Cracking grout on pebble shower floor

Haviland.123March 29, 2012

A contractor installed a pebble stone (river rock) floor in our shower last year. We had to wait a year to save and install glass doors before we could use the shower. Unfortunately, a month into using it, the grout started to flake and crack. I repaired the problem areas but then started to notice, when the grout was wet, micro-cracks running along grout lines (these appear more as faint lines). When I started scrapping away at the wet grout, I discovered that water had seeped right through the grout and that the adhesive was spongy in parts. I later found out that the contractor hadn't applied a sufficient amount of sealer down. He used Polyblend sand grout and grout and tile sealer from the TileLab. I'm pretty sure he bought these at Home Depot. The tile sealer says porous surfaces need more than two coats, but the contractor had stopped at two coats. Can I get away with simply applying more sealer to the floor? When dry, the shower floor pebble tiles seem very solid; however, they have a bit of soap scum on them. Is there a super water tight sealer I could put over the existing sealer?

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I think you need to know what sealer was used initially, I don't think you put water based sealer over solvent based, but I will leave that to the tile experts to weigh in on. Our tile guy told us to flood the floor with sealer, give it 15 minutes to absorb, then wipe up excess, allow that to dry and repeat until the tile and grout will not absorb any more sealer.

But, I'm not sure lack of sealer will make grout crack, sounds like it was mixed too dry- did you call the tile installer or the GC and ask them?

    Bookmark   March 29, 2012 at 6:46PM
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Seldom is it mixed "too dry." Most often it is mixed too wet. The real problem is that, with a pebble floor, there is a LOT of grout down there. It should be mixed on the dry side and properly sealed about three days later. Custom's "Polyblend" is a generic, cheap grout.

I would have used either an epoxy grout like "Spectralock" or a urethane grout like "Quartzlock" but I guess it's too late to do that.... Tearing the old grout out can be a real Bear...

    Bookmark   March 29, 2012 at 8:56PM
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Thanks for the replies. My other concern in this is that the pebbles pop out of the Thinset when I scrape out the grout. I'm worried that the water seeping through the grout after the 20 or so showers my family took might have weakened the adhesive properties of the Thinset. Any ideas out there? Also, can anyone recommend a long lasting sealant?

    Bookmark   March 30, 2012 at 9:25AM
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I discovered that water had seeped right through the grout and that the adhesive was spongy in parts.

REAL thinset is cement based and will not become spongy when wet. Sounds like the installer may have used mastic to install the tiles - a real no no in showers. Also, there is no problem with water "seeping" through grout. That is normal for a shower.

    Bookmark   March 30, 2012 at 12:35PM
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