how to seal cement tiles?
I am in desperate in need of sealing advice for a unique situation.
We recently installed hand-made cement tiles -- also known as "encaustic tiles" or "carreaux de ciment" -- in our kitchen. (If you're wondering what these are, see description below.)
Our tile retailer -- Mosaic House in NYC -- warned us in advance that cement tiles are highly, highly porous and therefore require much more diligent and copious sealing than just about any other flooring surface out there, including almost any natural stone. He recommended an oil-based impregnating sealer called Protex by Tenax. Accordingly, we purchased 2-3 times the amount of Protex that Tenax recommends for natural stone, and gave it to our installer with all the same admonitions we heard from the retailer.
Our floors are STAINING LIKE MAD! A bottle of aged balsamic vinegar broke on the floor and literally stripped the pigment right out of the tile! Clearly it was the acid in the vinegar that did the damage in that case; in fact there was no trace of the dark stain you would expect from dark vinegar. It looks like a photographic negative of a stain. Elsewhere on the floor are some small dark spots (oil?), several light spots (more acid-stripping?), and a few colored ghosts of other items that stayed there too long, like drops of black bean liquid.
The retailer feels certain the problem is that the installer did not fully impregnate the tiles -- a common mistake among installers not familiar with this material. It's true that the floor never did pass the "beading water" test . He suggests we apply more coats of Protex until the tiles can't accept any more (and water beads on the surface). Then for added protection give the floors a light waxing (with a mop and water) once a week or so.
1) Can I apply more Protex over what's already there, as long as I clean the surface well? Or do I have to strip off the existing sealer first?
2) Is there another sealer I should try? Not only did the Protex let us down (though it may have been under-applied), it is extremely expensive ($75-100 for 1 liter!) and very, very hard to come by (no local retailer, and only one or two online).
3) If I switch to another product, does it have to be oil-based? I have heard that one shouldn't put water-based sealers over oil-based ones. Is that true? Is oil-based always better for this type of situation?
3) Could the acid in the vinegar have stripped the sealer itself, before leeching pigment out of the tile? In which case, should I be looking for a sealer that is specifically resistant to acid?
I apologize for such a long-winded question. I am hugely grateful in advance for any advice anyone can offer.
PS -- I want to add that in spite of above, I am still crazy about these tiles. They are old-world beautiful and unique, like a one-of-a-kind Persian rug; they are visually complex yet with a totally matte, flat surface; they require the thinnest of grout lines (only 1-2 mm); they provide much greater-than-average thermal mass for radiant in-floor heating; they are impervious to scratches from my dog's claws, unlike my wood floors (which I otherwise love); and they come with enough natural, hand-made imperfections to make other imperfections -- like nasty vinegar stains -- blend in surprisingly well. Not for everybody, but definitely for me.
Description of cement tiles: You may have seen them in Europe or Latin America where they've been popular for centuries. They are not glazed or fired. The design comes from powdered marble containing different natural pigments which is poured into a copper mold of the design, then "backed" by portland cement and other materials to form a heavy, perfectly flat, 5/8"-thick tile, usually 8" X 8". Each tile is then compressed at extremely high pressure and left to cure for several weeks. It often takes four tiles, comprising a 16" X 16" square, to form the basic pattern for the floor design.
Here is a link that might be useful: a kitchen floor of cement tiles