I recently tiled a shower over bath and have an issue with moisture creeping through the grout and creating a dark section (water absorption) on the durock wall board behind the see through glass wall tiles.
I have since sealed the grout several times and am now concerned that the moisture will cause mold between the tiles and the tar paper I lined the wood studs with. I'm hoping the moisture will eventually evaporate now that the grout is sealed. But should I be concerned about mold? If so what can I do about it?

Thanks
Adam

Grout sealers are designed to let moisture pass through, even when sealed. As long as you overlapped the flange with the roofing felt, you should have no worries... maybe...

What specifically did you use to set the glass tile? ;)


Oh, and maybe a moderator could move their post to "interior home improvement" where is belongs, or back to "construction" where it was because it has absolutely nothing to do with plumbing at all.

I don't know if I will agree with Bljack claim - but if sealer allows water to penetrate through - then: what's the purpose of the sealer ? Please, educate me...

If you want to reapply sealer, make sure shower is not in use for 1-2 weeks. Walls must be 100% dry. No compromise there. Reapply.

If you stop moisture from penetrating, let remaining moisture to dry. Run fan against the wet spot until wall is dry. Do not use heaters since heater promotes mold growth. Just room temperature air. Sprey with Lysol spray. Be generous. That should do...

Let us know how you did... Good Luck... Milo

Thanks milo
Id like to think that the grout sealer is keeping the moisture out...
I'm sure it is.

However in applying the sealer to the grout I've effectively trapped the moisture that got through in the first place in there. That is my concern.

I'm sure it will evaporate over time but will it start to mold?

No, sealers are not water proofers. They are designed specifically to allow water to pass through either direction. Will it slow it, yes, but stop it, no. The only job of a tile and grout sealer is to help in maintaining the cleanliness and that's it. This is why a waterproofing barrier is needed between the framing and the cement board, or a waterproofing membrane gets applied to the face of the cement board and the tile is applied to that. I know it sounds counter intuitive to what is the common belief, and If anyone wants to, feel free to contact their grout sealer's manufacturer and ask them specifically if the sealer will waterproof their grout.

Your issue is not an uncommon complaint on glass tile showers that the bottom rows seem darker after using the shower. For that reason, many glass manufacturers suggest a topical waterproofer on the cement board so that there is less water being held behind the glass so drying out occurs faster. Cement products; thinsets, grouts, cement boards, and tiles; glass, glazed ceramics, stone, porcelains, do not support mildew growth either. However, body soils, the binders in bar soaps, etc, do support mildew growth. The purpose of a sealer is to prevent those from filling the microscopic pores of the surface of the grout. That gives them less of a strong hold and makes them easier to clean away. The drying out of the shower back through the grout lines could provide the necessary moisture, but is not the actual cause of the mold. Using felt or poly behind backers leads to the longest drying time for the walls.

If you want a truly mold free shower there are a few things you can do...

1) A big one is keeping the fan running after a shower. If there is no fan, just a window, open the window. You want the humidity to disappear.

2) Get rid of bar soap. Bar soaps have n=binders int ehm that cause them to congeal on surfaces, and they hold along the walls all the organic materials needed for food for mold and mildew. Liquid shower soaps do not have those binders, do not congeal and will rinse away along with whatever body soils they carry.

3) Hand held sprayers. If you don't have one, install one. Prior to turning off the water, sprat down the walls. You wouldn't wash your car or pots and dishes with soap and not rinse them, but everyone does just that with shower walls.

4) Use a squeegee or a towel to wipe the walls down after use. If a few people are using the shower successively, then do it when the last person is done, but the quick spray down of walls should occur after each person.

Also, don't allow anything along the tub deck that will slow down the drying or hold moisture. A washcloth left in the corner of the tub deck or childrens' bath toys are big promoters of mildew.


I'd still like to know what you used to set your tiles. If it was mastic or anything premixed from a bucket, then there is a good chance the darkness will never go away at all unless that glass is pulled down, cleaned off and reset with the exact white thinset/additive combination that was listed in the glass manufacturer's instructions.