Black limestone stains

[Kevin22july]

Hi all
I laid a full patio with black limestone last October on a full layer of concrete. I didn't use grout and used joint it simple. Brushed it in then soaked it.
From day 1 the patio had a silver grey look and never looked black.
I was advised not to seal for 12 weeks and to make sure it was dry. Not easy living in Cumbria. However a month ago I decided to power wash it with a mild non acid detergent. After drying I was left with several horrible white stains as shown in the pictures. Can anybody advise me how to remove these stains as scrubbing them doesn't work. Or if I now seal them will the white disappear. Thanks

 

[Kevin22july]

Hi all
I laid a full patio with black limestone last October on a full layer of concrete. I didn't use grout and used joint it simple. Brushed it in then soaked it.
From day 1 the patio had a silver grey look and never looked black.
I was advised not to seal for 12 weeks and to make sure it was dry. Not easy living in Cumbria. However a month ago I decided to power wash it with a mild non acid detergent. After drying I was left with several horrible white stains as shown in the pictures. Can anybody advise me how to remove these stains as scrubbing them doesn't work. Or if I now seal them will the white disappear. Thanks

View attachment 124177

View attachment 124178

Sorry cement not concrete

 

[Ajax123]

Cant advise on sealers but its out doors on concrete which is presumably not on a DPM. How on earth do you expect to ever get it to dry let alone in 12 weeks and as you say especially in Cumbria???? As for the marks they are simply where water, probably rain, has puddled and run. It has soaked into the tile and then evaporated leaving the soluble salts behind. the grey look is probably an element of the same but tinged with efflourescence.

 

[Kevin22july]

Thanks AJAX. There was no DPM.
It did dry out in July that's when the white marks appeared. Any advise on how to get rid of them before I seal. Thanks

 

[Ajax123]

Removing the marks is probably a job for a tile stain remover but this in itself could lead to more staining as there will be moisture in the tiles full stop. In choosing a sealer you will need one that is capable of dealing with rising moisture from underneath. for that youd be better speaiking with a specialist... dont know if Lithofinbob still hangs around the forum....