Cementboard and Silicone?

rolls831 · 01-24-2009, 01:26 PM

I recently installed hardibacker board in a walk in shower. Leaving 1/8" gap between, then filled with waterproof silicone. I plan to use mesh and thinset over the seems also. Is this overkill and is this a good process? Thanks

angus242 · 01-24-2009, 02:30 PM

Quote:

Originally Posted by rolls831

Leaving 1/8" gap between, then filled with waterproof silicone.

Gap where?

rolls831 · 01-24-2009, 07:28 PM

Hi Angus242. Thanks for the reply. The gaps are between the sheets of backerboard where they meet, also where the board meets the shower pan. This is a full walk in shower 33x60.

Tom Struble · 01-24-2009, 10:50 PM

silicone is not the best sealant for porous materials better off with a urethane

**Termite** · 01-24-2009, 11:23 PM

If it isn't too late I'd remove the silicone and properly fill/pack the joint with thinset and of course mesh tape the seam. Honestly, there should not be a gap at all.

angus242 · 01-25-2009, 12:10 AM

The even plane seams should be addressed with alkali-resistant tape and thinset, no gaps. The gap between the tile and shower pan will be caulked.
You should waterproof before tiling.

rolls831 · 01-25-2009, 02:15 PM

I'm including a photo. The gaps are 1/8" as you can see they are filled with 100% silicone. I will apply mesh then thinset. after drying and smoothing, I plan to coat with RedGuard. I really don"t want to remove the silicone unless an expert says this will lead to a disaster.

angus242 · 01-25-2009, 04:25 PM

I don't understand why you chose to leave gaps filled with silicone.

ANSI standard A108.11 states to use alkali-resistant tape over the seams and then fill with thinset. This would be true for all seams except to the floor, shower pan or tub deck.

Hardibacker installation instructions say to follow ANSI A108.11. It also states to tape and fill seams as above.

TCNA method W244C-07 also says to tape and fill with thinset.

None of the above methods say to have vertical gaps.

Furthermore, thinset will not adhere to silicone.

You've decided to use your own installation method. I don't see disastrous results but you've strayed from tested building procedures. The "overkill" isn't taping and using thinset on the seams, it was the use of silicone in all gaps.

01-24-2009, 01:26 PM	#1
rolls831 Member Join Date: Jul 2008 Posts: 31	Cementboard and Silicone? I recently installed hardibacker board in a walk in shower. Leaving 1/8" gap between, then filled with waterproof silicone. I plan to use mesh and thinset over the seems also. Is this overkill and is this a good process? Thanks

01-24-2009, 07:28 PM	#3
rolls831 Member Join Date: Jul 2008 Posts: 31	Cementboard and Silicone? Hi Angus242. Thanks for the reply. The gaps are between the sheets of backerboard where they meet, also where the board meets the shower pan. This is a full walk in shower 33x60.

01-24-2009, 10:50 PM	#4
Tom Struble Member Join Date: Dec 2008 Location: west milford n.j. Posts: 2,692	Cementboard and Silicone? silicone is not the best sealant for porous materials better off with a urethane

01-24-2009, 11:23 PM	#5
Termite Moderator Join Date: Apr 2008 Posts: 6,520	Cementboard and Silicone? If it isn't too late I'd remove the silicone and properly fill/pack the joint with thinset and of course mesh tape the seam. Honestly, there should not be a gap at all.

01-25-2009, 12:10 AM	#6
angus242 K&B Remodeler/Tile Guy Join Date: Apr 2008 Location: Illinois Posts: 887	Cementboard and Silicone? The even plane seams should be addressed with alkali-resistant tape and thinset, no gaps. The gap between the tile and shower pan will be caulked. You should waterproof before tiling. __________________ Angus To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Cementboard and Silicone?