brick

[JeffW 14]

I did a roof today and the customer asked if I could remove this white, very hard substance from his chimney.I seen this before and said "no guarantees on that stuff coming off" ,.........and I wasn't surprised when it did'nt come off.I removed some but the bit that is remaining is seemingly indestructible.Any insight would be appreciated.Thanks for any and all responses.

[PressurePros 249]

You need to go with an acid. Safe Restore or GS Restoration are two products you could use. I don't recommend muriatic acid on brick. Burns the substrate unless you are very careful.