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Posted: Sat Aug 15, 2015 4:57 am
by RebRob123
We had some new Indian Sandstone slabs laid Mon-Weds, with Geo-Fix being used as the jointing compound. All seemed fine until it rained on Thurs and obvious black marks appeared along the side of some but not all the slabs. This hasn't occurred along any of the previously laid slabs that were being repointed. Does anyone know what may be causing the unsightly black marks to appear and importantly know what can be done to get rid of them? The company who laid the patio hasn't seen this occur before and I'm not necessarily of the opinion it's their fault. Just looking for an explanation and solution. Thanks!
Posted: Sat Aug 15, 2015 10:11 am
by mickg
Posted: Tue Aug 18, 2015 12:14 pm
by Tony McC
Geo-Fix is a jointing compound? Who knew? I thought it was an expensive skip filler! :;):
The staining, as you describe it, is probably what we refer to as picture framing. It's quite possible that some of the resin from the Geo-Fux has been carried into the stone, especially so if it is a cheap'n'nasty incredibly porous sandstone such as Mint or Rainbow.
I'd lose the Geo-Fix (it will fall out if you sneeze on it) and replace it with a good quality mortar, either a genuinely good polymeric or a 2-part epoxy mortar or a 4:1 wet mix of sand and cement. The sand/cement is cheapest; the 2-part epoxy probably the easiest for DIYers.
Posted: Tue Aug 18, 2015 12:46 pm
by RebRob123
If we removed and replaced the Geo-Fix would the black marks disappear or has the Indian sandstone been permanently damaged?Thanks!
Posted: Tue Aug 18, 2015 2:23 pm
by London Stone Paving
are you able to provide any more information on the marks and the type of stone? A picture in this case would tell a thousand words.
It does sound like picture framing from what you have said but picture framing doesn't usually leave black marks
Steve
Posted: Wed Aug 19, 2015 2:09 pm
by Tony McC
As Steve says, we'd need to see the black marks to determine whether they were just damp or summat more serious. Upload a photie or send one to me and I'll upload it for you.
Posted: Wed Aug 19, 2015 8:36 pm
by RebRob123
Apologies for the delay but hopefully these photos can be seen okay. Thanks.
Flikr
Flikr
Posted: Wed Aug 19, 2015 9:06 pm
by London Stone Paving
Are you absolutely certain that the marks appeared post installation?
The reason I ask is because I have not seen polymeric jointing compounds cause that kind of marking. You also said that only the new slabs are affected.
It looks to me like the type of damage that occurs while stone is packed inside a crate. Can be caused by nails from the crates rubbing against the stone during transit (which is a long time from India these days, they are driving the boats slower to save fuel)
Can you have a look and see if there is any physical damage to the stone in the blackened areas
It could also be caused by foam or some other kind of packaging material that has been rubbing in transit.
Looks like a packaging issue to me
Cheers
Steve
Posted: Thu Aug 20, 2015 12:03 am
by RebRob123
Thank you for your feedback. On close inspection there appears to be no obvious damage to the stone. I know it's impossible to say definitively but if it's foam or packaging related do you think this may fade over time? If it were your sandstone what would you do? 
Posted: Thu Aug 20, 2015 8:45 am
by London Stone Paving
Have you tried to clean it off yet?
If it is what I think it is then a jet wash will shift a lot of it. You then may need to use a cleaning product to remove the remaining.
Something like Lithofin outdoor cleaner. May need a couple of applications to shift it all
you also need to take care not to damage the pointing when cleaning with a jetwash. Best to get a rotary head attachment rather than using the lance of the jetwash
Cheers
Steve
Posted: Thu Aug 20, 2015 9:29 am
by Tony McC
It looks like the sort of staining seen when flags are stacked on edge in a crate that's very recently been dipped so the nastikemmickle they use to treat/fumigate the timber gets absorbed by the stone.
It often doesn't make itself obvious until a wet jointing medium is used which acts to drive the nastikemmickle deeper into the stone and out to its surface. You can often observe that the separation between individual stains matches the separation of timbers in the packing crate.
I've only ever seen this with the real "budget" imports, where there is little or no oversight of the export preparation so the packers can get away with all sorts of nonsense, including using a particularly nasty sort of creosote-like goo to stain the timber and give the impression it has been fumigated. When you buy syone from a 'name', they tend to micro-manage every stage of the stone's preparation and export in order to protect their reputation, but then there are hundreds of suppliers who gleefully sell containers to anyone with the money, and it is usually a case of they get what they are given.
Now, it strikes me that if someone is stoopid enough to use the Geo-Fix rubbish, they are probably buying stone as cheaply as possible, and so they may well have, completely inadvertently, ended up with stone from a cowboy exporter.
I'd go with Steve's suggestion - try a power washer, and add a bit of Baby Shampoo. The stain is probably oil-based and the soap will act as a surfactant, helping it to disperse.
I'd definitely want to know how you get on......
Posted: Thu Aug 20, 2015 4:53 pm
by RebRob123
Thanks. Will try this and update you afterwards. How long should we leave it between the patio being laid and attempting this?
Posted: Thu Aug 20, 2015 9:13 pm
by London Stone Paving
Think you've hit the nail on the head Tony. On close inspection you can see where the creosote has absorbed into the flags.
I have known people in the past who have removed oil stains from stone by covering the stone with plaster of Paris an then covered the area in cling film. Condensation occurs and the plaster of Paris draws the moisture and oil stains out of the stone. This method may be worth a try as well
Steve