Cleaning the flagstones

[jennG18]

Can anyone help me? I have just moved into an old house and the flags in the back yard seem to be original one but the are covered in a green colour! also the walls too, I know its a natural thing to happen but I want to clean it off! I have used a power jet to wash most of it off but there's still stubborn parts that wont come clean! I have also used washing powder, washing up liquid, bleach and Ajax and scrubbed the flags with a yard brush but this method would be no good for the walls (original stone walls) and it drives my neighbours insane! I don't know what to use to get a sparkling clean yard! any help will be greatly appreciated!

[Hamish]

I have used a concentrated solution of caustic soda (you can get it in the chemists (UK)) Take care when dissolving it it gets very hot and never add it to hot water. Wear safty glasses and was it off you skin if you get it on. It will eat through cloaths (including leather) so wash them too if you get it on. I think I used about 100g in 5L. This will kill just about anything on the stone ..... but will probably eat the stone too. It may also damage moarter on the house, I only used it on the yard flaggs. Let the solution sit on the flaggs for a few minutes before vigerously scrubbing it off and rinsing throughly. Don't get it on tarmac or the garden! The problem of growth may reoccour this will be because of damp in the area (our yard was very shelered from the sun and wind). You may need to keep cleaning regularly (or possibly apply a weed killer such as sodium perchlorate (take great care with this too, it will kill just about anything!). I would seak more advice before trying this on the house though ..... any one else any tips? All the best Hamish

[Mick]

You could try Brick Acid which is available from builders merchants and some hardware stores. I don't know if it would be more or less severe than caustic soda. I work in the restoration and duplication of old stone buildings and have been told that I could save a lot of time and effort by using it to clean up and bring out the natural colour in freshly built stonework. I haven't tried it yet but will in the future. Whatever you do, find out as much as you can from the vendor and read the instructions carefully as it is potent stuff! Good luck!