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914World.com _ 914World Garage _ Powder Coating Question

Posted by: AndrewBlyholder Jan 4 2005, 07:00 PM

Was thinking of having some trailing arms powder coated. Got two estimates from local shops. Cheaper one claimed that they didn't need to put a primer coat on before the finish coat as it wasn't necessary, the finish coat adheres well enough by itself. More expensive shop claimed that an epoxy or polyurethane primer was absolutely necessary. Any advice from the past experience out there?

Thanks,

Andrew B.

Posted by: rhilgers Jan 4 2005, 07:08 PM

Primer is not required. Each shop has their own way of doing things...their way works for them.

Trailing arms are not the best thing to powdercoat. Powdercoat chips differently than paint and they will certainly get hit.
Powdercoat tends to flake off with a bit of rust under it. Primer will help with that but I would just paint them.

-Rich Hilgersom

Posted by: Lawrence Jan 4 2005, 07:28 PM

When I did my own powdercoating, I used a metal prep wash, followed by fresh water rinse. The metal prep was a minor phosphorus etcher, that also prevented flash rust.

I've never heard of a urethane primer under powdercoat. I would think that anything on the surface would cause the powder not to stick properly. That doesn't mean that there isn't a primer for that, but I've never heard of it.

Oh, and I plan to powdercoat my trailing arms, too. Smoke chrome with a clearcoat.

-Lawrence

Posted by: Air_Cooled_Nut Jan 4 2005, 07:36 PM

QUOTE (rhilgers @ Jan 4 2005, 05:08 PM)
...Powdercoat tends to flake off with a bit of rust under it...

As does ANY paint IPB Image Powder coated parts are generally blasted or chemically cleaned.

Do it and never worry about it again. The stuff is much tougher than paint and even when chipped it will greatly slow down rust whereas paint will let rust creep under. I know it stands up to heat and gas/oil very well as my engine cooling tin and fuel pump are coated IPB Image

Posted by: Engman Jan 4 2005, 07:42 PM

We ecoat and have powdercoated a lot of parts at work. We have an e coat system and sub out the powdercoat.

The most important step in any paint operation is to clean the parts. Powder or primer does not adhere well to parts that are not clean. As memtioned above any rust is a bad thing.

You can do with or without primer. If primer is used you need to check that it will be compatible with the powder coat.

Chipping is an issue with powder coating. Powder does chip if struck with the right force and angle. I really do not think chipping on the trailing arms is a huge issue unless you are on a lot of dirt roads.

YMMV

M

Posted by: Brett W Jan 4 2005, 07:45 PM

Lawrence, what is this metal wash you speak of? I need something to coat my chassis in as after I get it sandblasted. I have to be able to weld over it though. May just have to leave it bare and then come in and blast it again when I am finished.

Posted by: Lawrence Jan 4 2005, 08:10 PM

Brett,

Something like Skyco Ospho (sold at Ace Hardware), MetalReady (by POR-15 or Eastwood for under their flavor of rust treatment paint), or something like that. They're all spray-on, rinse off.

http://www.columbiacoatings.com/ sells a product, but I think that Skyco Ospho is cheaper, and comes in gallons.

Mark is dead on about preparation. But flash-rust and microrust is something that can be killed with one of these products.

-Lawrence

Posted by: jkeyzer Jan 4 2005, 10:00 PM

Jasco Metal Etch?

Posted by: AndrewBlyholder Jan 6 2005, 01:46 PM

Thanks for the primer advice guys. I'm thinking now to just go with the cheaper guy without primer. Both shops were sand plasting the parts to clean them throughly.

My 2 cents on the metal etchers: All these products are generally just phosphoric acid. Check the ingredients list and that's probably what you'll find. Strong versions are also commonly marketed as rust-convertors. The phosphoric acid changes the reddish iron oxide rust to iron phosphate, with a black apprearance. The iron phosphate supposedly is much more tightly bonded to the base metal and won't flake off and acts as a barrier to further oxygen penetration and further rusting. That's the theory anyway. I've used it a lot on various 914 chassis areas that I've stripped and repainted but didn't have the time or energy to grind down to bare, clean metal. Haven't had any problems with subsequent rust breaking out, but I'm located in California, so the climate is not as punishing.

Andrew

Posted by: J P Stein Jan 6 2005, 03:55 PM

If you run sticky tires (as I assume Andrew does), rock chips are a major issue.
I just dug out rocks up to one inch on a side out of my rockers.
My formerly pretty swing arms are well blasted at the pivot area. The etch primer under the top coat is holding up well, tho. A before pic...

Attached thumbnail(s)

Posted by: Randal Jan 6 2005, 04:17 PM

QUOTE
Was thinking of having some trailing arms powder coated

Now Andrew, what we really want you to do is undercoat that entire car with about 1/2" of lead. Maybe then we can try to keep up with you. IPB Image

Posted by: AndrewBlyholder Jan 6 2005, 04:52 PM

Sorry Randall, this is all for my street car, not the race car. Lee philosophy on paint and aeshethics is that it just adds weight (Lee is the car owner, I'm just the chauffeur.) So he cringed when I sprayed blue paint on the formerly primer finish hood last year.

I want to get my street 914 reliable enough to take on ski trips to Tahoe. I did two trips last year with no problems, however all the typical dark brown, oiled surfaces on the underside and suspension turned a bright orange as the road salt activited all the uncoated surfaces to start rusting! So I'm on a campaign now to repaint or recoat in some wayall the underside surfaces. I'm preferring powder coating as I think it will be much more durable in the long run than conventional paints.

Andrew

Posted by: Randal Jan 6 2005, 05:33 PM

Oh that car!

If you really want to make it clean underneath and protect it, then repaint everything with the Undercarriage POR 15 stuff. It wears like iron and is pretty easy to apply. Of course preparation is 90% of the effort.

The only “but” is that whatever POR 15 goes on - it will stay on - including you, so be careful.

Maybe you can borrow Britain’s rotisserie for a day; that would be the trick - and give him incentive to get his 912 off…..

Posted by: Gint Jan 6 2005, 10:27 PM

QUOTE (J P Stein Posted on Jan 6 2005 @ 02:55 PM)
A before pic...

After pics please......