Permanent dust on sandstone - I cannot remove the dust

[Jw2525]

Hi there, I have recently had an extension to our patio and opted for Raj green sandstone to match the existing laid 8 years ago.

The original sandstone still have good varied deep colours - the new sandstone is pretty bland, and more concerning seems to have a permanent dust effect I cannot remove. Some of the stone has the efflorescence effect around the edges but the dust is different and looks like actual colour of the stone. It is the same for the different shades of the Raj Green.

Any ideas?

[alrat]

Is the dust loose or fixed and has the stone been sealed? Is it possible a sealer has been used without the surface having been swept for dust first and it's been permanently sealed in place?

[Jw2525]

Thanks for responding, no sealant has been used yet. The paving is down and pointed in resin. They need to clean it and wait for it to be dry before applying the sealant.

It is the uneven finish sandstone, and the dust effect is along all the edges where the layers change height - if I could work out how to add a picture I would put a couple of pics on!

[Jw2525]

Ps - it is fixed. Went over the patio with a hose and hard brush - non of it shifts.

[lutonlagerlout]

even from the same supplier in 8 years a different part of the quarry may be getting worked
very little chance of it looking the same
plus the original has 8 years of weathering on it
dropbox seems to be Ok for pictures
not great but OK
cheers LLL

[Jw2525]

Thanks for the response - I get the paving will look different - it’s a conscience decision we made when not replacing the existing.

It’s more the fact the new stuff looks dusty and not sure if this is just the stone or it has mortar stuck too it.

https://1drv.ms/f/s!Ah4XDBvnxFfkhIlQLYTKWQMkabpJpw

Pics added above - first two are from the new paving and the 3rd an existing piece - all Raj green but slightly different colours.

[Tony McC]

Bear in mind that a lot of what is currently sold as "Raj" is not the same as the Rajpura Green we were getting a decade or more ago. The genuinely good paving stone was quickly worked out, and the importers started to "blend" (as they put it) a few pieces of RG with bits and pieces of similar but vastly inferior stone. Many of the so-called Raj Blend offers now on the market may contain only 10-20% actual RG stone, and even then, it's not the best RG.

So, expecting a match, or even a close similarity (after allowing for weathering) is probably a bit unlikely!

[alrat]

Although not easy to tell in a photo, it looks to me like the resin jointing compound hasn't been removed properly from the surface of the slabs and has dried on the surface, creating the dust you mention.

[Tony McC]

I'm not so sure that it *is* the after effects of overly generous use of a resin jointing mortar. That bit of eff around the edges makes me wonder about the bedding.

I'm not saying the jointing compound is not implicated at all, only that I don't think it is solely that.

Has the paving been laid onto a wettish, cement-rich mortar, and has that mortar been allowed to be extruded into the joints when the flags were placed?

[Jw2525]

Hi there, yes mortar used for bedding and it does extrude into the joints (noticed when they jet washed the paving and the resin has come away in areas.

[Jw2525]

Ps they jet washed to clean the dust

[Tony McC]

If resin mortar has come away following jet washing, then either it's an underwhelming 1-part 'polymeric' or it's nowhere near deep enough (or both!)

I reckon what you se as dust is partly efflorescence - we are having a bad year for it with all the damp - and possibly a touch of cemetitious film resulting from partial and ineffective pre-jointing cleaning. There could be a touch of resin residue thrown in for good measure, but I think the prime source is that bedding.

So: try using a good quality eff remover to see how that helps. Let it dry off for a couple of weeks, look again, and if you still think there's a possible 'dusty' look, then maybe *exceptionally careful* cleaning with a dilute cement remover, preferably phosphoric rather than hydrochloric.