marble shower caulking issue

sgouldDecember 8, 2010


we re-did our bathroom last yr, we had customized shower pan made from marble tiles, and shower wall is marble slab. We had a decent licensed contractor doing the job and it passed all the inspections. One issue keeps coming up w/shower caulking. We re-applied the caulking a few times, for some reason, the old white caulk BEHIND the (sealed) gray caulk, is still getting wet/damp somehow, and breaking the gray caulk? It happened even after removed all the bad caulk, and dry things out w/ denatured alcohol & hot air, and re-seal w/ new caulk.

No idea how this could happend.

would it just be condenstation/moisture from the regular air, in the wall, onto the back of marble? or some wicking through the marble walls, or grout? (we do squeegee dry the shower walls and floors, most every time...)

Thx for any input!

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Marble is rather porous -- so water is getting into the stone.

How was the stone sealed? That may be the issue.

More importantly -- how was the shower built? what kind of waterproofing materials/memberanes were used?

    Bookmark   December 8, 2010 at 5:32PM
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I'll throw something out from left field...

If you have a continual run of white "caulk" coming out from behind the wall, it might actually be mastic.

Marble isn't usually installed with mastic. But if it was, the mastic can re-emulsify and creep down the wall and show itself at the bottom caulk line.

It's one of the horrors that I've seen over the years, which is why I thought I'd throw it out.

    Bookmark   December 8, 2010 at 9:07PM
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It was sealed with Aqua Mix Professional Sealer's Choice Gold, recommended/provided by the slab dealer. It says provides up to 15years stain resistance. It says for all natural stone, does allow some vapor transmission.

The old white "rotting" caulk is on all sides, under the showerhead/pipe wall, the side, and rear pony wall; they all get different amounts of water, and we squeegee the walls & tile floor clean each shower.

The shower pan was custom built, with concrete sloped base per code, thick plastic liner (which passed leak test), mortar bed, marble tiles on top; the walls are solid slab pieces, over Hardibacker wallboard, with tar paper overlapping w/ the plastic liner, etc

Another contractor removed most all of the old grout, sealed it with new pure transparent silicon caulk, last week.. and over the last week of use, one spot has started swelling/"rotting" again.

    Bookmark   December 8, 2010 at 10:25PM
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Forgot to mention, the slab was secured to the hardibacker wall with epoxy, no mastic etc as far as I know..

The slabs have a decent gap (max 1/4") in some spots between the bottom tile/grout (I did feel a bit of slight breeze/draft when I pulled all the old grout old and let it dry, on a cold day..? the wall is insulated)
We never have standing/pooling water at the edges; we don't tend to spray the wall with the showerhead, it is just incidental spray bouncing off us etc. The rear pony wall has much less drops/spray on it, but also had the same "rotting" problem.

The rotting spots come up in different parts, seems to be where they weren't able to clean the old caulk/whatever out as much. Before this try, most of it seemed pretty good, except for 4 spots... different than last time...

    Bookmark   December 8, 2010 at 10:37PM
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Also, the grout used between the 12" (same) marble tiles, was epoxy based as I recall... I don't see any darkening or "water spots" on the marble slab walls, eg lots of water penetration (I've seen that temporary effect on our same marble countertop, eg if left a water glass there... same sealer)...
I wasn't sure if the contractor put too MUCH sealer on the walls, it seems to have collected a bit of white haze in some of the crystal sections (it is calacata verde)... but would think that would keep more water out, if so?

    Bookmark   December 8, 2010 at 10:49PM
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