Backerboard waterproof question. [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


View Full Version : Backerboard waterproof question.

01-18-2013, 09:58 PM
About to install 1/2" Durock backerbaord in my shower before tiling. Should you silicone the seams before the mesh tape and Redguard? I thought about running a bead along each edge before placing the next piece of Durock in. . .to better seal behind the tape and Redguard or will the Redguard not stick as well that way? The silicone would only leave behind a very thin bead after running finger across seam to remove any excess silicone. Are you better off to go NO silicone and just thinset the seams letting the thinset fill any cracks and voids? Thoughts? Thanks in advance for any possible help.

Sponsored Links

01-18-2013, 10:36 PM
Hi Nick,

Trust the RedGrd. Nothing sticks to silicone. Backfill joint with modified mortar and tape with alkali resistant BB tape at seams. Then proceed with Regard after about a 12 hr cure of mortar on the seams.

Good luck with your project.

Tool Guy - Kg
01-18-2013, 10:38 PM
Welcome to the forum, Clint.

No, you definitely do not want to use silicone between the Durock sheets.

Your method also implies that you won't be taping the joints with alkali-resistant mesh tape and using thinset to mud the joint. You most definitely want to tape and mud the joint. After that's completely dry, apply your two coats of RedGard, making sure they're of the proper thickness. A gallon will cover 40 sq/ft with two coats at the proper thickness. If it goes further than that, you're applying it to thin.


01-18-2013, 10:59 PM
Just a personal opinion here but...

I wouldn't use a joint tape over durarock or backerboard unless you can get a perfect smooth joint. Without that you risk having a high spot at each joint. Get the sheets tight enough and RedGard or Aquadefense can cover the joint or to be sure use a little modified mortar first to fill the joint lines. If those joints are flexing you have a different problem that no mesh covering is going to fix.

Any reason you chose durarock? It's a brittle product and a lot harder to work with than backerboard. But most of all stay away densguard - that's nothing more than small sheets of drywall with a thick waterproof covering - which sounds nice until you start punching holes in it when you install it with screws or ringshank nails. (So you then have to seal every one of those screw/nail heads and you still have compromised the integrity of that covering.)

Silicone sounds like a great waterproofing thing but in reality look as bathrooms where the they used clear silicone and you will find almost without exception - mold water etc will still find a way under it and yet nothing sticks to the surface as others have said.

Just another opinion but I've seen a lot of messed up jobs and listened to a lot of installers complain about the messes they have had to clean up.

01-19-2013, 01:20 AM
So you're suggesting going against manufacturers instructions and skip mudding and taping the seams Scott? :suspect: Not the best advice. You can do whatever you like on your own installs Scott but when giving advice on this forum we like to stick with manufacturers specs.

Also RedGard "suggests" the use of fiberglass mesh on seams and changes of plane. Got the ok from tech support this past summer that mudding and taping the seams with the BB tape was suitable

01-19-2013, 06:39 AM
Thanks guys. I was just thinking about the flexibility of the silicone if there were to be any slight movement in the backerboard but you all gave me the answer I was expecting. I was planning on applying a thin bead of silicone and then taping and mudding the seam but the adhesion over the silicone was what I worried about. I will just stick to doing things the way you're supposed to. :crazy:Thanks again for your help.

01-19-2013, 10:23 AM
Welcome, Clint. :)

When all else fails, read and follow the manufacturer's installation instructions, eh?

Not sure why Scott is separating Durock from backerboard, since Durock is a Cementitious Backer Unit and the instructions call for filling and taping all the seams after installation using thinset mortar and alkali resistant mesh tape as Chad has pointed out above. You should do that. They do not call for the use of any silicone between sheets. You should not do that unless you're building a steam shower and then we'd need to talk about the corner joints.

My opinion; worth price charged.