I recently used mesh tape on all cement board corners on a tub area I’m about to tile. I didn’t realize there was mesh tape specifically designed for cement board. I just used the regular stuff for drywall and got everything finished and ready for tile using my thin set. It looks good and feels sturdy, but am I going to have major long-term consequences with the tape itself breaking down? This is a tub area, not shower, and it’s not going to be highly used.

Do I need to chisel it all out and redo those corners with the alkali resistant mesh tape? Or am I probably good?

  • 1
    are you going to use brush-on waterproofing membrane behind the tiles? – Jasen Oct 7 '19 at 22:49
  • Yes going to roll Red Guard on – Martin Oct 8 '19 at 0:14

Long term consequences? Yes. The thinset mortar and the backerboard will release alkali when exposed to moisture and over time that will deteriorate the fiberglass resins in the tape. Major consequence? Meh... the tape is there to reinforce the corners and edges against minor shifting in the house structure so that it doesn't result in straining the mortar, leading to cracks and dislodging of the tiles. If it's a tub area, only the lower areas will likely see enough moisture contact to affect the alkali release, so then the rest of the tape in the corners is still going to aid in keeping it all together. And besides, you may not get a lot of shifting of the structure anyway. Not everyone even uses tape at all!

  • wouldn't he be ok if he put a moisture barrier over the cement board?? like Redgard? – JACK Oct 7 '19 at 22:44
  • That’s what I was hoping. Sorry I should’ve clarified in the initial post that I will be applying red guard – Martin Oct 8 '19 at 0:26

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