I too have a brick cleaning problem. I pulled off a 37 yer growth of grapevines from my brick fireplace chimney. Remaining is a residue of light brown colored material My first thought was it might be calcium leeched out from the mortar but it doesn't respond to muriatic acid. It is obviously a residue from the vines, but it is hard as heck. I swear, it must be petrified wood! But most likely it is a stain from the vines and has penetrated down into the brick. It doesn't come off with any cleaners. The only way I have been able to remove it is by wire brushing with a wire brush attachment to my electric drill. This removes the stain along with some of the brick. That's an awful lot of wire brushing to do! Might there be a stain remover to easily remove it? I will next try some turpentine, paint remover, etc.

I used paint remover & Diedrich 101 to clean my brick & had awnings, liquid nails, vines, & paint sloppings all over it.

It is not recommended for a DIY, due to strong hydrofluoric acid content.

http://www.diedrichtechnologies.com/page4.html

If you guys go to your local brick supplier, they will have a similar product.

FYI, a pressure washer is needed after spraying on the solution.

Try Krud Kutter, http://www.krudkutter.com/originalkk.html

It is amazing what it will remove. Can be purchased at Wal-mart, Sherwin-Williams, or your local paint store.