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carrie brooklyn 04-21-2006 10:45 PM

Help! Bathtub trauma
I recently hired a handyman to put up backerboard around my bathtub (I plan on doing the tile myself). He used moisture-resistant cement board, but didn't put a plastic sheet underneath and used joint compound and white paper tape to bridge the gaps between cement boards.


How problematic is using joint compound instead of mortar and fiberglass tape? I want to make sure this is done right and that we don't have any more problems with moisture getting behind the tiles. When I go over the joints with mortar, should I sand away most or all of the joint compound first?

Is it worth removing the cement board and putting a plastic sheet behind it before I put up the tiles?

lxdollarsxl 04-21-2006 11:47 PM

As the backer board is water resistant you shouldnt need plastic behind this will help it breath and prevent any sweating. As for the seams they do make a compound and tape for the joints, drywall compound and tape is not correct. Just ask at DIY store and the will fix you up.:)

Bonus 04-22-2006 12:15 AM

I have to respectfully disagree, there should be vapour barrier behind the cbu. However, you can get a product called Redguard that you can paint on the cbu. Also, as lxdollarsxl says, the drywall compoud and tape is incorrect and will fail. Use a mesh tape made for the purpose and thinset mortar. It's best to do this as you tile, that way you don't wind up with a 'bump' to tile over. It sounds like you already know this, but don't use the pre-mixed mastic to apply the tile, use the real thing- thinset mortar. Happy tiling. :)

crecore 04-24-2006 07:50 AM

The tape wont hold up, but had he used the plastic behind there would have been no need to "tape" the joints. A mesh, as Bonus says, will bridge and keep things from shifting and you just tape as you thinset... anything more throws the wall flatness out the window and you will see this when you grout.

Removing that now would be a total mess and there's always a chance that you could damage the tub as well. I would check into that Redguard stuff. and in the future makes some awesome products... well worth the reading for the info if nothing else.


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