Hi,

Last night I tried to clean fireplace but had little luck. I mixed muriatic
acid with water 1:10 and sprayed brick inside fireplace, then waited about
20-30min and then brushed it with metallic brush. In same places I was able
to brush off black stuff easily, but where wall was really black this did
not help a bit.I read that muriatic acid is very good for this type of
cleanning, but probably I did something wrong.

Anyone else could point me what else helps in cleanning this?

Thanks

Use it full strengh, Why dilute it, its already diluted when you get it
If Muriatic doesnt work Sherwin Williams sells Detrich Chemicals, they
are brick and stone acid cleaning specialists and have products to
clean any stone, any building.
Hook up a few fans to get the air out fast , Muriatic burns the lungs
and fumes, also get a cartrige respirator for fumes.