How To join backerboard with Drywall

Old 02-27-07, 10:02 AM
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How To join backerboard with Drywall

Hello and thanks for taking time to answer my question.

I'm looking to replace some basic ceramic tile aorund my whirlpool tub and shower. The whirlpool tub sits in corner with two 48" windows above. the existing tile around tub comes short about 10-12" from meeting bottom of window frame.

The shower tile stops short of 12" from ceiling. There is a common wall between shower and tub (painted drywall) and the wall to left of tub is common with vanity wall (drywall painted).

Although I hate to go down to the stubs, I'm unclear how to join up the backerboard with the drywall. Is it possible to carefully remove the tile and drywall to up under the window frame around the tub and square off at the edge of tub before meeting drywall, so I can only replace just this part with backerboard?

Do I need to extend to all common walls until I reach a corner?

If I have backerboard meeting up with drywall, do I use drywall compound and tape to seal joints?

in the inside/outside corners where the backerboard meets the drywall, do i need to install drywall metal corners to reinforce or just tape?


P.S. is it true you leave a 1/4 gap between backerboard on floor and wall for expansion or do you just do this where the tile meets tub? I'm assuming you fill this with caulking, but can the basebaord cover this when reinstalling?
Old 02-27-07, 03:10 PM
Join Date: Jan 2006
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I'm not sure I follow your whole bathroom layout, but I'll try to give you some answers.

You can cut out sections of drywall that will be tiled and replace them with cement backerboard. You need to make sure that where the cement board and drywall meet that you have a stud behind that joint to fasten both boards to. If you will be tiling over a joint where cement board and drywall meet, then use alkalai resistant mesh tape and thinset on the joint. If you will not be tiling over the joint, then mesh tape and drywall compound. Keep metal corners out of the mix. Water eventually gets to them and they rot out. You will only need mesh tape and thinset on inside corners.

Yes you need to leave a gap where the cement board meets the tub, walls etc. Also leave a gap between sheets, dont butt them. You can caulk around the cement board at the floor/wall joint but its not necessary. You must also maintain that same 1/4" gap with the tile and the walls. You need to leave room for movement. Base tile or moulding will cover the gap.

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