Patio Black Spot Preventer - For all Stone Types - Controls and Prevents Reinfestation after Removal - Suitable for Terraces and Pathways - Removes Red and Green Stains From Algae - 2.5 L

It works ! Great stuff.

Prevents black spot on patio when used annually. Works every year.

This product worked perfectly, does exactly what it says on the label. My slabs looked really bad but now look like new. Really pleased how good they look. I needed to go over them a couple of times but definitely worth it. I have also brought the preserver and will use before winter

The product must be reapplied each year, so is expensive but worth it to keep the patio looking new

I've used this for many years and it does exactly what it says