Sandstone Paving Problem

Dear Sir, I located your site via a web search. I would appreciate your appraisal regarding a problem I have with my sandstone paving. The stone is a hard sandstone from India. The pavers were laid on a sand and cement bed on a concrete slab around a swimming pool which is salt chlorinated. The stone was not sealed but after a month or so a few pit holes up to 10 mm diameter and 2-3 mm deep appeared in the surface. I then applied 5 coats of a penetrating sealer manufacturerd by a local company. The supplier and installer had recommeended sealing the stone. The sealer apppeared to do a good job since the stone no longer darkened when it got wet. Since then portions of the stone surface have badly flaked off, many pits holes have appeared and there are many areas that have a white dust on the surface. Could you please advise what can be done to restore the stone and to stop the constant deterioration. I look forward to your response. Thank you very much. Andrew Burton

 

Dear Andrew:

Have you ever heard the expression, “wrong stone for the job”?

I guess I don't need to explain what it means, do I?...

Many sandstone (actually most of them), are not suitable for a project like yours, and no miracle in a bottle could ever do the first thing to turn the wrong stone into the right one. You may get an apparent improvement, but soon the ruthless truth will come to the surface.

And, BTW, as a good solid principle, you should never apply an impregnating sealer or any other sealer to outdoor stone installations. Even stones that are suitable for outdoors may develop problems if their natural osmosis gets somehow slowed down by an impregnator.

Ciao and good luck,

Maurizio Bertoli