It’s a bit hard to tell what the discolouration is but a good place to start with this would besoda ash – other names are washing soda and sodium carbonate. The best place to get this from are pool shops or the pool chemical section at Bunnings.
Or better still, try a chemical supplier and see if you can buy a 20 kg bag of it – it shouldn’t cost more than about two dollars per kilogram.
Carry a bucket of water with you, and then just use the soda ash as a powder cleaner. So wet your sponge, swab it in the soda ash to pick up some crystals, and then just rub it over the area that is covered with the grime. Then just wash it off afterwards.
After you have finished it will leave a light dusting of the white soda ash on the stone, but because it’s white on white you won’t notice it. In any case, that should discourage further growth of what appears to be mould.
An alternative approach would be bleach (depending on how the soda ash goes). You want about a 4% solution. This is what is normally in the stuff you buy from Bunnings (White King for example). Don’t waste your money on Exit Mould – all it is, is bleach with some fragrance added.
If you’re lucky you might find some 12% bleach – if you do just water it down one in three, and then buy a generic spray bottle to use it with. It might be worth your while to buy one of the 5 L or 8 L garden sprayers from Bunnings. Bleach takes a little while to work – so spray it on and wait a few minutes – the coulr should gradually fade.
Certainly you will need to use the bleach to get into the delicate places where you can’t get to with the soda ash.
On the other hand, if the brown stains on top are rust, you’ll need citric acid.
Although the bleach will remove the colour, it will not actually remove the organic material from the surface, and it will eventually reappear. Hence the use of soda ash.
I’ll be talking more about soda ash on my radio show today.
Continue at: https://www.drchemical.com.au/cleaning-gravestones
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