Have done as much as I can and put out a job on Mybuilder.com to try and get an expert to come and clean further and apply the seal but have had no response and I do not want to enquire around locally myself because there are a great deal of cowboys around and would not trust anyone not recommended by a reputable site. My question now is if I put the sealer on with some of the black spots still remaining can they still do harm or spread beneath the sealer or does the sealer effectively kill them (I gather they are living organisms??)
Sorry I missed your post earlier, but either bleach or ammonia are fine, they are alkaline so will not damage the surface of sandstone/limestone/marble - unlike acidic cleaners, including vinegar, which will eat away at the surface and give lichen a better toehold than before in the subsequently enlarged microscopic pores. Much imported sandstone is of poor quality I am afraid.
I use ammonia on sandstone to good effect. Once clean, I always seal afterwards with Lithofin products, they are excellent quality and you know if it says it is safe for a certain stone, it will be. You have to really flood the stone though, let it sink in and wipe of the excess, then give it at least 24 hours and repeat. The coverage is never as good as claimed so bank on using a lot more than they say you need.
Always use a PH neutral cleaner for general maintenance cleaning afterwards.
If if you can’t get all the lichen off prior to resealing and/or have damaged the surface (likely if you used vinegar and vigorously cleaned with a pressure washer) you might just have to live with it looking a bit weathered. People pay a lot more to have antiqued, aged stone so think of it that way and you will feel better!
Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
Thanks for that advice Nollie. What a nightmare I have had with this patio, I have caused more damage to it than the lichen with everything I have used. In the end cleaned it with Sodium Hypochlorite 14/15% and sealed it with Sandstone sealer from Universeal....it had very good reviews so hopefully will last. Patio looks amazingly good considering the battering I have given it when I did not know any better. It is not exactly like new but good enough for me. I am just glad it is all finished and done with. Thanks everyone for your input
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I use ammonia on sandstone to good effect. Once clean, I always seal afterwards with Lithofin products, they are excellent quality and you know if it says it is safe for a certain stone, it will be. You have to really flood the stone though, let it sink in and wipe of the excess, then give it at least 24 hours and repeat. The coverage is never as good as claimed so bank on using a lot more than they say you need.
Always use a PH neutral cleaner for general maintenance cleaning afterwards.
If if you can’t get all the lichen off prior to resealing and/or have damaged the surface (likely if you used vinegar and vigorously cleaned with a pressure washer) you might just have to live with it looking a bit weathered. People pay a lot more to have antiqued, aged stone so think of it that way and you will feel better!