We built a patio using 1″ thick natural sandstone pavers, which were laid on 4″ thick stone dust, i.e. the pavers have not been mortared in place. When we installed the first small section years ago, it was beautiful, but the stones were quickly stained and darkened as algae and other growths invaded. We had considered sealing the stone ahead of time, but a young man who worked for the original vendor told us that “sealing the stone would cause huge problems because sandstone is porous and if sealed, the stone won’t be able to breath, trapping moisture underneath etc.”.

We have just expanded the patio considerably, so I am investigating what we need to do to correct the situation. One year ago we added a couple steps onto the patio where we mortared the sandstone to landscaping blocks. Looking at the steps today, it is evident that mortaring sandstone in-place helps prevent moisture from entering the stone from below, so for new steps I’m building (other side of patio), I will do it the right way. But, sadly for the large main patio it’s too late to pour a cement slab and mortar everything in-place ? Therefore, I am revisiting the question of sealing. I have just been told by 3 stone vendors that sealing sandstone (that’s been laid on a bed of rock dust) is fine. So, now I am totally confused – can someone please shed light on the situation for me? Is it safe to seal non-mortared sandstone pavers in an outdoor patio, or will this cause large problems?

Thank you in advance – any help, guidance, or even opinions will be greatly appreciated!!