tanking cement backer boards?

[ragsta]

Hi all, Ive just been sealing and taping cement backer boards, the marmox type in my shower area(waterproof core)1 coat then the tape and a coat over the top. 1 more once its dried. I've done this on all joints including the edges of the tileable wet room tray, about 15m worth.

Question is, once water gets through to the cement backer top layer won't it slowly absorb under the sealed and taped joints by moving in the cement layer? Or am I worrying too much. I could paint the membrane all over the tray and some way up the wall?

I will be tiling with 60x30 porcelain(24kg sqm) so I'm concerned about the tile weight limit of a tanked backer board.

What do you think, thanks

 

[tpt]

you are worrying too much. depending on the brand you can prime with SBR to make them fully waterproof, but its often not needed.

 

[AdamCH]

I think with Marmox you use their cartridge sealer between the boards to seal them. Probably not necessary but would take care of this scenario you present.

 

[ragsta]

thanks fellas. They are by prowarm. It isn't a power shower so that's a plus i guess. From all the instructions i've seen with these waterproof core boards only the joints need sealing/taping. Your right i'm probably worrying too much.

The cartridge sealer would work but not on corners i suspect because the cement surface of one board would still poke through to the other side. Then if any cement adhesive is in contact with this area or any flat joints without a sealant surely it would take up the moisture and then its into the building fabric.

Anyway i guess this tiny amount of water is not a problem. I hate stressing. i just needed confirmation. thanks guys.