The surface needs to be very clean, and not oxidized. The reliable
method of prepping the galvanizing is to etch it before applying
primer, and applying paint to the primer coat (not to the galvanizing).
Etching is accomplished by wetting the surface with a diluted
phosphoric acid solution. The etching agent is available at paint and
refinishing product suppliers, and is commonly referred to as metal
prep or etchant. It's other uses are for etching new metal parts,
including mild steel, aluminum or stainless steel, to prepare the
surfaces for primer.
Alternative methods would be to use other products such as etching
primer, or zinc chromate primer. These products also require very clean
Get the right primer and paint. Suggest talking to an industrial paint
Auto paints for galvanized steel are also very good, but these pieces
may be too large for that to be practical.
Etching the metal before the primer is necessary. People often leave
galvanized surfaces unpainted for a year, and let the weather do the
prep. Auto body shops cant wait that long and so use a special etching
The phosphoric acid, "Metal Prep" is very effective, but be sure NOT to
leave it on the galvanized sheet too long. It will completely remove the
galvanizing, given enough time, and enough time is not very long for thin
electrogalvanizing. Try out a small sample first.
The traditional method is allow it to get a year old or to acid
etch. I picked up a can of latex galvanized primer expecting to
be disappointed and able to chalk up another latex product that
did not work well with steel.
I was quite pleased and surprised that it did an excellent job on
some sheetmetal pipe guards.
Keep the whole world singing. . . .
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.