Question and answers on Stucco and Plastering-- July, 2011
Rust stains
How
do
I get rust stains off of
stucco ?
Oxygenated bleach works, somewhat. Years ago, I saw
someone remove rust stains with a solution that worked like magic.
After investigating, I found out that the material used was
oxygenated bleach. The oxygenated
bleach from years ago isn't made anymore, because it is a toxic
chemical.
I bought some of the modern oxygenated bleach
online. These days,it is made from grapefruit seeds. I tried some and
it just doesn't work like the old stuff, but it will take most of the
stain off.
Stopping the cause of the stain is probably as important as the removal.
One problem we have had is iron oxide in the finish coat sand. I think
I deleted the pictures the guy from Florida sent
me. If I can find them, I'll post them, because this looks like what is
going on.
We used sandblasting sand from New Jersey on a couple of our jobs. What
probably happened was that particles of
steel from the crushing process got into the sand. About 3 weeks
later, little rust spots appeared about every three
feet or so. We did a big addition with sort of an orange stucco, and it
really didn't look bad. We did a greenish color
stucco that did look bad,so I coated the whole wall over again.
A woman from Philadelphia wrote about stains under her windows. These
were apparently caused by galvanized stop,
or casing beads, used on the stucco application. These galvanized metal
trims rust and rot, so we quit using them.
They make a zinc coated stop, but they are not only expensive, but are
so flimsy that I doubt they offer any reinforcement
value.
This is why we started just butting the stucco up to the window without
using metal trim years ago, like they do in
California.
Another source of rust stains is the practice of putting mortar on
paper thin and rust from the nails on the lath
bleed through. The standard thickness for cement stucco is 3/4". The
unfair competition sometimes gets by
with a 1/4" or so. Usually half priced work is less than half the
quality.