Cleaning black limestone - Heyllllp!

[Ian Mack]

Last weekend some builders laid some black limestone slabs for us as a new patio. There are some mortar marks left on it -not a lot, but enough to show, especially on the edges near the pointing. There's also some ground-in dirt and a 1" blob of WD40 in one place.
The builders told me to wait a week and then use brick cleaner to clear the mortar, which I duly bought, but haven't used. The type I bought was a 10 percent hydrochloric acid mixture. My fear is that the brick cleaner might eat the limestone. I tried it on some limestone left over, and while it fizzed and "smoked", it didn't appear to attack the stone. Should I use it, or does anyone have any better ideas, please? I tried a stiff wire brush on a spare bit of stone and it marked the surface. However, a stiff broom doesn't seem to shift the mortar marks, which are almost like staining rather than actual physical mortar and I've also tried a plastic kitchen scourer to little effect (don't tell the wife I put it back into the washing-up bowl, please). Many thanks for reading.

[Pablo]

Don't do it brick acid attacks Lime and calcium both of which are key components in Limestone. I made that mistake several years ago when I was starting out. Luckily it was on my own house and just a small part of it but it made a real mess. Took the whole thing down to a nasty and non-uniform blotchy grey colour. Put an expensive sealer on it which half sorted it the only other solution was to boot polish it every 2 months.Did it twice then gave up. Now when we lay it we seal both sides before its laid so any staining can be scrubbed off. Your builder is responsible for leaving you with a quality job if its stained then he should be the one fixing it not you. Apart from getting him to sort it most things will be short term and not very good solutions.

[lutonlagerlout]

you seal both sides before it laid pablo???
isnt it a little wasteful sealing the underside of flags?
IMHO get the builder back and let him put it right,in the rare event that i get mortar on stone i wash it off immediately with clean water.
incidentally i did my patio with lithofin MN stain stop today and it definately seems a quality product plus i got 2 Litres off ebay for £40
cheers LLL

[Pablo]

No point sealing just the top side of such a porous stone it just holds the salts in and stops them releasing.

[lutonlagerlout]

No point sealing just the top side of such a porous stone it just holds the salts in and stops them releasing.

eh? dont understand your logic
limestone isnt that porous,is it
cheers LLL

[Ian Mack]

Thanks, but the builder has gone to Canada to buold a house. Yes, he really has! In the meantime, there must be something that I can use to get it sorted. Any ideas? Thanks again...

[Tony McC]

Although you might think the HCl didn't attack the limestone, believe me: it did! All that fizzing and smoking - that was your limestone literally going up in smoke!

You can risk cleaning the paving with the HCl, but I'd strongly recommend you dilute it to around 5% or less and use a number of treatments rather than attempt to burn off the staining in one or two passes. If you find that the limestone is changing hue after treatment, you'll need to treat ALL of the paving, and not just the stained areas.

[mouldmaker]

I'd echo Tony's comments, and add that if you do go the acid route, soak the paving thoroughlywith water first to prevent acid soaking into the stone and doing further damage.

[Ian Mack]

Thanks, great advice, but oh gawd! Isn't some non-stone-attacking method of cleaning available? An alkali, maybe? How do the pros do it? Just wondered...

[bobhughes]

I think you should consider leaving it alone. It's a patio not an exhibit at Chelsea and the cure may well be worse than the problem. The marks that you can see will probably not be noticed by any visitor who will, of course, be tatally gobsmacked by the sheer beauty of the whole thing.

Sandstone is absorbent so anything that lands on it may well leave a mark - wine, beer, grease from the barbie, you name it and, if you have kids then never let them eat a red lolly anywhere near it.

Bob

[lutonlagerlout]

Sandstone is absorbent

i think it was limestone bob???
but bob is right in 1 respect
nothing,i repeat nothing is perfect
i can go and pick fault with things all day long,but whats the point?just winding yourself up
the mortar stain will weather off long before the stone crumbles,the professional way is not to get mortar stains on the patio i'm afraid
cheers LLL

[Rich H]

Will it not jetwash out?

[Tony McC]

Alkali doesn't really work in cleaning cement-based stains because cement, when wet, is alkaline. And when it comes to limestone, you're even more buggered because cement is...ta da...a limestone product!

[Ian Mack]

I'm told that Hg marble cement and lime film remover will do it. I've ordered a couple of bottles, will let you know how it goes. But if you know better, please tell me before the weekend!
Tony, keep the faith!

[Tony McC]

There's no data on the HG website about the composition of this product. Try it and let us know how it goes.