Which stones need sealing?
Sawn and honed sandstone benefits most, because cutting opens the pores. Riven sandstone, limestone and Kota stone all benefit in high-traffic or food-preparation areas. Basalt and granite are far denser and often need no sealer at all.
Should I seal before or after laying?
Before, on all six sides, for sawn paving. This is the single most effective step against efflorescence and picture framing. A top-up coat after laying and grouting finishes the job.
How often does it need redoing?
It depends on traffic, exposure and the sealer used. A simple field test: splash water on the surface. If it beads, the sealer is working. If it darkens the stone, it is time to re-coat.
Will it change the colour of my stone?
An impregnating sealer is designed not to. Some products are sold specifically as colour-enhancing and will deepen the tone. Always test on an offcut before committing to a full patio.