Oxaltic acid works fairly well. It is mainly used for removing calcium and
lime stain and work also on removing rust.
It is sold under an household name of FLR (in Canada). In boat store Davis
is selling a product called FSR (fibreglass Stain Remover). It comes is a
gell form its little pricier and works well. I have used it for years to
clean the bottom of the water line on my boat after haul out to remove
algae's stains
Using this product for many years I have learned that it work best a about
70F. I have noticed that it after several usages it augments
(increases) the porosity of gel coat. This in return has for effect to make
the surfaces more prone to stains. Using diluted muriatic or oxaltic acid
on freshly painted deck with Imron or its equivalent may increase the
porosity and make it more prone to stains?
That why for a small job I first use strong tooth past and if this does not
work then I use FSR (oxaltic acid gel).

"Mark Borgerson" mborgerson.at.comcast.net wrote in message
. net...
In article ,
says...
I have use diluted muriatic acid on concrete and gel coat.
However, I do not know the result if you use it on emron finish. BTW is
this finish also known as DuPontT Imron® Polyurethane Enamel? The best
thing would be to experiment with diluted muriatic acid before using it.
The last time I have use diluted muriatic acid was to remove barnacles.
The
timing was crucial. Soon as you are finish removing the rust or
barnacles
you have to rinse the surface immediately with lots of water. Failing to
immediately rinse the surface with lots of water could deteriorate the
surface finish and fibreglass.

wrote in message
oups.com...
I used to store my boat near a RR trestle and every spring would have
to remove freckles from the deck caused by minute steel molecules. We
all used dilute muriatic acid very carefully.


On our last charter, the boat came equipped with a fiberglass
cleaner that contained oxalic acid. That acid does a good
job of dissolving iron oxide--by forming oxalate complexes,
I think. It worked wonders on the rust streaks around the
anchor stowage and windlass. The only remaining streaks were
in areas where it looked like someone had waxed over the
rust streaks.

Google "fiberglass cleaner oxalic acid" for more than
you wanted to know.


Mark Borgerson