Caustic soda?

Use diluted bleach in a spray bottle. Mine were aquatic green until I sprayed them last week. It got rid of the staining that even the pressure washer wouldn't shift.

 

Caustic soda burns FC, I wouldn't risk it especially if animals walk across it after.

 

I'd stick to bleach for cleaning the patio. Caustic soda is very corrosive and needs to be used very carefully.

 

I agree with the other answers above. Caustic soda can be useful for shifting grease as in unblocking a drain when used carefully, but isn't suitable on a patio.
Good luck with the cleaning

 

I agree also, if possible stay away from caustic soda it also gives off fumes.

 

I clean mine with ordinary cheap thin household bleach, in a trug with hot water, pour over area , leave for a minute or two, scrub with stiff brush, and then power wash to remove residue, dog indoors. I get a very greasy thick layer from steel works so power washing alone is not enough.

 

Ditto...except I leave the bleach solution on for about half an hour. Seems to improve the cleaning action.

 

As others have said, best steer clear from caustic soda. The bleach is a good shout, though I use Stardrops which doesn't harm plants or grass and no bleachy smell. Pail or warm water, slosh it over area, few good squirts Stardrops, give a good going over with a stiff broom to suds, leave for half an hour, give a decent scrub with stiff broom, then slosh with warm water to clear.

GG

 

If you use caustic soda FC make sure you use gloves, eye glasses and don't sniff the fumes, i used to use it when making caustic wheat (animal feed) one slash and it will burn, if you do get some on your skin wash off straight away
We don't want you in A&E

 

29p for 2 litres

 

I just use the Smartprice thin bleach as well . I think thick and thin bleaches are the same strength . The thick is so it clings to toilet bowls etc. I put about 1 litre in a bucket off hot water with a squirt of detergent so its only 15p a bucket .