Path Stains.

[conny]

Posted this in garden section but thought I'd have more chance of a response if I mentioned it on here as well.

Have recently tried to pressure wash the path clean but cannot get rid of these stains.
Can anyone tell me what they are and, more importantly, how to get rid of them?

 

[joe-90]

Two choices. Acidic brick cleaner or caustic soda. If neither work then nothing will work.

 

[conny]

Thanks Joe.

 

[snico]

They are lichens, like an alge but they can root into the paving

Sodium Hypochlorite will remove them, but its a long process as the acid needs to work into the structure of the paving, and a good brush with a stiff brush will help.

 

[joe-90]

Sodium hypochlorite is bleach and is an alkali.

 

[freddiemercurystwin]

Why are so many dopes posting their building issues in GD these days? Muppets!

 

[joe-90]

They know where they can find me.

 

[snico]

Sodium hypochlorite is bleach and is an alkali.

Sodium Hypochlorite is not bleach, bleach contains about 5% Hypo. Its a base

 

[r896neo]

use sodium hypochlorite as stated diliuted 2:1
2 water to 1 part chemical.

Pre-wet the slabs then water it on with a watering can and agitate it with a stiff brush. Leave it to sit for 20 mins and keep it damp and brush it every 10 mins.

Then wash off. Be careful of the run off though as it will kill grass at that dilution. heavily water the grass or plants before and after.

 

[jay679]

I don't know why people are so obsessed with keeping things immaculate. To me, those slabs just look naturally weathered and perfectly ok. Sorry OP, don't want to sound like I'm having a go.