# Cement board overhanging bathtub lip?



## onmywayup (Aug 18, 2012)

I don't normally do a lot of tile, but am re-doing a shower as part of a much larger project for a family member who doesn't mind if I practice tiling there. I have a quick question:

I've got half the cement board up around the shower walls and I'm having a bit of a debate with myself about one particular point. Does the cement board itself have to extend out over the ridge along the top of the bathtub? As I have it now, the inner surface of the cement board is basically flush with the ridge on the tub, then the tiles would stick down and overlap the ridge (once you figure in for the thickness of the thinset). 

Will that be sufficient? Or does that cement board ALSO need to extend down over the lip and nearly touch the top of the tub surface itself?


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## 4 seasons (Jan 4, 2010)

I like to have them both on top of the flange.


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## MAULEMALL (May 16, 2010)

http://www.mustee.com/product-lines/shower-floors/downloads/pdf/SI_190.pdf


go to page 6 figure C do it like that and you are good to go.


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## overanalyze (Dec 28, 2010)

If you want the cement board to overhang the lip of the flange you will need to fur out the studs so that the cement board can lay flat. Otherwise set the cement board on top of the lip and use thinset and tape to feather the joint. What are you using for your waterproofing?


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## onmywayup (Aug 18, 2012)

overanalyze said:


> If you want the cement board to overhang the lip of the flange you will need to fur out the studs so that the cement board can lay flat. Otherwise set the cement board on top of the lip and use thinset and tape to feather the joint. What are you using for your waterproofing?


For waterproofing, we are applying some sort of thick liquid roll-on stuff that my customer found. I've tiled a couple other showers, and this was the first time I'd heard about waterproofing the cement board. I wish I could recall the brand of product, but it was definitely labeled for cement board use. 

Kindof a thick blue goop......


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## ohiohomedoctor (Dec 26, 2010)

Aqua defense.


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## overanalyze (Dec 28, 2010)

onmywayup said:


> For waterproofing, we are applying some sort of thick liquid roll-on stuff that my customer found. I've tiled a couple other showers, and this was the first time I'd heard about waterproofing the cement board. I wish I could recall the brand of product, but it was definitely labeled for cement board use.
> 
> Kindof a thick blue goop......


The doc is right..prob aqua defense by Mapei. That's good stuff. Make sure all your joints and corners are taped and mudded with thinset. Then apply two heavy coats letting it dry in between coats. Use a good modified thinset to set the tiles. Are you clients paying you to experiment on their shower? Can have a lot of problems if you are unsure of how things need detailed. We can only offer so much help...


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## ohiohomedoctor (Dec 26, 2010)

You guys built a Nick you can walk this guy through a shower install..


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## overanalyze (Dec 28, 2010)

ohiohomedoctor said:


> You guys built a Nick you can walk this guy through a shower install..


Not sure why..was feeling especially helpful this evening..lol!


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## ohiohomedoctor (Dec 26, 2010)

Your always pretty helpful


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## onmywayup (Aug 18, 2012)

overanalyze said:


> The doc is right..prob aqua defense by Mapei. That's good stuff. Make sure all your joints and corners are taped and mudded with thinset. Then apply two heavy coats letting it dry in between coats. Use a good modified thinset to set the tiles. Are you clients paying you to experiment on their shower? Can have a lot of problems if you are unsure of how things need detailed. We can only offer so much help...


Your concern is appreciated. You all are a huge help on these forums, but at the end of the day, I have to get out there and start _doing_ the work, making some mistakes, then paying (in time and money) to fix 'em. 

When my second child was born last year, there was a new anesthesiologist resident who came in to do the epidural for my wife. He stabbed at her back like Ray Charles was going at it, before the big doc stepped in and took over. Mistakes must be made in order to learn, but I really do appreciate you all helping me skip over the obvious ones. 

I've got a pretty good grasp on this and the last couple I did turned out fairly well, but I know now I missed a couple of details on those first ones that might burn me down the road.


