Cleaning/restoring blackened sills

[dwolff4]

Hi there,

I live in a terraced house from the early 1900's. I'm looking to clean or restore the blackened sandstone sills underneath and above the windows. Our neighbours have painted, but I would rather try and get the surface back to a natural colour. You can see how it currently looks in my attached image.

Untitled

• dwolff4
• 14 Apr 2009
• 2

I've tried pouring on some strong household bleach, but that didn't work very well. I also purchased a wire brush attachment for my drill, that probably would have eventually got there, but was just way too slow (less than a square foot got less than acceptably clean in an hour of brushing ).

Does anyone know of any methods or products that will get me back to my original sandstone colour?

Thanks

dw

 

[Burnerman]

Other than brick etching chemicals, which I don't think would be acceptable here, you can use a diamond grinding cup, suitable for 115mm angle grinders which will quickly whisk its way through stone. Takes a little practice to avoid swirl marks though.....check out Screwfix Erbauer ones, part number 53986, £27 each.

 

[dwolff4]

It worked a treat! You were right about the swirl marks, but I improved as I went. Doesn't really matter as it will be mostly seen from relatively far away.

I do have a follow up question, do I need to treat the exposed stone with anything to 'seal' or something? Or something that will make it resistant to re-staining?

Thanks,

d

 

[Burnerman]

Pleased that worked ok! I don't think you really need to add any other treatment as the lack of coal fire pollution today means that your sills should remain clean for much longer...however, a solution such as Thompson's water or block paving seal (Screwfix 82281 or 22319) is excellent for resisting water penetration and other airborne dirt.
Cheers John

 

[jameshere]

A bit late answering, but I've just joined, however, for future reference, why not try a high pressure washer.

I have a fairly small pressure washer, we have some old red sandstone boulders in the garden, their original colour is a sort of fairly bright reddish pink, but these had been weathered and stained until they were almost black, and they had green algae on them, the pressure washer brought them back to their original colour.

In fact, you have to be really careful, because sandstone is so soft, and pressure washers are so powerful, that if the nozzle is held too close to the sandstone, and or, for too long, it will actually cut gouges into the sandstone.

Of course, in your case the main problem would be, or rather, would have been, gaining SAFE access, but perhaps the washer lance might have been long enough to reach from the window with the assistance of someone to hold you, or perhaps extension lances might be available, or ladder access might have been possible.

Those washers will also clean old coping stones on top of walls, I used mine on some blackened granite copings, and it brought them back to their original light grey colour.

They will also bring old fence panels back to the original wood, ready for recoating, but again of course, you have to use the washer with care, or else it will chew through the wood.

I imagine that they would also strip old paint from brickwork, and they might even clean up old stained brickwork.

I agree with the chap who says that you could coat your sandstone with a sealant, with todays cleaner air, they might not blacken so quickly, but with sandstone being so porous, algae growth might be a problem, so I would look for a sealant that contains an algae inhibitor, or paint them with a solution of algicidal liquid.