Polished Porcelain/Discolored Grout? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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Higher Standard Tile
10-11-2003, 10:14 AM
Has anybody else ran into this problem before? I'm installing a polished porcelain tile on walls and a ceiling from Caesar. The tile is installed with a polymer modified thinset (white)and the grout is a polymer modified unsanded (biege). The grout joints are 1/16". The installation was grouted 24 hours after the last tile was set and the grout joints were cleaned out before grouting.

The dicolored areas are 1-2" long , it appears the grout hasn't dried but it has. The areas that are discolored are usually on the bottom of the tile 1" in from the corners.

I noticed that there is a small strip of wax on the back of the tiles so that they do not scratch the porcelain finish in the box. (They are about 1" in from the edge of the tile) Usually these just flick off but these strips are not easy to scrape off. Is the thinset causing the strip to dissolve and leach into the grout joint?

The problem only occured on the walls, the ceiling looked ok. Also one wall that had cured 48 hours did not have as much discoloration. I was able to fix it by scraping out the discolored grout and regrouting. Could the problem reoccur once the shower starts to be used? Does anybody else have any ideas on what caused the problem or what can be done to prevent it? Thanks.

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John Bridge
10-11-2003, 05:09 PM
The discoloration is probably only on the surface. I would have used sanded grout with the porcelain tiles, but that's water under the bridge. Just scratch out the affected areas and re-grout, or scrub with a light acid. Sulfamic is my fav because you can't over-concentrate the stuff. I think you can get the crystals at Home Depot.

Acid. Wear eye, ear, nose and throat protection. Rubber grubs, too. Open the window. :)

Higher Standard Tile
10-12-2003, 05:19 AM

The discoloration is not on the surface but throughout the depth of the joint. The majority of the grout looks fine just these few areas are darker than the others even though I let the grout dry a few days before scraping out the darker sections.

It may be water under the bridge but why do you use sanded grout with polished porcelain? I always use sanded or epoxy with matte finished porcelain but tight joints look best with polished tile. Also will the sulfamic acid damage a polished surface even if it is porcelain?

10-12-2003, 09:38 AM
I think it's caused by the joint drying out faster in some areas than other areas. I've had it happen when using standard 4 1/4 wall tile and unsanded grout (other than white). With 4 1/4, some of the tiles have glaze on the edges and won't set up the joint. On porcelain I've never had the problem but I use sanded grout.;)