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gsrokmix 01-25-2004 12:33 AM

Primer before powder coating?
Hi guys,

My local powder coater says that they use a zinc primer on all parts before they powder coat. I have been blasting parts at home over the last couple of weekends. I'm going to powder coat all brackets, core support, rear end ect.. Even though I've been storing the bare blasted parts inside the house in a spare bedroom they are still starting to rust a little. Is there a primer (like the Zinc primer Eastwood sells) that I can use at home to seal my blasted parts? I want to take a truck load to the PC'ers at once to save some $$$.

Thanks as always!


adtkart 01-25-2004 06:55 AM

I hope someone has the answer for this. I didn't realize that they primered parts before powdercoating them.

Twin_Turbo 01-25-2004 06:19 PM

don't use zinc primer. The best treatment is zinc phosphate but that is done in a chemical washing/cleaning setup and you won't have it at home. Just clean the part thoroughly and apply the powder. The rougher you blast it the better.

daimon1054 01-25-2004 11:32 PM

Look around for a rust preventative spray, a friend of mine sell some that can be washed off then painted later. Also the powder shop should clean and pre bake your part so call them and ask if coating the parts with a light coat of oil or what ever they recomend.

Go to
They have a product called MD50 that I put on my 5th wheel hitch because it was always rusting. I put it on and it stayes outside and it has not rusted in a year now. It can be washed off and the part painted.

302 Z28 01-26-2004 04:56 AM

As mentioned, a pre-bake is used by most powder coating operations to remove, or bake off all traces of oil. I have not heard of any using a primer.

Vince 01-26-2004 07:40 AM

Since the whole idea of powder coating is to have a pristine chemically and mechanically clean sand blasted white metal surface on which to melt the plastic powder, I can't imagine what kind of primer would enhance the process. I have my pickup frame, running gear, fender wells, and a bunch of other parts down at my 'coaters right now. I'll ask him if he knows anything about that. He has pretty good credentials, does a ton of oil field and refinery work such as the 6,000psi refinery heat exchanger enclosures he was doing when I dropped off my frame.

bullheimer 01-26-2004 05:09 PM

i thought it only went on bare metal as well. in either case, i would NOT put any primer on "for them". if it's the wrong kind or they dont know what it is they will sandblast it off and charge you for the sandblasting.

adtkart 01-26-2004 07:18 PM

I wouldn't be near as concerned about them charging to sand blast the part, as I would them blaming me for their work failing later.

Thom Laybourne 01-27-2004 11:53 AM

I have had several frames PCd and they want you to leave them unfinished. They tank for a good clean and it will remove rust. Better to pay attention to SMOOTHING areas. Powder Coat will level, but not fill in. Use a good Scotch Brite wheel and get it flat. I took about three months out side cleaning the frame and scotched it smooth. They tanked it and did a great job.

hr41pearl :cool:

Twin_Turbo 01-29-2004 05:02 PM

a good powdercoater will not only tank it to clean but also dip it for a zinc phosphate coating. My brother is a coating engineer and he has lots of experience with powdercoating systems and development and for a top notch result it's the best way to go. Chances are that if you deliver your parts blasted they will clean adn dip it. But, do not use anything that comes in a can.

When powdercoating galvanized parts the zinc phosphate is an absolute must. 02-03-2004 08:07 AM

I finally got hold of my powder coater and asked him about the idea of primer. He said 99.999% of the time there is no need. Some less reputable coaters avoid the expensive sandblast-to-white-metal step and dip the parts in a phosphoric acid etch solution hoping for a good bond of the melted plastic.

There are proprietary industrial plastic coatings that 'require' precoating with a phenolic epoxy plastic and final coating of the outer surface. Funny thing, California outlawed the phenolic epoxy primer and the vendor issued a product bulletin that said, "Shazam, we just discovered that the outer coating works great without the primer so keep buying our stuff!".

My guy started getting questions from new customers, "Do you metal spray before powder coating?" Strange request until he found out that some guy in northern California was doing that. Not a good idea. Although metal spray does have a VERY rough and porous surface and would bond extremely well to the plastic, it sometimes does not bond well to the base metal and flakes off. Also it would at least double the cost of the final job with no significant improvement in performance. Metal spray is old tech as far as decorative coatings go.

Finally, my guy says that for some hard to cover colors, he will 'prime' with a similar easy to cover color, then put on the final color.

For our purposes, just take your grungy parts to the coater and ask for their standard blast & coat service.

myfamiliacc 02-03-2004 03:38 PM

[color=orenge] This is all great info! :thumbup:


gsrokmix 02-05-2004 12:43 AM

Very interesting info guys! I am blasting the parts at home to save money as well as to see the real condition of things under almost 40 years of dirt and scale. I have checked with a couple of other PC'ers since my initial post and they said that they do not primer and that coating with an oil to prevent rust after blasting was ok since they were going to give the parts a bath. I am going to take a ride to a couple of these shops before I give them any parts just so I can scope them out more closely.

Thanks again!


Thom Laybourne 02-05-2004 08:09 AM

Ask them what they recommend you do to get rid of any blemishes in the frame. Will the PC smooth everything out or do you need to grind it down? I like mine smooth, so I grind them down. But they may have some new way that is less aggressive to the metal. Be interested in knowing.

hr41pearl :cool: 02-05-2004 08:41 AM

Use this stuff on the base metal like you would use bondo under a paint job for a perfect surface before powder coating. This will stand up to 1000F temperatures - the 400F that the coater use is the recommended curing temperature.

High temperature Lab Metal

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