How do I backsplash over wavy drywall?

For minor differences in the wall you can use the thinset to create a smooth finish. Place the thinset on the wall then butter the back of the tiles with thinset and set in place.

It would be much easier to level it out with the drywall spackle.

I had the same problem on my living room wall. I used drywall mud. If the wall is really wavy, put the mud on in layers, letting it completely dry before adding next layer. Use a level or straight edge to determine when the wall is even.

The quick, easy treatment is to buy a sheet or two of 1/4" backer board and screw it into the studs. This stiff board is made for tile applications. You will need to tape and mud any joints. Check YouTube for assistance.

Drywall mud is the best way to level it out. After you mud the wall and install the tiles, grout everwhere except the bottom. Run a bead of caulk along the bottom.

Jeremy,

if you replace the drywall with cement backer board remember that your wall studs are probably not completely flat (might be bowed or crowned) causing the waviness. You will need to fur/shim the studs in order to get a flat surface for whatever material you use. Check out this youtube.

https://www.youtube.com/watch?v=e2yYse0cd_E

What kind of backsplash are you installing and what's the biggest gap behind the counter?

Thank you for all y’all input, Seth that’s my biggest worry about replacing the drywall is working on the studs. Frank, the biggest gap is only 3/16 but they also cut the drywall out to fit the countertop under the drywall about 3/16-1/4”

You should be okay filling dips with thinset if only 3/16" deep. More than that and you run the risk of the tile popping. A 12x12 is pretty heavy and a deep layer of thinset may not hold that much weight. You might be better off filling the dips with joint compound first.

I had the same problem and did not want to mess with the drywall. I used small tiles 1 x 1 marble, on sheets. The "waves" were not noticeable at all when it was finished.