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Due to an offset between the plumbing and the shower drain I need to float the wall on the short side of the shower base with like 3/4-1/2" so I am using top to bottom shims. I am not sure if the screws that I have (1-1/4" Durock screws) fit the purpose.

Can I still use them? (They will be 1/2" in cement board, 3/8" in the shim and 3/8" in the stud.)

Just to play safe I bought 1-5/8" screws that are from a different manufacturer. I'm not sure if I can still use them with USG Durock cement board.

It seems that for both it is essential to have a larger head, coarse thread, resistant to corrosion and sharp enough to penetrate the cement board which is stronger than the drywall.

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  • If you're really concerned about the diameter of the screw (from a comment below), why not return the 1-5/8" screws and buy the brand you're comfortable with in the length you need? Also, unless you've already opened/used some of the shorter ones, you could probably return those, as well.
    – FreeMan
    Sep 1, 2021 at 14:32
  • I don't see any mention of screw diameter.
    – isherwood
    Sep 1, 2021 at 14:49
  • FYI, you could also just use coated deck screws in pairs if you wanted even more penetration. That's how drywall was done using nails in the old days. It's not rocket surgery. :)
    – isherwood
    Sep 1, 2021 at 14:50
  • I did not open any of the two boxes. The problem seems to be that they are the only two options available in HomeDepot Canada in Toronto
    – MiniMe
    Sep 1, 2021 at 14:50
  • I thought the head shape and size is essential in this case. Seeing how fragile the cement board is I am going to have to test how it behaves with these screws, my first impression without testing is that they might crush the cement board, I might need to adjust the drill to tighten to a specific pressure only The deck screws might have a too small head
    – MiniMe
    Sep 1, 2021 at 14:52

1 Answer 1

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The 1-5/8 cement board screws are much better for this purpose, as they'll go through your 3/8" shims and still have 3/4" in the stud. Even if your shims are fastened securely to the studs it's much better to have the cement board securely fastened to the studs with its own fasteners and not relying on the shim-to-stud fastener.

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  • what I am not sure is if the two types of screws are compatible
    – MiniMe
    Sep 1, 2021 at 14:16
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    Any coated cement board screw is fine.
    – isherwood
    Sep 1, 2021 at 14:24
  • these 1-5/8" screws are thicker ..should I predrill in place (both the cement board and the shim) before I put the screws in ? I am afraid that they might split the shims
    – MiniMe
    Sep 1, 2021 at 14:31
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    @MiniMe - predrilling... that seems like another question.
    – DMoore
    Sep 1, 2021 at 14:35
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    You can pre-drill but keep in mind cement board eats drill bits for breakfast, they will dull very quickly. Cement backer board screws are designed to be self-drilling. If your shims are prone to splitting it's even more important to depend on the stud and not the shim to carry the weight of the cement board. Sep 1, 2021 at 14:37

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