerepairguy (Aug 1, 2010)

oh'mike said:


> 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.



> 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".



> 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? 



> 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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## oh'mike (Sep 18, 2009)

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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## Homerepairguy (Aug 1, 2010)

oh'mike said:


> 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.
> 
> ...


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


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## oh'mike (Sep 18, 2009)

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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## Homerepairguy (Aug 1, 2010)

oh'mike said:


> 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.
> 
> ...


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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## oh'mike (Sep 18, 2009)

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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## Homerepairguy (Aug 1, 2010)

oh'mike said:


> 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. :thumbsup:
HRG


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## Roxerroneous (Oct 16, 2011)

oh'mike said:


> 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.
> 
> ...


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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## oh'mike (Sep 18, 2009)

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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## Testarossa214 (Jan 4, 2012)

*Thank you!*

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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## oh'mike (Sep 18, 2009)

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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## mplut (Feb 22, 2013)

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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## jagans (Oct 21, 2012)

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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## paintdrying (Jul 13, 2012)

Could you fill the space between the tile and tub with chalk only? Best way to cut half inch cement board? Can cement board be put up over existing drywall /plaster? I also have to ask this one, I was watching a home depot video where the guy started tiling at the top and went down, he taped each piece together as he went. Is that how a pro would do it?


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## mplut (Feb 22, 2013)

jagans said:


> 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.


I think that is what we are all desperate to do - find the best way to build and let the water drain....

That gap above the tub is so worriesome...hence the questions


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## oh'mike (Sep 18, 2009)

paintdrying said:


> Could you fill the space between the tile and tub with chalk only? Best way to cut half inch cement board? Can cement board be put up over existing drywall /plaster? I also have to ask this one, I was watching a home depot video where the guy started tiling at the top and went down, he taped each piece together as he went. Is that how a pro would do it?


I'm not sure if the thinset will bond to caulk----

Tilers mesh looks like drywall mesh tape---except it is alkali resistant--so it won't dissolve when embedded in thinset---

1/2 inch cement board ,like Durrock, can be scored and snapped like drywall--curved cuts can be made with a jig saw and a carbide blade--

A diamond blade in an angle grinder will work well for the zig zag cuts--
Or a hand held diamond circular saw--with a wet sponge against the blade---

Only on You Tube will any one start tiling at the top of a wall----

Frequently a wood ledger board is screwed to the three walls--leaving out the first row of tiles----then tile upwards ,using the ledger to keep the tiles from slipping---

After the tiles are set---the ledger is removed--screw holes waterproofed---then the bottom row is set----


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## joes plumbing (Jan 27, 2013)

Yes good to go with what you want to do good luck


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