Stone sealent

Hi , could anyone tell me what I need to buy for the stone topper around my pool. It's very porous and has started crumbling from the underneath into the pool. This is only 1year old and needs sealing before it gets any worse. The man who laid it has disappeared of the face of the earth after saying he would come back and treat this for us . Thankyou in advance for any recommendations.

If it is crumbling from underneath then they need replacing not treating

No it is one whole.not stones. It is a mixture that was poured into a mould . We have only had it done 1 year ago by Jorge from Jorge's pools but as I said in my post he has vanished.
I'm sorted now thanks