I have a few points where the sheetrock is (already) not level between joints. About 1/16" or so. I will be adding hardy backer board which needs to span this joint.

I want to avoid (obviously) a non-level sub-surface for the hardy backer board and "float out" this section. What material should I use?

Since I am new to doing this, a specific type-of material name would be helpful, though I suppose specific "brand" names are OK as examples. Thanks.

Pictures attached, they show the gap a little bit. from over it

this shows the 1/16 level difference

  • Are you putting up hardy board over the green board so you can tile? I like to use Denshield. You use it in place of the green board ( same thickness as the 1/2 sheetrock so no uneven transition. You tile right on to it. – Alaska Man Dec 14 '17 at 2:45
  • I am putting HB over the green board, and because of where the tub sits down below (not shown) I have to. But the HB will be on both the finished and unfinished surfaces shown. I need to float it out. – Oliver Williams Dec 14 '17 at 2:49
  • You mean the mounting lip/flange of the tub is not behind the green board and so the the hardy backer will need cover the lip? Use thinset, the same as you are going use for the tile. – Alaska Man Dec 14 '17 at 3:00

You can use thinset mortar to float the gap. If the difference in surfaces is significant then you will need to float it out on the low side quite a bit.

It does not need to be to pretty but it should be relatively smooth. Use fiberglass mesh tape made for hardy backer on the seams to add strength; make sure the screw heads are counter sunk properly.

For 1/6 inch I am not sure it is necessary.


While I've not done this on walls, when I did this on floors I had to apply thinset before using fasteners to hold the boards down. 1/4" square notch trowel IIRC. Check out the data in your backer board to see what they recommend.

If they don't recommend anything, I'd just use plain old drywall mud (not spackle)

  • I'm not repainting, this is a shower. I need a level surface to put the Hardy Backer board on. Drywall mud is not something I'd use here. – Oliver Williams Dec 14 '17 at 2:51
  • Read the edit. I initially misread it to mean that you needed to level the two walls. I've made this apply to putting backer board over the holes – Machavity Dec 14 '17 at 2:52

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