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We recently moved into a home that has slate tiles in the bathroom, but the tiles don't seem to be well-maintained, and they have several areas where the lacquer finish has worn off, probably due to water buildup.

What would be the best way to fix these areas? Is there a product that I can apply that will effectively refinish the problem areas and restore the color to the tile? I'd like to try to avoid having to strip and refinish the entire floor.

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I actually did a spot test on one of the tiles where I etched off the problem portion and applied some sealer (TileLab sealer & finish), but it turned the color just ever-so-slightly darker, and nowhere close to the original dark green color of the rest of the tile. What could be going on?

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I would start with a light acid etch or whatever you do to reseal and bring a shine out will magnify the surface scum/ effervescence. I use muriatic acid and water with this I would start out with a weak solution 30:1 with possibly a max of 15:1.

I would mix up a small batch remembering to always add acid to the water AAA to prevent a thermal reaction that happens if water is added to acid.

Safety glasses and rubber gloves will be enough safety gear and a good idea to have the vent fan on or window open. I would sponge the areas staying away from the grout or not etching the grout as heavily. Once the surface looks good rinse the sponge and then rinse the etched area at least 3 times and make sure it is fully dry Pryor to coating with a quality sealer.

The reason I suggest trying not to etch the grout it may really change colors and then the entire floor would need to be etched so the color will match. Start with a weak solution and possibly 2 or 3 wipes of fresh solution prior to going stronger is the best advice I can provide.

Muriatic acid can be found in pool supply stores and most lumber / big box stores as this is commonly used to balance the ph in pools and to etch concrete and stone products.

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  • Thanks, please see updated question. – Dmitry Brant Nov 17 '19 at 20:11
  • It may take quite a few coats the hardest part is getting any residue off, muriatic usually works well for me. In some cases the stone has been waxed with acrylic wax to really bring out the shine I don’t care for wax on tile as it doesn't age as well on the grout, but to give a more translucent finish this may be required. – Ed Beal Nov 18 '19 at 1:11
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What does it look like wet? That will give you a good idea of what it will look like with new surface sealer. If it looks enough like the rest, just reseal or varnish it.

Ok. It still looks too light.

Look at the light areas with a magnifying glass, while poking at it with a knife or the corner of a chisel you don't care about. You want to play with the edge of the different colour.

If you can pick up flecks of light, showing the original colour, then your light stuff is efflorescence -- lime transported by water through the mortar or grout. You will probably find this on the grout too, but it's a better colour match so won't be as visible.

If you can scrape up flecks of dark revealing more light, then the original stone is that lighter colour and it was stained.

First case: See other answer regarding using acid to remove. Note that at low dilutions it may take a very long time. As long as you see it bubbling, it's removing stuff.

Second case: Get green and black paste or liquid form aniline dyes, and a can of compatible varnish (if the dyes are in oil use an oil based varnish, if in water or alcohol use a water based varnish. Water base will dry faster. Oil base is somewhat easier to work with.

Pick up some small water colour brushes.

Using jars like baby food jars measure out about 30 grams of varnish. Start with 1 gram of dye. (Food scale for this.) Turkey baster works well for moving small quantities of varnish from can to jar. If you measure, then you will know for next time and can make another batch that's the same.

Experiment initially on paper, until you get a green that is both lighter than the tile and greener than the tile. Suppose you find that that takes 1.5 g green dye per 30 g varnish.

For your black, start with half that.

Now, on paper see if you can reproduce the look of your tile.

You want to use a mix of colours since the tile is not a continuous colour but is made of blobs, some greener than others. Once you think you've got a handle on this, go to the Big Orange Box and buy a single tile similar to what you have. Play with painting that.

You want to build into the colour slowly -- should take 2-3 coats playing around with both colours to get a match.

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