Limestone slabs again - Strange staining from new

[timsim]

Hello everybody,

I have had 75m2 of limestone slabs laid at the end of May this year. I am aware that they change colour with weathering and do not mind that. I now wish to apply an impregnator seal to provide protection after a thorough cleaning. However, about a dozen of the slabs have a strange sandy coloured staining which was there from the beginning but seems to have become more evident. In some cases the staining is quite sharply defined as though a slab with some staining property had been laid on it before delivery. This can be seen in one of the photos but it is a little faint.

Can anybody say what could be the cause and what if anything can be done about it?

I attach two photos.
Thanks
Tim
https://www.dropbox.com/s/s2kwudxzf2qch3x/P1010858.JPG?dl=0
https://www.dropbox.com/s/wgzdtpk4isohtpp/P1010859.JPG?dl=0

[London Stone Paving]

Its a strange one. Not seen that before with black limestone. Its probably become more visible as a result of cleaning the other slabs. It looks like natural marking to me. A colour enhancing sealant may cover it up. Can you do a test spot anywhere?

Steve

[higgness]

I have seen this, get some in odd crates here and there, but not a lot. I have noticed it more on setts than the slabs. However, I would not have laid these.
It may be some iron deposit occurring naturally in the limestone, rusting out.

[RAPressureWashing]

Had the same staining on Limestone earlier this year, no one (paver, suppliers etc ) could say when it came from or what caused it. I'll dig the photos out and past tomorrow, it is removable, not easy to do but can be done.

[timsim]

Thanks to all for the replies.

If it can be removed, Roger, then I would grateful to know how.

If I have read the very full information on this website correctly applying a colour enhancer is not a one-time process but needs repeating later. I am reluctant to get involved in this and am also concerned that it might be a patchy result. All the affected slabs are readily visible.

Because it does not seem to be something readily removed I am inclined to ask the contractor to replace the affected slabs.

Tim

[RAPressureWashing]

Here are photos of the same staining you have, really don't know what has caused this, as I said earlier paver & supplier have no idea either,
The first photo is of the paving in situ
The second is a test piece same batch that had the same stains on and after first wash stain is till there.
The third photo is after serious stain remover wash used, totally bleached the stain out, but now the hard part getting it back to Black.
The fourth photo is the slab after being sealed 3 times to achieve the level of Black needed to look natural after the treatment.

[RAPressureWashing]

Thanks to all for the replies.

If it can be removed, Roger, then I would grateful to know how.

If I have read the very full information on this website correctly applying a colour enhancer is not a one-time process but needs repeating later. I am reluctant to get involved in this and am also concerned that it might be a patchy result. All the affected slabs are readily visible.

Because it does not seem to be something readily removed I am inclined to ask the contractor to replace the affected slabs.

Tim

I can tell you the products used but to be honest they are not for a DIYer (no disrespect there) it's just that if you don't do it right and things go wrong then you have an expensive mistake on your hands. Plus it's not just the chemicals but also the right tools and machines which a home owner/DIYer would not have.

Re sealers being a one time solution no they are not in my opinion as yo will need to top-up the sealer after 12-18 months especially Black paving.

To be honest I would go with getting the paving lifted and replaced, as even if you get a professional paving cleaner in it is going to be very very expensive to do.

The test piece I did in the thread above, the colour is holding well after 3 months, the paving issue it self has not been resolved (we are just doing a test to see if the stain can be removed so have no other interest in this at the moment) as the homeowner has a lot of stained slabs and is still in discussion with the supplier & paver from what I can gather.

[higgness]

Hi Roger, do you know if the stains were on the slabs before they were laid?
Thanks

[PavingSuperstore]

That's a nice finish you have on that final picture Roger. A lot of work mind you!

[RAPressureWashing]

Hi Roger, do you know if the stains were on the slabs before they were laid?
Thanks

Yes they were, the one I worked on was one that was left over.
They are still in place as a lot of discussions are going on I think.

[RAPressureWashing]

That's a nice finish you have on that final picture Roger. A lot of work mind you!

Cheers George, yes it was a lot of work to bring this back, especially not knowing what the stain is or what caused it?

I will be trying the rust remover soon mate just not had a chance or need to as yet.

[timsim]

Thanks for all the replies and wow Roger what a lot of work to get to that excellent result.
I'll discuss the removal of the affected slabs with the contractor. If we go down the replacement path (and the alternative seems to be do nothing as Roger's process sounds horribly expensive) then it will mean buying another pack of slabs (~15m2) unless the supplier has some individual slabs available.

Can you also tell me how frequently the impregnator seal used in the final photo would need to be renewed?

Thanks.
Tim