Natural sandstone is a porous, soft stone that allows moisture to pass through its surface. It is advised to seal your pavement because of this. This shields the stone, stops any stains and helps stop the build-up of unwanted growths like algae, moss or mould, which flourish in damp situations. Your stone slabs can be treated before you install them to keep them from being stained, or you can wait a year before applying the sealant to give the stone a beautiful weathered appearance.
Depending on how porous your sandstone has grown, it is advised to seal it periodically. Generally speaking, you should seal your sandstone every year if it quickly absorbs water. This can be repeated every three to five years if it takes five to ten minutes for the water to soak.