Dark stains on granite slabs

[lozwhite]

Ive just laid a large patio using white patara granite slabs which i bought from B & Q,they are 600 x 600 and approx 1inch thick. Dark circular patches have nowappeared on the top of the slabs in each corner and the centre of the slabs which is obviously where i put the cement when laying them. i presume it is damp coming through as whenever they are completely wet after the rain the slabs go that colour all over, the patches only become visable when they dry off. im thinking now that i should have used a dry mix or had the slabs sealed before laying them but didnt know this would happen until half the patio was down as B & Q never mentioned it when i bought them. Does anyone know if there Is there anything i can do now to get rid of these patches as i dont want to redo the whole patio and the slabs were pretty expensive so im a bit done that they dont look right?

[lutonlagerlout]

did you read this page before starting?
also granite needs sealing same as any other natural stone
lithofin MN stainstop is the kiddie about £25-30 per litre
LLL ???

[Tony McC]

Some of the Chinese granite is notoriously porous, and that's the primary reason for the darkened appearance. Also, from the sound of it, you've used the dreaded spot bedding, so some would say you deserve this outcome.

The best way to avoid damp patches on the G603 and similar Chinese granites is to lay on an exceptionally porous bed of 6-3mm grit, or very coarse grit sand, with just a touch of cement.

[lozwhite]

so i take it aside from relaying the whole patio in the way that you have explained there is nothing i can now do about it?

[lutonlagerlout]

sadly yes loz
LLL

[bennett]

I have also had a problem with staining on light coloured granite slabs the slabs were laid on a full bed. When wet slabs all look the same when dry some have staining. Thinking of putting on a colour intensifier such as lithofin or the stain stop plus, anyone no if this would work and how long does it keep its colour before doing it again.

[Tony McC]

The colour intensifier should minimise the problem, but I've not seen it done, so I'm not sure just how effective it would be. I'd be very interested to hear, though.