How to patch wallboard behind shower tile

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Old 02-23-16, 09:56 AM
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How to patch wallboard behind shower tile

I just replacing a leaky tub/shower valve. As it turned out, I wound up replacing all the galvanized pipe with Type L copper. Needless to say, I got a crash course in working with copper pipe, soldering, etc. Despite never having done any of this type of work before, I'm extremely proud to say I had no leaks whatsoever upon completion of that phase. Thank God for forums like this one and the extremely informative videos on YouTube, in particular "TheOldKid888" (Al aka Old Plumber).

Anyway, a strip of the wallboard to which the ceramic tile is glued has been damaged and needs to be patched (see photo). It appears to be made of a form of concrete similar in construction to sheet rock. I don't think there are any remaining pieces of that material sine my late father-in-law remodeled the bathroom in the mid-70s. And there's not enough damage to justify buying an entire sheet of material.

I was thinking using some type of mesh with a patching material but I'm not sure what's the best way to approach this repair. I'd appreciate any suggestions/advice on how to go about it.

Thanks!

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Old 02-23-16, 03:12 PM
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Sad to say it looks like drywall, which is not a good backer for tile. You have a woefully weak area under your mixing valve (Oh, congratulations on the installation) and any repair will not be an optimal one. One way that will give a little more life to it would be to embed mesh tape, or even fiberglas mat and coat it with spackling compound (which is harder than sheetrock compound). Once it dries it may help with stability of the wall.

Others will chime in on this, so give time for other ideas as well.
 
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Old 02-23-16, 03:17 PM
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Larry would you be referring to a setting compound like Durabond? it's not water soluble.
 
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Old 02-23-16, 03:27 PM
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I think I might try this. Tape the pipe and fittings with duct tape. This is so nothing bonds to them.
Then mix up some concrete patching material get some by Quickcrete, I forget what type exactly but it comes in a yellow plastic pail and sets quickly. While you are getting that get some of their bonding agent, not the fortifier that you mix into the mortar but the stuff that smells like Elmer's Glue and paint the tile, the edges of the drywall of plaster or cement plaster base or whatever you have there and the back side of what we see in the picture, then fill in the void but don't fill it extra full. Let this set. Then get some 1/4" hail screen or expanded metal lath or woven stucco wire or chicken wire or something like that. You might be able to scrounge a scrap or two for this. You can buy a small piece of screen if you must,
You are wanting to reinforce another coat of mortar that you will apply and then embed the wire or lath or whatever in and add yet more mud. Don't let any steel contact the copper.
This sounds complicated but it really is not. It should only take a few minutes longer to do all of this than the set time of your mortar, whatever that is. It does not have to be pretty you just want something strong which will not give when you turn around and bump the tile with your elbow.

I suggest cement because it is harder stronger and more water resistant than anything else. I see that while I was posting this someone asked about Durabond. I think that is a poor second choice but if this ever needs done again would be easier to take out without ruining the tile.
 
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Old 02-23-16, 03:34 PM
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One more thing Keep what ever you do away from the hole where the valve is. You might want to get to that from the other side of the wall sometime and you don't want it full of mud.
Also maybe to be on the safe side have someone hold against the tile on the other side so you don't push it off of the wall when you do the work.
What you want to do is stick mortar to the tile and surrounding then reinforce another coat that is larger and bonded to the back side of the sheetRock in as large an area as you can work on to tie all this together.
 
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Old 02-24-16, 09:43 PM
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Thanks, guys! The wallboard is constructed almost exactly the same way limestone sheetrock but the material in this is not chalky stuff that falls apart pretty easily. This material, when it breaks down, reminds me of soft lava rock I saw in some museum when I was a kid. In pristine condition it's almost like pumice stone, like my mom used on her feet when I was a little kid. But once it gets wet it just crumbles int0 peanut-sized chunks with or without the paper backing.

Anyway, Lightcoat, you described almost perfectly what I was thinking about doing! Sp thanks! I'll be starting back on it this weekend!

Thanks soooooooo much! I'll be getting back on this tomorrow or Friday at the latest.
 
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Old 02-25-16, 05:55 AM
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I like tightcoat's idea of the cement and mesh. It's like you're making your own mortar bed after the fact and this will hold the tile well.
 
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