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Unread 01-08-2003, 02:46 PM   #1
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tiling over plaster

I'm a new weekend warrior, and am considering a bathroom project. I'd like to add a shower to an old tub, but the walls of my 1920's home are plaster. Someone in another forum suggested creating a bed of mastic over the existing plaster to seal it from moisture. Then, tile over the mastic bed using more mastic as the tile adhesive. Is this an adequate solution. Or, can cement backer board be hung on plaster? I'm trying to avoid having to rip out plaster walls. Thanks.

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Unread 01-08-2003, 03:29 PM   #2
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Bob, I think you need to go to the liberry or read more of these threads. Mastics and showers DON'T go together. I think you could use 1/4" hardibacker board over the plaster but wait until the professional tilesetters get here for their authoritative statements.

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Unread 01-08-2003, 04:09 PM   #3
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Plaster is neither flat nor plumb. Indeed that is one the characteristics that people like to see, the wavey walls, like bubbles in glass, it shows handcrafted work. Unless your plaster is very flat, you will not be able to tile over it, and may not even be able to lay a CBU on it.

If you decide it is flat enough (use a 6 foot straight edge), then I would locate the studs and make appropriate marks on the ceiling above them, apply a good thinset, some backerboard, and nail away with some fairly long (inch and three quarters) roofing nails. I would waterproof the CBU with a trowel on waterproofing then tile away.

I would rip out the plaster, however. You will have some thickness issues at the edge, and may have to lay some quarter round or mud edges to make the transition back to the plaster. The plaster is usually about a half inch thick, so a simply bull nose works for the transition. The CBU panels will be flatter, too.
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Unread 01-08-2003, 07:28 PM   #4
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Hi Bob, Welcome.

I wouldn't rip out the plaster. I would figure a way to get 1/2 inch backer board attached to it in a somewhat straight and true manner, and then I would tile it and use mud caps (A4200 or A4300) on the edge. This is only a tub surround, right? I would hire someone to mud it before I would tear it out. Or you mud it yourself.
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