New sandstone patio has 'checkered' dark patches

[jfender]

Hi, last March we had sandstone slabs laid on top of existing concrete. They were not fitted on a new bed of continuous cement but a grid-like structure of cement. It all looked great at the beginning but I think moisture was trapped in the 'holes' where there was no cement. Some of the larger slabs have had 8 dark squares permanently showing, and when the weather is wet the whole patio has a 'checkered' look. It's pretty ugly, and I'm rather disappointed. I'm hoping there might be a sealant that will disguise this look/prevent rain entering these holes, though I guess moisture could also be coming up from underneath? Any advice/thoughts welcome. Thank you. Would love to post a photo but not sure if this is possible on here ??

[seanandruby]

sadly this is what your dealing with

[jfender]

I wish I had seen this website before getting the work done is there not a sealant that would reduce the look of the dark damp patches???

[Tony McC]

It's reflective staining - no known fix, sadly.

[jfender]

Thank you for your reply. My patches however are not where the cemet is, but rather above the gaps where there is no cement. Would maybe a colour enhancer sealant be worth trying? A sealant that would prevent moisture from penetrating the slabs and collecting in the gaps? Any advice very welcome.

[Tony McC]

No - that's still reflective staining because the mineral carry-through from the mortar spots is limiting the ability of algae/lichens to establish themselves on the flag surface. Think of it as a sort of 'negative' of the more commonly seen reflective staining, so no colour enhancer, no sealant, no blck spot remover, no magic jollop whatsoever is going to rectify the situation.