Sawn sandstone - Is it pourous

[London Stone Paving]

That makes perfect sense about not sealing the underside.

Changing the subject a little bit does concrete paving absorb water and if not how it does to adhere to the bedding layer?

[lutonlagerlout]

we are missing the point here
most paving doesnt need to adhere to the bedding
only steps and paving at a free edge has to be *stuck * down

SBR is your friend in these scenarios
LLL

[Tony McC]

LSP - yes: concrete paving absorbs water.

LLL - you're right, but the thin stone flags now widely used for patios just don't have sufficient depth or mass to keep them in place, and so adhesion to the bed is more important than it would be with, say, 50mm thick 3x2s.