Limestone tiles

You must skim the back of the tilesbefore lay on adeshive. Also for limestone tiling not enough to use S1.

Limestone tiles are incredibly porous so colourants contained in adhesives and grout can, and will stain them. You can seal the back of the tiles before laying with SBR which will prevent this and also help bonding, however, as this hasn’t been done I would suggest leaving them 7 days to dry completely and then look to see if an acid wash will remove some of the top level of discolouration. If that doesn’t work then you could apply a sealer which has a colour enhancer in like Lithofin MN stain Stop plus as that might make the discolouration less noticeable. Sorry not to have any better news and I hope that the manufacturers are right and the staining will disappear as they dry.

White adhesive part 1 flexible fibre +

You must apply on tiles first and assure the floor is prepped properly before work commence

S1 Adhesive is perfectly acceptable so long as the substrate prep is correct. As said by another, back buttering is a must, but that is just true of all floor tiling especially. being a porous stone there is always a chance that it is moisture that was already In the tile from manufacturer, or from poor storage in between being shaped and being sold. Do not seal the tile, and if already sealed then remove it, this will allow the moisture to escape. Give it several weeks to fully dry. Tell the customer to refrain from soaking the area I. E. Mopping. It's difficult to answer this without seeing the colouring of the stone before and after laying. It's also worth noting this is a natural product, and limestone can have naturally darker veins of mineral in it.