How to clean this concrete sill.

Bendy_House

Tee-hee, I'm not planning to go anywhere that far!

Most of the paint is perfectly sound, but I'll make sure all loose bits are tackled. It's not a 'forever' job, and they know this. Just a 5+ year put-off.

twopenny

Sills as per your other thread

I would go ahead and patch. I've done it sucessfully and invisibily which is satisfying. It lasted years invisible until my buyers knocked it down to extend in fact.

Eldi_Dos

The old fashioned way to improve the appearance of the cill would be to scrub down with scrubbing brush and soapy water then apply pumice with some clean water, not seen anyone do it for years though.

Bendy_House

D'oh! 2'penny suggested a pressure washer! Yipppeee!

stuart45

Cleaning of Cast Stone (proctercaststone.co.uk)
Go easy with it Bendy.

Bendy_House

Update. Cleaned three sills today - took less than 5 minutes with a pressure-washer.

Thanks for the idea, 2'penny, and also for the warning, Stuart. I kept the nozzle a good distance, and stopped short of blasting it 100% clean - just enough to shift the obvious black stains. But it looked very good when dry. 

I could, tho', feel a bit of extra roughness to the surface where I went a bit closer where there was stubborn algae, so take care, folks...

twopenny

Did you do the slabs too?

Yes, the roughness may mean the algae will get a grip there again - but it's going to take a long time. I wonder if it's possible to seal them? I seem to remember something about that.

JGB1955

Why did you want to clean it?    It was doing it's job... now you've removed some of it... 

stuart45

A good sealer for masonry is a mix of linseed oil and turps. You can buy expensive modern sealers, but they are based on the old school mix.

Bendy_House

Did I do the slabs too?!!! You're worse than my mum-in-law!

Yes, I did wonder about the roughness making restaining more likely, but this was probably the first time they were cleaned in 20 years, so hopefully they're good for a while yet...

I did also wonder about sealing them - there are many products out there, and they do work. However, they also darken the stone as if they were wet, and they look much nicer in the fresh bare finish.

All good for the moment