On 6/12/2011 2:41 PM, Zz Yzx wrote:
On Sun, 12 Jun 2011 14:16:30 -0400, Home 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

Both acids are sold in concentrated form which is 38% for hydrochloric
and 98% for sulfuric. Both are strong acids and form the same low pH in
water. Concentrated sulfuric is a strong dehydrating agent which makes
it more dangerous to skin. Hydrochloric will evaporate but sulfuric
will not and trace acid will remain to do harm to clothing and the like.

Many people have been burned pouring water into sulfuric acid which will
boil and spurt because of the heat generated from hydration.
The dilution rule is to slowly add acid to water but never add water to
acid.

A drop of either acid in the eye can cause permanent eye damage.

We had a project using sulfuric and operators were complaining that
while their acid resistant clothing was holding up, it was degrading
their underwear. Supervisor wanted to buy them acid resistant underwear
but I said, after the underwear, there is their skin. If acid splashing
is so bad, they needed to wear acid proof (rubber or plastic) garments.