Fiberglass over Stainless steel panels

[mik lenoir]

Hello boat experts
Need to improve my understanding on applying epoxy/glassfiber over bare metal; in this case 316 S/S sandblasted to roughen for better bond.Sheets are bend and have 1/2" deep flanges welded from other side.
The coating is needed to fill, smooth and fair water exposed surface.Must also support antifouling paints.
I am concerned about permanence of such coating, particular any osmotic penetration of seawater through layers.
Would rather prefer epoxy over polyester (osmosis?).
Could you please comment on this with your expertise and knowledge.
Thanks mik

[gonzo]

If you use thickened epoxy to fill and then 2-3 coats of pure epoxy over it there shouldn't be any problem.

[yokebutt]

Mik, I would use the method recommended by Gougeon Brothers. (the WEST system manufacturer) Sand surface with coarse sandpaper to bright, apply a coat of neat epoxy, then sand that into the surface while still wet, that way the metal is never exposed to air between getting scratched and becoming coated with epoxy. After that you can laminate away to your heart's content.

Yoke.

[mik lenoir]

Hello gonzo and yokebutt;
thanks for comments
but still have concern and questions.
To benefit from S/S in marine environmt. the surface needs to be passivated
or oxidized to stand up to corrosion, correct?

If let say sandblasting or rough sanding is applied, then this protective layer is being removed. Of course it seems logical to roughen surface to better bond any coating to it. To passivate the procedure of a certain acidwash and rinse has to take place.

If someone would roughen surface while applying the epoxy (not a pretty picture) the surface stays active and locked in that condition, until coating is damaged later on and corrosion(local and pinpoint?) can take hold.

Stainless needs oxygen to build and even regenerate the protective passive layer but someone likes to fair things up and by doing prevent this process.
Sounds like a dilemma. So what does the real world do?And how is longtime exposure affecting the surface of S/S?
Any application experiences?

This gets a bit to deep here but that why forums are so helpful.
Please let your comments flow!
Thank you mik

[D'ARTOIS]

Itis exactly as Gonzo and Yokebutt are trying to tell you. After the metal has been impregnated with epoxy, it is very close to inert. If you follow Gonzo's instructions, and those of Yokebutt the epoxy will make an impenetrable layer on the stainless steel, if done so, it will keep for a long, long time.

[Skippy]

Even if there is penetration, I'm not sure I would worry about it any more so than with paint. My impression is that the effect of water is faster than that of air, but not much different, so the oxide layer will form on contact with the oxygen in the water. Not that you want corrosion, just that it won't disintegrate any faster than it would with a bad paint job.

[chandler]

Never heard of a stainless steel hull. Must be pretty expensive..

[cyclops]

The Pirates are going to want your boat real bad.

[yokebutt]

I've never really heard a full explanation of why stainless corrodes without oxygen, by definition it cannot oxidize under those circumstances. However, chloride has many qualities in common with oxygen, and in seawater there is plenty of that around, albeit in a placid ionized state. Perhaps we could entice someone with a metallurgical background to clarify.

[mik lenoir]

I used 304 and 316 in brackisch water partially immersed in bottom mud.
The part in the mud and under neath where oysters etc attached was heavily pitted while the part where salty water had access was stained and also corroded, but not as badly.
304 of course suffered much more material loss.
S/S pipeclamps showed the worst corrosion under the clamp part and under the overlap . But using electrical tape to cover parts of S/S surface was effective .
It seems the organic influences of whatever growth on it has a bad influence
on longtime performance of S/S in marine environmt.

[chandler]

I'm not a mettalurgist [sp?] but from what I understand, ss needs air to form it's protective coating.