caulk between backerboard and shower pan

[lucygirl1992]

Hi;

I'm laying tile in a second floor bathroom. There is an OSB sub- floor. I put 1/4 inch backer board (Hardi) down on the sub-floor and used thinset and screws to attach it down. I haven't started tiling yet.

Prior to this there was just carpet over the OSB sub-floor, and we had a small mold issue at the shower; water drips when we open the shower door and it soaked through the carpet and got the OSB wet and there was some mold growth on the carpet there and the sub-floor.

I cleaned up the mold very thoroughly before laying down the backer. There is an 1/8 inch gap between the shower pan edge and the backer board, and I'm worried that moisture will get in there as it did before.

I read somewhere, but I can't find it again, that I can/should put a bead of silicone between the backer board and the shower pan to seal off the possibility of water getting in there. Then, I'll have tile over that, with another caulk bead between the tile and the shower pan.

Does this make sense to do? If so, what kind of caulk should I use between the backer board and the shower pan? I think I would use GE Silicone II.

Comments appreciated.

[Mikepier]

It would not hurt. The GE stuff would be fine. But if you tile and grout correctly, you should have no water problems.

[John Grabowski]

Do it. Not sure what caulk to recommend, but every little bit of protection helps to prevent water from traveling.

[EXT]

You could use Schluter KERDI to seal the backerboard and the joint between it and the shower base. An 1/8" gap could pose a tile laying problem when trying to fit the tiles against the base, doesn't the shower base have a lip all around that fits behind the tiles to aid in waterproofing the joint?

[Red Green]

Mikepier wrote in news:1fdef5db-d47a-4819-9b52- [e-mail]:

Even with brand new tubes, before actually caulking squeeze some of the silicone on scrap. In 30 min it should slightly skin. If it doesn't, don't use that tube. It will not dry/fully dry. GE silicones are notorious for it. I got burnt once.

Well, shit happens ya know.

[Joe]

Many posts in this NG relate problems with GE silicone II. Short shelf life, failure to cure completely, etc. Personally I can confirm the problems. The original silicone formulations are still the best. I've used tubes that have been around the shop for some years with no difficulty at all. But you may want to consider another high performance or specialized sealant, because anything the silicone touches will inhibit bonding of tiles in that area. Polyurethane door and window sealants are possibilities. Choose wisely and good luck.

Joe

[DanG]

I would not use silicone. Any of the good polyurethanes would work well. NP1 is my favorite.

[lucygirl1992]

Thanks very much for all of the responses. For the folks who recommended polyurethanes over the silicone, why is this? Any particular reason?

Thanks.

[lucygirl1992]

The 1/8 inch gap was what was recommended on the installation instructions for the backer board. I guess I'm just figuring since that piece of tile will not be loaded it will be OK to overhang the edge of the backer?

The shower base doesn't have a lip, it just goes straight down and sits directly on the subfloor without any kind of flange or lip.

[Joe]