Hello Tom: Just discovered your web site. Its great. I have 1″ polished china white marble hex on my new bathroom floor. Before using the shower, I cleaned and sealed the floor with a Solvent Based impregnator/Sealer. Over a couple weeks I put three coats in the shower area (I was waiting on the glass panel).
Now after three days of use areas are turning grey (like the “White Marble Gone Grey” question on your site); however this was pretty much white to begin with. It seems like moister is getting to the thinset. Did I use the wrong sealer? Do I need to pour it on thick to get it in to the grout since there is so much grout with a 1″ hex? Do I know need to wait for the greying to dryout before I reseal? Secondly I too have the same problem as with White Marble Gone Grey question. My walls are a 5″x2.5″ Polished China White marble. I waited a couple weeks to let the thinset dry prior to sealing and resolved at the time that there was going to be some tiles greyish and some more white. I sealed the walls and now I’ve read your response to the “Gone Grey” question. Have I forever sealed the moister in? Will it eventually dry out, albeit slowly? Could I apply heat with a salamander to draw the moister out of the tiles even thought its been sealed.
Basically the sealer is not working effectively in the grout but it is working on the marble. The water is soaking into the grout and wants to wick out the marble; however, the sealer is blocking the moisture from evaporating. I am sure that you probably guess this by the way it looks.
The problem is two-fold. First all, the sealer is probably a high viscosity sealer that is commonly used to penetrate the tight pores of natural stone. With non-sanded grout joints this works well as long as the grout joints are sufficiently sealed as well. However, with sanded grout (common with joints over 1/8″ wide) the low viscosity sealer just wants to suck down in deep in the grout and leaves the grout surface unprotected. You can test this by simply wetting the grout and seeing if it becomes darker. If it darkens, then the grout is not sealed sufficiently.
Secondly, grout joints, especially in mosaic patterns, are difficult to grout because they are slightly concaved from the marble surface. As you wipe on the sealer, you miss the grout surface. Combine this with a low viscosity sealer and you basically have no sealer on the surface layer of the grout.
For the fix, here is what I recommend. First you need to see if you can pull the moisture out of the marble by using a salamander heater or equal. It could take several hours and a few tries. Given that you have applied several coats of sealer, this might not work at all. In that case, you need to effectively decrease the volume of sealer in the marble. Do this by cleaning the surface with Acetone, sponging it on the surface and letting it sit there for about 20 seconds before wiping off. This should allow you draw the moisture out with the salamander heater. If the tiles do not turn back to white, then you have probably sealed the moisture in before the thinset or the grout fully cured. If this is the case, you need to try Acetone again and heat until the moisture mark are gone. You need to wait a couple days after they finally disappear because they will dry on the marble surface first, and then deeper. If you think they are gone, wait a couple days to see if a little more moisture wicks to the surface.
Finally, you have to re-seal the grout. I’d recommend using a higher viscosity natural stone sealer like Miracle Sealants 511 Porous Plus or equal. Don’t be concerned with sealing the marble, just focus on the grout. The marble mosaic will get covered if you just worry about sealing the grout. Watch for all the grout to darken from the sealer as you seal it to confirm the sealer has contacted it. The grout color will come back to normal once the sealer dries. Let is dry for 24 hours before use.