Your favorite priming process??

[mhorowit]

For portions of the a/c anatomy that will receive fabric cement, I know we need to use an epoxy that won't be affected by the cement, hence no ZC for those areas.

For priming of other steel parts, what process do you use? The same, which I assume is an etch-prime followed by a 2 part epoxy?

Or do you use a less expensive process? if so, care to provide a brand name?

- Mike

[jgerard]

Re: Your favorite priming process??

I like a polyurethane over everything before starting fabric work. Etch prime, sealing prime, paint, cover.

Jason
N43643

[N96337]

Re: Your favorite priming process??

Mike, prep will be explained in the covering manual of whatever system you use. It must be followed. I'm a PolyFiber kinda guy so I go with PolyFiber epoxy primer on everything, then a polyurethane to seal it all. As an ex-paint tech-rep, I always seal with polyurethane, unless the manual calls for something different, or it's something like a leading/trailing edge, or something like that. I just use the epoxy there, as it's going to be sealed with the fabric, then a polyurethane topcoat.
John H.

[mhorowit]

Re: Your favorite priming process??

Folks - I'm asking about parts that won't contact fabric i.e. a bell crank or an aileron bracket - Mike

[jgerard]

Re: Your favorite priming process??

Everything steel should be painted up through a polyurethane. Things like wing ribs I am satisfied with alodine and zinc chromate.

Jason
N43643

[Ragwing nut]

Re: Your favorite priming process??

Sandblast and Stits epoxy prime everything. If repairs are needed and it will be a while I etch prime and then epoxy after repairs are finished. I only polyurethane what will be seen when finished.

Mike

[mhorowit]

Re: Your favorite priming process??

I"ve seen the phrase "etch prime" - what does it mean? - Mike

[Ragwing nut]

Re: Your favorite priming process??

"etch" prime refers to a particular primer that contains phosphuric acid. The acid attacks the steel and chemically treats the metal surface in preperation to accept paint. It does the same thing for steel as alodine does for aluminum.

Mike

[mhorowit]

Re: Your favorite priming process??

"etch" prime refers to a particular primer that contains phosphuric acid. The acid attacks the steel and chemically treats the metal surface in preperation to accept paint. It does the same thing for steel as alodine does for aluminum.

Mike

dealing with 4130: when would I use an 'etch primer' vice a regular primer?
Are you saying you need to etch prior to priming and that some primers (etchprimers) do that job in one step? you said 'treats surface in prep. to accept paint' (didn't say primer) so that confuses me- Mike

[jgerard]

Re: Your favorite priming process??

2 ways to get paint to stick. Mechanical etching, or Chemical etching. Sand blasting would be one way to mechanically etch steel. Scotchbrite pad on for aluminum does the same thing. After a surface has been mechanically etched and cleaned with the proper solvent to remove any remaining oils it is now ready for primer. Most regular primers do not seal the base material from the environment but rather provide a surface that paint will stick to better than the base material. Zinc rich primers provide extra corrosion resistance. If you do not plan on top-coating over the primer paint make sure it is a primer sealer type of paint. I prefer using a zinc rich etch primer on steel regardless of whether or not it has been mechanically etched. Epoxy primers to not stick any better to steel than regular primers they are good tough primers and some of them are even primer sealers. I have been working on a Helio Courier where the whole internal steel cage was repaired, blasted and Epoxy primed and the paint is flaking off every where. IT was painted with BMS 10-11 which is a Boeing epoxy paint. Tough as nails, but sure is hard to get to stick to metal. What ever primer/paint you want to use make sure and follow the manufactures directions.

I am from the NW and if you don't properly prime steel it will rust fast. So I have found out what works and what doesn't. There are so many types of regular (non etch) primers that have very poor adhesion to steel that I don't even bother with them anymore. No reason not to use a GOOD self etching primer. If the surface has been mechanically etched and you use a self etching primer its like doubling the bond of the primer to the base material. Getting other paints to stick to primers is not that hard. I have areas of small rust holes on the top side of some of my lower fuselage tubes and nothing on the bottom side. I am guessing this is because the old primer cracked and let moisture in under the paint.

My favorite etch primer is Duponts Variprime. About $80 for a 1/2 gallon kit. See attached doc.

Jason
N43643

[mhorowit]

Re: Your favorite priming process??

Thank you thank you thank you.
Great info; much appreciated - Mike