Cory Bird's Raw Epoxy Finishing Technique

[rickh]

5-Star "Maxx Fill 2K" High Build Primer Surfacer is but one, I know Dupont and PPG have similar. *I'd* shy away from single stage primer-fillers, but that's just me.

 

Disclaimer: I haven't painted ma plane yet, but the two part (2k) primer fillers are 'da bomb at filling pin holes on smaller epoxy-fiberglass parts I make. First coat is reduced, to fill the holes rather than bridging them, the last two coats are more/less 'full' strength. Then sand with 400-600 grit to level, squirt the top coats, done deal.

 

Rick

[Kent Ashton]

If you try to sand the micro to 320 you will have a very hard time keeping the surface true.

Hmm, I've never found it that hard to do: When the surface is relatively flat, rub it with an 18" (or so) aluminum bar. It will leave smuges on the high points (the same high points left after completing your 60-G sanding). Gently sand the high points and rub with the bar again until the smudging is uniform. Now you'll have a flat 320G surface ready for pinhole-killing.

[Lynn Erickson]

Hmm, I've never found it that hard to do: When the surface is relatively flat, rub it with an 18" (or so) aluminum bar. It will leave smuges on the high points (the same high points left after completing your 60-G sanding). Gently sand the high points and rub with the bar again until the smudging is uniform. Now you'll have a flat 320G surface ready for pinhole-killing.

Its not hard to do on the relatively flat surfaces with a straight edge. I want to see that 18" straight used to do the compound curves, or better yet the inside curves. my point is that it is not necessary to go to 320G to get a true flat surface when using the high build primer, they recommend only go to 220G so there will be good tooth for it to adhere. sanding the surface down to 320, adding epoxy and then sanding it again before primmer is adding extra steps that are not needed. this all happens in one step with the high build primer

[Lifessamsara]

This might be a trivial point, but given the surface areas we are discussing here, what is the weight difference between both techniques? I recognise that Lynn's approach requires less effort (you get flying sooner) with no difference on quality of finish, but is the trade-off an increase in weigh, and if so, how much? How much heavier are these hi-build primers compared to dry'ish micro?

Merry Christmas all,

 

Bruce.

[Lynn Erickson]

This might be a trivial point, but given the surface areas we are discussing here, what is the weight difference between both techniques? I recognise that Lynn's approach requires less effort (you get flying sooner) with no difference on quality of finish, but is the trade-off an increase in weigh, and if so, how much? How much heavier are these hi-build primers compared to dry'ish micro?

Merry Christmas all,

 

Bruce.

they are not heavy and the idea is to use dry micro and get the surface as true as you can with a course sand paper. meaning the surface is true but has 60 grit scratches and pinholes. use the high build to fill the scratches and pin holes leaving a smooth uniform layer of the primer. most of the new two part epoxy primers come in a high build and regular formula.

[jpolenek]

Back to the Cory Bird method...

If you're using MGS335 fast epoxy and let a coat cure to the point where it has lost most of its tackiness (e.g. 1 hour), is there enough potential crosslinking left in the epoxy to provide good adhesion with the next layer? In other words, does it have to be wet-on-wet, or can it be wet-on-semi-tacky?

 

Joe Polenek

[Wayne Hicks]

Wet on semi tacky is fine. You're not lookiung for strength, you're looking for coverage.

[Richard Schubert]

use the high build to fill the scratches and pin holes

My understanding was that the epoxy method would fill the pinholes, whereas primer has a tendency to bridge over pinholes, leaving an air pocket that could be broken into during sanding. Maybe newer primers don't have this potential problem?

[Wayne Hicks]

The posts on my web site assume the builder is spraying the primer on. The question I've wanted to ask Lynn is whether his technique is to roll the primer on or spray the primer on? I can see where rolling on the primer will fill pin holes. Rolling allows one to work primer into pinholes when you see them.

 

I also witnessed a Lancair IV builder whose painter sprayed the primer on. But every time he saw a pin hole, he dabbed at it with a small brush like the type that an artist would use. Sometimes he'd use the corner of a squeegee. Either way, the surface (primer) was disrupted. They had to come back later and sand the disruptions away. You have to sand the primer anyway, so maybe it's a wash. This particular painter applied ALOT of primer. I didn't agree with his technique.

[Lynn Erickson]

The posts on my web site assume the builder is spraying the primer on. The question I've wanted to ask Lynn is whether his technique is to roll the primer on or spray the primer on? I can see where rolling on the primer will fill pin holes. Rolling allows one to work primer into pinholes when you see them.

 

I also witnessed a Lancair IV builder whose painter sprayed the primer on. But every time he saw a pin hole, he dabbed at it with a small brush like the type that an artist would use. Sometimes he'd use the corner of a squeegee. Either way, the surface (primer) was disrupted. They had to come back later and sand the disruptions away. You have to sand the primer anyway, so maybe it's a wash. This particular painter applied ALOT of primer. I didn't agree with his technique.

the first coat is rolled on and scrubbed into the surface to fill the pin holes. second coat is rolled on smooth and a little thicker to fill the sanding scratches and check for missed pin holes. the first two coats are sanded with 120 grit just to remove the tops of the high spots that the roller left. the third is sprayed on and then sanded to a smooth true surface finish ready for the paint primer. the first two coats do the same thing as the raw epoxy does, it fills the pin holes but also does add some filler on the surface and is much easier to sand then epoxy. rolling on the primer does not build up as much primer as you can when you spray the primer on.

[Big Steve]

Lynn:

 

You still have not told us what brand of High build primer you prefer??? Enquiring minds would like to know. STeve build on