I had my patio grouted 3 days ago, allowed to dry 2 days, then power washed, allowed to dry. The grout was a medium gray unsanded on a lighter gray slate. Now the tile has a light haze and the grout grooves have lightened to almost white in some areas. What went wrong and what can I do before sealing?
Most grouts take three days to fully cure and even then you're warned it might take longer; you only waited two.... then you power washed it.. big mistake. You removed the top coat of grout and let it set on the tile. That's where the haze came from. Get some grout remover from your home store and clean off each tile, being careful not to get in the grout lines. Where the grout lines have turned almost white, you'll probably have to remove some or all of the grout and add new grout. You might luck out and get a close match grout stain from a tile store and apply it to your grout.
There are two likely causes of the white coloration:
Grout turning white is usually due to efflorescence, which the movement of salt or minerals to the surface of porous material (such as your grout) and forms a whitish coating. This can happen in a few different ways. The most common reason is moisture from the ground below the slab, but grout may also turn white from the rain in outdoor installations, or in rare cases from water used to clean the floor.
Another possibility is that grout containing polymer was used and exposed to too much water before the polymers had a chance to combine. According to the Tile Council of North America (TCNA), “grout mixed with too much water or cleaned too soon, or cleaned with excess water can cause the polymer to migrate to the surface. In many cases (but not all), these polymers are white in color. When the excess water evaporates, the white polymer is exposed.”
I think the latter is likely your issue. Staining the grout or scraping it out and replacing it are two options. Another is to just wait a while and see if natural weathering leave you with a satisfactory appearance.
If you have a glazed or other non-porous tile, wipe them individually with a damp cloth to remove the grout residue. Use a masonry solvent, following the manufacturer's direction, if necessary. Porous tile may require more diligent scrubbing or just time for weathering.