Patio cleaning

Mujie66

I have pressure washed our patio but it still has black spots. What is the best way to remove these?

djp64

The black spots are lichen that attach themselves to the slabs.  I spray ours with a 1:25 solution of BAC50 (Benzalkonium Chloride).  It  doesn't work immediately but over time kills and keeps deterring the lichen.  It's 'reactivated' when it rains so keeps working for 18 months to two years.

I did some experimental spraying last year to see if it worked and on the Indian sandstone patio the one's I sprayed are completely clear of lichen.

Debbie

Dreambox

Maybe it is mold?? Sometimes it will stay there and won't go away, had some problems with it in the past... 

TELLIT01

I've found Spear & Jackson Spray and Leave to be pretty effective.

Ajmason42

That large online company that resembles a rainforest  starting with an A sell various spray on cleaners  I've used pro klee green mold and algae remover and am impressed so I would try one of the specific black spot removers

EssexExile

Sometimes they can't be removed, it depends what they are & how long they've been there.

stragglebod

Sodium hypocholorite. As found diluted in household bleach.

tattyjacket

I've been plagued by Black Spot for a few years now, ruining the look of my patio. I've tried all sorts of things but I think I've found the answer. Cilit Bang Black Mould Remover....from all major supermarkets. 
Things I've learned. 
1) Work slowly, slab by slab. Give each slab a good spraying. Cover it over with something, especially if you have pets.
2) Best to work when the weather is cool. The fluid needs. to stay fluid for a while. If you try this on a hot, sunny day, it will evaporate too quickly and then it won't be effective.
3) Sometimes you will need to apply the spray two or three times, removing persistent marks with a pressure sprayer.
4) Afterwards, be more thorough with your regular cleaning. I used to pressure spray my patio just once in the Spring. I think I'll aim for three times a year from now on.
Phil

stragglebod

tattyjacket said:

I think I've found the answer. Cilit Bang Black Mould Remover....from all major supermarkets.

i.e. Sodium Hypochlorite in expensive packaging.