I seem to remember the "yard birds" using I think it was Zink Chromate as
the bare metal primer on the hull and any steel hull components. Must have
done some kind of metal etching as they were dressed in full Hazmat gear.
I know it was a dirty yellow. (Er, that was a nuke sub, BTW.)

"jalborey" wrote in message
om...
Rational(?),
thanks for your answer. I regret to say that I haven't explained
myself very well. I don't intend to sandblast again the hull after
completion (only grinding and touching up the cuting and welding areas
as required); the steel comes sandblasted and preprimed from the mill.
That's why I'm trying to ascertain the optimal thickness of a primer
coat which I intend to use as the first layer of the paint scheme, as
well as for protection during the building process (I'm going to build
outdoors, but in a dry climate). As the main protective coat I will
use epoxy tar. As the top, cosmetic coat, I intend to follow the
advise of the epoxy tar provider.
The steel provider -which is a mill working for the naval industry,
and not used to the somewhat different requirements of small craft--
serves the plate preprimed with a wide range of thicknesses for the
primer coat, and that's where my doubts arise from. May too thick a
primer coat prevent a correct mechanical grip between the preprimed
steel and the following coat?
I've contacted a couple of coating industries in my area, but they
haven't give me a totally satisfactory answer. I've send my question
via email to other paint providers, but still to no avail.
Thanks again,
Jesús



I am not quite sure of what your up to here.

Primer is Primer - as in its there to save you doing it.
But I don't know the steps they followed - did they degrease, then do
an acid etch - prime and bake in on - Maybe the stuff is quite hot
shot especially as its zinc loaded.

You can buy steel with various pre coated surfaces depending on your
situation - Are you building this thing outdoors, is rust a problem?

But you have an alternative Paint system worked out, and your going
to sand blast it anyway ?

As for paint thickness, if its a hard paint - less is best unless its
a self cleaning paint, (sheds its outer surface), soft paints are
better a little thicker - they squash up more on impact -
The hard paints chip, especially on edges - and if has a hard surface
underneath - also it cracks as stars
It depends on the resins and the fillers, type amounts etc.
But it depends on the type of paint some more flexible than others.
Which depends on its working environment - its always a trade off -$$$
come into it too.

But it seems your only going to sandblast it off anyway.
While it may be easier to sandblast of the rust - if its only slight,
this gives it a key at the same time - But it seems you need to do
more home work on this.- They should have more specs on this as to
what they have done and the coatings you can go over it with.
You need to talk with the technical folk, not the sales staff - but
they should have hand outs.

Some steel comes coated with a sacrificial coating - but this one
seems to be a bit more elaborate.
You still left out to many points - you have to do more homework.