Installing hardibacker and had a quick question while cutting out the hole for the HVAC register. The toilet, as I understand it, gets caulked around the base. So no special water proofing is needed. However, the register, I'm not so sure. I also can't find mention of it elsewhere on the internet.

So my questions are as follows:

  • Do I need to do any special waterproofing for the air register on the floor?
  • Do I use the mesh tape and/or the red guard waterproofing around this area?

My main concern is water going under the sides of the register, then getting to the hardibacker that way, as the tile doesn't go down the side of the register.

Any help is appreciated. Thanks.


I'm assuming you are going to tile the bathroom. Are you concerned with just moisture or accidentally overflow from the tub. Either way overdoing waterproofing is never a bad idea. Use the mesh tape and the red guard to seal the edge around the register and for an added layer of protection you could put a bead of caulking​ to the underside of the vent cover before installing.

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