QUESTIONI'm working on a house with Saltillo tile that is 50-70 years old. We've scraped ,cleaned with acid, vinegar...and pressure washed. The tile is interior, my question is; I'm fairly sure there isn't a waterproof barrier under it, therefore, after I seal the tile, will the white film surface every time it rains or my slab gets wet?
ANSWERANSWER - Sealing a Saltillo tile doesn't waterproof the tile. Sealing the tile only makes it moisture resistant. A sealer should help to minimize the white efflorescence staining, but it may or may not stop it. It depends on what the tile and its substrate is subjected to in terms of moisture from high water tables or from water migrating towards the concrete slab where it can migrate up into the slab and into the tile.
The sealing is temporary and depending on the type of sealer and what type of weather and foot traffic it is subjected to will determine how long the sealer will be effective. Once water doesn't bead up on the sealed surface and it leaves a wet spot on the tile, then it is time to reseal, which could be every 6 months to a year on average.