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Bathroom Wall tiles and backer board

After making a decision to repair the grout that has loosened in one of my bathrooms using my new dremel multimax grout remover, I discovered that whoever did the tile/tub installation in the first place made a grave error of not making sure the cement backer board went ALL the way to the top of the bath!!! There is an inch gap between the top of the tub to the cement board! I was flabber gasted that something like this would have even passed inspection when the house was originally built back in 1991, but that's another story!! Luckily I could see no trace of water damage behind the tiles or behind the cement board. So it looks like many of the tiles will need to come off. My question is, how far up should I go?? Also, do I replace the backer board the entire span of the tiles or  just up to a certain level? Or will it make more sense to demo/.remove all tiles from all walls and re-do the cement board?? 


Is Hardibacker better to use than cement board with wire? I know Hardibacker cuts and installs like drywall, which would make it easier, but which backerboard is superior?


Also, for a vapor barrier, would the PVC sealer (pink when wet, and red when dry) work as a vapor barrier, and also serve as a way to have some give so tiles don't crack over time?



Andrew in MN

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Posted 2010-12-27T21:02:03+0000  by amoxom amoxom

Hey Andrew

Welcome to the community!


There are few different installation techniques when it comes to backer board installation around the tub and one of them is to place backerboard on top the bathtub flange ,fill the difference with thinset and bring the tile down to the rim of the tub. The main reason for this type of installation is to avoid bowing of the backerboard in other words if you bring a cement board down and overlap a lip of the tub you will end up with  some slight bowing, slight but noticeable. Some pros will say that this is acceptable some will say it’s not, in my opinion there is a better way of doing this. But before I get to the “better way” I will briefly explain disadvantages of the above installation. The main disadvantage is that if you rest a backerboard on top of the flange you will not have a suitable substrate for thinset to grab to and it will result in a problem that you have right now, also in addition there should be a 1/4 capillary attraction break in between a backerboard and top of the tub (not flange).In other words thinset fill that you discovered will eventually fail because it does not adhere well to enamel.


Now enough about that lets talk about the “better way”.

The reason nowadays people use a cement board in the bathrooms it is because cement board will not deteriorate from bathroom moisture and it will give out water faster. Vapor barrier or vapor diffusion retarder is there to stop the  moisture from bathroom  to pass  thru grout and cement board to the wall cavity; in hot climates you would need a VB on the exterior and on the interior wall while in cold climates just on the interior. Now there is something else to in between these two that almost always get’s missed an air gap. Any cement board that is installed right over a vapor barrier will have a slower drying time because of moisture that is trapped in between vapor barrier and cement board  that’s why is essential to have an air gap in between cement board and vapor barrier to allow faster drying time. Faster drying time will result in overall longer tile life and dryer bathroom, better bathroom.


And the easiest way to create an air gap and take of your problem is to install in following order;

1.       Unfaced insulation

2.       Vapor barrier

3.       ¼”Furring strips

4.       Backerboard on top of the tub with a ¼” capillary gap



I have also attached a good read from my fellow associate HD116 click here that explains few different types of vapor barrier and insulation that you can refer to as well.


Hope that helps and good luck with your project.






Posted 2010-12-28T15:41:41+0000  by George_HD_CHI
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