On Sun, 12 Jun 2011 14:16:30 -0400, Home Guy wrote:

Steve B wrote:

From the looks of it, it has been on there for quite a while. What
is the best way to get that off?

Acid will remove hardened concrete from lots of different surfaces.

I remove concrete residue from ABS plastic textured form liners (4 ft by
10 ft) by spraying concentrated sulphuric acid on them using an ordinary
hand-held spray bottle. This is the suphuric acid that's sold by the
gallon in stores like home depot, labelled as muriatic acid (I think
it's used for swimming pool maintainence).


Just for clarity: muriatic acid is another name for hydrochloric acid
(HCl), NOT sulphuric acid (H2SO4):

http://en.wikipedia.org/wiki/Muriatic_acid

HCL is not nearly as strong as sulphuric acid, and is much safer to
use. Sulphuric acid is way more damaging and dangerous; it'll
dissolve skin or mucus menbranes (or metal, or even rock) in a flash.

I pretty much have to wear a mask and rubber gloves while I'm doing that
- the fumes will really mess up your nose even if you're doing it
outside.

-Zz