Working with epoxy primers

[TASEsq]

Hey Greg,

I?ve been using the water based Stewart systems EkoPoxy for my build - I?m building at home and it?s environmentally and physically non-toxic. The gun just cleans up with water. I acid etch on the drive and just hose it off. I used syringes to get it out of the pail, which I?ve cleaned with acetone and scotchbrite to remove any silicone.

It?s not that cheap but is hard wearing once it?s cured for a few days. I can dimple after 12 hours.

The only downside is the cost - at least shipping from the us is non DG. The last purchase was 2 quart cans which I mixed together in a plastic pail. Total cost delivered was $308 AUD (paint 200 ish and shipping 100 ish).

I searched high and low for a primer solution here in Aus, but couldn?t come up with anything that was not completely toxic or impossible to clean up.

I did come across a rattle can the other day which I am going to try - it?s called Norglass no rust all surface primer - they answered via email very promptly and advised their primer is not hygroscopic and doesn?t need to be topcoated. So I?m going to try it out and potentially use it for small jobs and on steel (you can?t use the ekopoxy on steel as it flash rusts).

Hopefully this is of some help to you.

[GPV]

Thanks Trent, very interesting. Will PM you.

Greg

[GPV]

Interesting,

I just got this back from a manufacturer of zinc phosphate epoxy primers:

"....The zinc phosphate in our AYB Epoxy Primer does not have any benefits for aluminium, only steel...."

So there you have it. Most rattle can primers in Australia are zinc phosphate based, including Wattyl Super Etch.

Given there is no cathodic protection and the coating seems a bit porous, I really do wonder how rattle can etch jobs will hold up long-term.

A non-chromate 2 pack epoxy might be a reasonable compromise as it at least provides robust isolation from the elements. Otherwise, it looks like it's chromate or no primer at all.

[PaulvS]

I started out in mid-90's using a Wattyl eurocryl self-buffering etch primer that was zinc chromate based, but it is no longer available due to health risks (carcinogenic). Recently investigated everything I could locate in Australia; Akzonobel, PPG etc. and anything aerospace related is around $700 per gallon. The Stewart Systems water based primer is around $300-$400 per gallon, I understand it is a bit harder to apply, but works well.
For painting the exterior, I've settled on Nason 2-pack epoxy primer. This will be top-coated and it provides a very tough barrier, but it's a hassle to put on because it is toxic (isocyanates - needs a forced air breathing system) and pot life is limited. That makes it impractical for preparing small parts.

My understanding of single pack etch primers, e.g. Wattyl self-etch, is that they are designed to be over-coated. They are porous, so they don't provide any real protection from corrosion on their own.

I've had good test results with Dulux all surface metal primer. If the aluminium is scuffed with red scotch brite and degreased, it sticks very well. After a week of curing it is very abrasion resistant. Cost is less than $100 for 4 litres. I have decided to use this to prime the inside of the fuselage where there are lapped joints in Alclad 2024, and for all 6061 and anything that is steel.

Alodine would also be an option, but it too is toxic and very time consuming.

I am aiming for an airframe that will last about 20 years. I would rather fly a bit sooner, than over-kill with corrosion proofing.

[RV3Bob]

I have found non 2 part primers, ie rattle can primers almost hold up to water. It may be OK for totally sealed parts such as inside flaps etc. if you are priming an area such as cockpit interiors where you will scuff or get mild solvents on you will need epoxy. If you will be doing a bunch of painting get a Hobby Air with a full face mask. Respirators do not protect you from epoxy fumes. Think eyes.

Of course one of my best friends who paints with chromate once or twice a week says he just holds his breath. Sad to see his hands starting to shake.

Bob Grigsby
Cub flying
3B getting close I hope
Dues paid
Too many hoops for pic posting. Luddite syndrome