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## CHRenewal (Aug 12, 2012)

MAULEMALL said:


> http://www.mustee.com/product-lines/shower-floors/downloads/pdf/SI_190.pdf
> 
> 
> go to page 6 figure C do it like that and you are good to go.


+ 1......This is it


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## Worm Drive (May 2, 2007)

MAULEMALL said:


> http://www.mustee.com/product-lines/shower-floors/downloads/pdf/SI_190.pdf
> 
> 
> go to page 6 figure C do it like that and you are good to go.


So the caulk is the only thing that water proofs that joint? Seems like there would be a better way.


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## onmywayup (Aug 18, 2012)

Worm Drive said:


> So the caulk is the only thing that water proofs that joint? Seems like there would be a better way.


Well in this particular case, we ended up waterproofing the surface of the cement board itself with a roll-on product, then made sure that the cement board wasn't sitting on the tub itself (to avoid wicking). Seems like enough to me with the caulk. 

Pro tile guys? Your input?


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## [email protected] (Aug 9, 2011)

I always use color matched silicone around the tub and down the corners. Works great.


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## The Coastal Craftsman (Jun 29, 2009)

Mapei make a color Matched sanded caulk, unsanded caulk and silicon.


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## stonetile71 (Jan 26, 2012)

only one way to find out. Blast it with the hand-held and chexk fo leaks.


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## MAULEMALL (May 16, 2010)

Worm Drive said:


> So the caulk is the only thing that water proofs that joint? Seems like there would be a better way.


If you had gone a little further to figure D you would see the _OPTIONAL _seal gasket ... But silicone is more than acceptable and complies to the warranty..


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## Ethos (Feb 21, 2012)

I bring my Denshield down to the top of the lip (because furring out the studs means my tile would pop out too, and rabbeting the sheet material is a PITA) and then using a putty knife, filling that gap and smoothing it out with Wedi sealant. 100% silicone will work just fine as well, or any other flexible, waterproof sealant.

People still using CBU makes me sad. It's a product that requires that you seal the entire surface with an expensive waterproofing membrane or liquid membrane. It's hard to cut cleanly. It's not waterproof. It requires special screws to install properly. I've been harping on so many threads that I will gladly make a video of a much easier method on my next tile shower coming up in about 3 weeks: Denshield + Wedi sealant is your friend.

CBU had no pros to this comparison.


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## onmywayup (Aug 18, 2012)

Ethos said:


> CBU had no pros to this comparison.


Now that's an interesting post. I haven't heard of Dennshield before. I just did a quick search and the stuff looks interesting. 

Can it be purchased at HD/Lowes? All I've ever seen there is HardiBacker and Cement Board.

How does it compare to HardiBacker and what about price?


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## Inner10 (Mar 12, 2009)

onmywayup said:


> Now that's an interesting post. I haven't heard of Dennshield before. I just did a quick search and the stuff looks interesting.
> 
> Can it be purchased at HD/Lowes? All I've ever seen there is HardiBacker and Cement Board.
> 
> How does it compare to HardiBacker and what about price?


Depends on your location in my city some carry 4x8 sheets, some 3x5, and some both. Runs about the same price maybe a couple bucks more a sheet.


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## Ethos (Feb 21, 2012)

onmywayup said:


> Now that's an interesting post. I haven't heard of Dennshield before. I just did a quick search and the stuff looks interesting.
> 
> Can it be purchased at HD/Lowes? All I've ever seen there is HardiBacker and Cement Board.
> 
> How does it compare to HardiBacker and what about price?


You typically need to find a tile supplier that carries it, however every major city should have at least one. My supplier can get me a 1/2"x5'x4' sheet of Denshield for about $15, and a 1/4"x4'x4' runs me about $10. As for Wedi adhesive, you need to find a Wedi dealer, or you can use something like Sikaflex 221 (thinset will stick to these adhesives, but not at all to silicone). Simply fill your seams and screw holes, a process that takes about 30 minutes for a typical shower, and you're good to go. The stuff dries well enough to tile over in about 30 minutes to an hour.


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