Wing plug finish 2

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#1

Hi guys

I finally finished one side of the wing plug after several thousand hours of sanding. I wet sanded the plug up to 800 grit mounted on a flexible plexiglass plate. then I dry sanded with my mirka 1000 and 3000. Afterwards i applied two polishing compounds.
Before I painted the fiberglass plug with a 2k “affordable” car primer (white) and then black 2k polurethane paint.
The problem is the primer shows thru the paint on some places as little white spots (shown the worst sections). Is this a no go to pull off the mold? I will use nord rm2500 or 3000 poliester to pull off the moulds.

Regarding Nord RM2500 could i use 3d-core, lantor or some similar sandwich in order to stabilise the huge mould? I would like to heat the mould up to 80ºC and am afraid that the sandwich could produce distortion due to the asymetric layers around the sandwich.

thanks and regards

#2

“several thousand hours” ???

Is that a joke or you are serious

#3

If you are afraid of distortion, why are you going to use polyester?

#4

Its the only affordable option. This is homebuilding

#5

What release system are you going to use ?

#6

I believe its forum consensus that semipermanent frekote is the best. So i would use frekote

#7

whatever release system you choose, make sure you do a small test area prior to making the entire mould. I would be slightly concerned about your choice in topcoat, you never know how well it will work with your release system and process. I personally would of chose Duratec high gloss black, or just Duratec primer.

#8

+1 as hojo said :slight_smile:

Also.
I’ve had mixed results with release of 2k paint. Using epoxy tooling coat due to the fact they really bite into the 2k hard , if you are going to use poly you might no have the same problem.
If using frecote I’d put a few coats of wax over the top of it to ensure perfect release.
I do this every day building RC. Gliders.

Tim

#9

I have noticed that the 2k paint is really reactive to disolvents and acetone. I cannot wash the surface with acetone because the paint strips of. Is that a bad sign prior to demoulding?

#10

I’ve been having that problem with a rattle can primer that I use too (although I’m not sure that it qualifies as 2K). I know that a 2k clear that I’ve sprayed before held up perfectly well under acetone, but I’d like to know if automotive style 2k poly primer would dissolve under it as well, similar to how the rattle can primer is reacting. I was actually surprised that even the rattle can primer dissolved in such a fashion under acetone, it really just wiped clean off.

#11

Yes.
I use 2k every day , and grew up in and around a smash repair shop.
It sound like to me you have not used 2k paint. ???
2k doesn’t get effected by acetone or does it with GP thinners. If I where to rub down one of my wings with thinners I don’t get any colour on the cloth…
All acrylic car paints etc WILL be damaged by both thinners and acetone type solvents.

Can you post pics of what paint you used ?? It might help with a resolution.

If if it is acrylic , you could do a small test piece and put some of your polyester you are going to use and see the reaction.
The problem comes when you do a mould and the wet polyester sitting on the acrylic for a long time , just desolves the paint.
If it is 2k it will be fine.

So if it is acrylic…
You would have to use a epoxy surface coat or tooling coat and that would be fine and causes no reaction with paint. As we have done it plenty of times with RC glider fuses and wings.

Tim

#12

They sell it as “poliuretano alifatico de 2 componentes”. It s very hard and used to paint stairs for example and its a pain to sand. Seeking for a translation i got aliphatic and chemical definitions i am not fond of???

#13

In English, this translates to “two-part aliphatic polyurethane” which, to be more complete is “two-part linear aliphatic polyester polyurethane.” This is the “high-priced spread,” used for very hard, very abrasion resistant, very tough, very durable and very glossy (usually) coatings of all kinds. Clear, it’s used for stairs and floors, bowling alleys, gym floors, etc. Pigmented, it’s used to coat airplanes, boats (above the waterline), sometimes cars. Awlgrip is a widely used paint formulation I have experience with. There are others. I don’t have experience using these as mold coatings and I don’t know how the molding versions differ from the top end paint formulations (if at all). I’d like to learn more about that usage of the polyurethanes.

In paint usages, there are also “two part acrylic polyurethanes.” These are a bit softer, a bit less abrasion resistant, tougher coatings. They are somewhat easier to apply, can be rolled and tipped to give an “almost sprayed” finish and for a less demanding surface, they can be brushed. A paint example of these is AwlCoat 2000, somewhat less expensive than Awlgrip. Again, there are other brands.

If you use it properly, once cured either form of two-part polyurethane won’t dissolve or soften in acetone, any common thinner, petroleum products, most acids, most bases or spit. If you get it wiping up with acetone, you should review your mixing and application procedures and make sure you’re following directions carefully. It sounds like you’re adding something “extra” that is short-stopping the curing reaction after it’s applied. Do you have the right converter? The right thinner?

While I know a bit of polyurethane chemistry and uses of polyurethane paints, I’d like to learn more about their use in composites molding. Anybody? Anybody? Buehler?