Paving slabs going orange in the shade.

[Fluffycloudland77]

Our house has a sort of vestibule which is open, the paving slabs by the front door have gone orange. I’ve tried oxy bleach but it’s still there.

Do I need to use acids on it? It looks so dirty.

Pressure washer? It will remove any film and algae (and is the most satisfying form of cleaning )

I tried Wet&Forget on mine , it did The Square Root of Diddly Squat .

I don’t think it’s algae. I’ve put it down to that area never getting proper sun.

it can also be iron salts, possibly from the sand they were made of, more rarely from iron in the soil or perhaps scrap buried underneath, or dissolved in the water that's passed through iron pipes.

If that's what it is, I don't think you can remove it. Acid will remove iron stains but also degrades concrete.

I suppose it's not cat pee?

No the cat doesn’t wee there. He uses the back lawn and rakes it over with his paw.

I do re sand them every year. Kiln dried though.

you mean they're wood? I thought you meant concrete slabs.

Pine and similar tend to go orange, I believe due to the oil content oxidising.

Re-sand = fill the gaps in with sand, the builder didn’t concrete the slabs in.

could it be stains off the sand?

It’s possible isn’t it..

Citric acid might shift it, lemon juice gets ferric chloride out of clothes.

orange stains from sand are often called "iron salts." I don't know if that is chemically correct. If you handle it damp it leaves orange stain on your hands and clothes, which don't seem to wash out.

If a pile of sand is left on clean concrete for a long time, it sometimes leaves a permanent rusty stain. I don't know if there is a way to get rid of it. Acids erode the surface of concrete.

You can buy silver sand, it is sometimes used for a very white render, with white cement.