Prepping the backsplash for mosaic tile

[mtnbiker3000]

Just had a new quartz countertop put in, and the area above the sink and below the bar used to have subway tile. When the countertop guys pulled off the subway tile it jacked up the sheetrock behind it. I don't really care as I am going to put a mosaic backsplash up, but wondering the best way to prep the now very uneven surface for tile?

[mtnbiker3000]

Images =)

[cx]

Welcome, Brian.

Best approach to my thinking, provided there is enough overhang of that upper surface, would be to install strips of a 1/4" CBU to cover that splash and provide a much flatter surface.

Second choice would be to flatten the entire surface with some sort of cementitious patching compound.

While you can probably bond to what you've got there, it's not gonna work well with small mosaic tiles, which will try to follow the contours of that backing. A larger format tile might go over the whole thing with no real problem.

My opinion; worth price charged.

[mtnbiker3000]

Not a bad idea But, I would still need to fill some of the deeper voids with something even before the cement board, correct. Or else the CBU might bend or become uneven (following the profile of the damaged sheetrock)?

[Tool Guy - Kg]

Cement board will follow the contour. But it's still relatively stiff considering how short that span is. It's going to depend on exactly where you fasten the board in relation to the low spot. And I'd guess that the metal corner bead is causing quite a "high spot" in relation to the drywall surface?

How big are you mosaics?

[mtnbiker3000]

Seems to me like it's not so much the metal corner bead as it is the gouges out of the sheetrock that is causing the low spots (check image #3) Probably going to use the small glass tile mosaic. The tiles that are about 1" by 2" or so...

[cmilot6329]

How about filling in the low spots with sheetrock mud? I ran across something similar when I removed old baseboards. And the mud seemed to work good and adhere to the old drywall and paper.

[cx]

Gypsum-based fillers are less than optimal backing material for a thinset mortar application, Chris, but in that application I would not rule it out. I would recommend the setting-type drywall mud rather than the drying-type, but in either case the use of a drywall primer over the patch would be recommended by a lot folks.

I'd still favor some sort of cementitious patching material, though, and his situation does lend itself to easy flattening of the surface. Well, except for behind the faucet, of course, but shouldn't be too difficult to work around that. And I still think it might be easier to get a flat surface by starting with strips of CBU.

My opinion; worth price charged.

[mtnbiker3000]

I'm all for the CBU as that is how I have done tile in the past, so I am framiliar with that technique. I'm just not sure what to fill the voids with before the CBU goes up? What do you mean by cementitious patching material?

[Tool Guy - Kg]

Cementitious patching material is somewhat similar to drywall patching compound as it is mixed with water and spread with a wide putty knife. But it is cement-based, so it doesn’t turn to mush in the presence of moisture like drywall patching compound can. It is typically found in the flooring department of your favorite box store.

[mtnbiker3000]

Thanks for the tips!! I will post pics of the process and finished product...

[Davy]

I see no reason tape and bed mud wouldn't work. Get it as flat as you can and lightly sand it if it needs it. I'd let it set and paint a coat of Eco Prim grip on it. Custom's also has their own primer that works equally well.