Deep black algae in patio slabs.

[Ariesburn]

Hi,

Anyone know how to get dark black algae/ spots out of patio slabs? I've jet washed it and used a chemical that's pet and child friendly but it's not budging?

Anyone?

@Ariesburn The best products are not pet friendly whilst it is working, it just requires keeping pets off it and then a lot of rinsing off. The black spots are usually lichen, you can get both black and white spots. I have these on my patio and treat it myself. My patio is Indian sandstone in Kandla grey. I sat out in my garden whilst it was working because I don't have pets but some cats may come into the garden so I was there to scare them off.

Sodium Hypochlorite is the cleaning product, also known as hypo, a million videos on Youtube showing you the effectiveness. For me I have a path down the side of my house so I did a small test area on one slab because my patio is large and I wanted to know if I needed to do it in two sessions. Best to do it soon because you want an overcast day and need to keep the patio wet whilst the hypo works. It is basically a bleach but stronger than a household bleach.

Here is a video of a chap doing his patio.

V

There are also other professional ones too. References to "soft wash" is a surfactant cleaner, this chap says "soapy Hypo" which is a mixture of both the soft wash and the hypo. You can buy hypo on Amazon.

Please google what your patio is made from before proceeding and if you do proceed then please do a single test slab to make sure it isn't changing the colour of the sandstone. I believe some is more liable to colour change.

Thank you!!! I will try this solution 😊