Ok to reuse mortar vanity substrate? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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03-08-2005, 01:45 PM
I pryed up all the 4.5 builders white tile. There is a 1.5" mortar bed underneath that seems to be in solid shape. The back splash substrate is CBU, and also looks to be in good shape. Overall, it's level, square, and looks to be ready for tile.

Ok so now for reality - I was pretty careful, but I was using a hammer and prybar. I tapped the prybar under the corners of the tile and pryed them up. Most popped up fairly easily. The deck was set first, and the backsplash CBU was set on top, so there was some movement between the vanity deck and CBU when prying them out.

I tapped across the surface with a mallet looking for anything loose. nothing.
I can only see one hairline fissure (leading from the sink cutout, to the backsplash) but I have to pull up very hard to get the crack to separate at all. Still, seems to be very solid.

So... how should I test to make sure it's good to go? Would anyone consider ripping it out just for the hell of it? Looks like 3/4" OSB underneath.


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03-08-2005, 02:36 PM
Because of the crack I'd cover the mud with an antifracture membrane. Redgard will work.

You caulk the joint between the countertop and the backsplash, so that little bit of movement is OK.

03-08-2005, 03:11 PM
Thanks. I will redguard. I was going to tape that joint with fiberglass tape and thinset. SHould I do that? Caulk, or both?

03-08-2005, 04:10 PM
Caulk the top to backsplash joint. No tape and thinset.

03-08-2005, 11:22 PM
Now I'm really confused. I submitted a similar question for my tubdeck to backsplash CBU joint here (http://johnbridge.com/vbulletin/showthread.php?t=19917&highlight=CBU+joints) and got a different answer. (response #3)

So I filled and taped all the inside corners, and that area is now finished.

Now I'm doing the vanity with backsplash...

I guess I don't understand... do you ONLY tape/thinset joints when they are on the same plane?


03-08-2005, 11:51 PM
Hi Michael.

You did it right, thinset and tape in the corners. :)

I don't see a conflict with response #3 (from ChasR) in your other thread. The context of that discussion was: thinset, silicone, or foam in the corners? Answer is thinset. ChasR didn't carry the response to the next step, tape; or the next step after that, tile.

You're OK. :nod:

03-09-2005, 12:20 AM
Thanks Mike.

Update since demo... The vanity deck is in great shape, but they didn't screw the Hardi down for the splash... they glued it to the drywall!!!

I popped it off with one tap... wish I know that - demo would have been really easy ;).

Because they had CBU on top of the drywall, they used cove edging to fill the gap... which i guess is standard (if you've got a mud backsplash). I'm using stone and prefer to have the stone right up against the "wall". So I pulled out 10" of drywall around the vanity and screwed up 1/2" hardi instead. Tomorrow I'll tape and mud it.

Thanks for your help!