QUESTION

Ring Spots in Stone - I am from auckland new zealand. I own tiling contracting company. recentley had a job to install basalt 600x400x10 onto compressed sheat (cement board)to walls in main lobby. supplyer of tile adhesive Mapei New Zealand had specified Kerabond + Isolastic (cement based adhesive). after an water washing the stone showed ring shaped spots of moisture ( three month later it's still there.

i've reversed process by making one sample tile spot fixed,after few day of cure i've wet it - showed same affect,left it in the open air area and it dissappered. Lobby area is quite enclosed, which i think slowimg drying process.can you please give me some idea how to treat it. Basalt is vulcanic stone.
many thanks

ANSWER

ANSWER - I'm not sure what type of product Mapei Isolatic is. Since it is being added to Kerabond it must be a latex additive.

The ring shape spots of moisture suggest to me that you may have spot bonded the tiles, which isn't recommended. The tiles should have full thin-set contact. The spot bond areas are probably retaining moisture and the moisture is migrating into the stone at those locations, and until they dry out the spots will show. Basalt is normally very dense, so I'm surprised that the stone is absorbing, but you implied that the stone does absorb.

If you said the adhesive was a mastic then I would think that the oils in the mastic might have migrated into the stone, but that would not dry out.

The only way to speed it up is to heat the tile at those spots and see what happens. Consider using an electrical heat gun with high heat intensity and see what happens.

Good Luck!