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May 24, 2019, 03:42 PM
plane destroyer and builder
skybattle's Avatar
Thread OP
Sounds sensible, Roguedog. I will not heat the resin the next time.

All in all, I have to test all your interesting ideas.
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May 30, 2019, 04:38 PM
plane destroyer and builder
skybattle's Avatar
Thread OP
Here the test.

- 1 hour of resin gel before adding the core
- Balsa sealed, without perforating it
- I applied a metal roller after vaccum bag

In the first picture you can see:

- On the left, no clear coat and 25gr fiberglass
- On the center, clear coat + 25 gr fiberglass
- On the right, clear coat and no fiberglass

You wil see very few pinholes.

I think applying the resin with a sponge roller I can improve the wetting of the spread tow carbon fiber (or generating more bubbles?), applying it in the two axes of the fibers.

My conclusions are:

- 1 hour before pasting the core
- No need of 25gr fiberglass
- Clear coat is convenient
- The metal roller is necessary
- Wetting very well the fiber is necessary

I would greatly appreciate your opinion.
Jun 19, 2019, 02:51 AM
plane destroyer and builder
skybattle's Avatar
Thread OP
Well, a lot of problems with the adhesion of clear coat to 2k paint and to resin.

The clear coat peeled off the paint and with the resin does not adhere well, so I have to apply clear coat again to the paint.

There are some strokes of air too through the spread tow.
Jun 19, 2019, 07:13 AM
Registered User
Roguedog's Avatar
Like the way the wing looks.

So so can you specify whether the clear coat is, e.g. epoxy resin, 2k paint, some other substance?

The reason I ask is that unless its epoxy paint as the first coat in the molds your trying to get paint to adhere to a plastic (cured epoxy composite).

Most paint does not like to stick to plastics. They make adhesion promoters for that purpose.

If not painting in the mold you would normally sand the plastic (epoxy composite) to what ever grit u want, spray on the adhesion promoter, then spray the topcoat paint.

If the first layer is paint how long til fully cured. If any solvents are gassing off they can cause air bubbles. If the clear coat is pealing off the composite, does it stick in mold? or are you just pealing it off?

I understand why painting in the mold sounds like a good idea e.g. to have a UV protection layer for the epoxy.

Why are you are top coating over 2k paint?
Jun 19, 2019, 07:23 AM
plane destroyer and builder
skybattle's Avatar
Thread OP
Thanks for your answer, Roguedog.

It is 2k clear coat. Sounds like you say, a plastic not sticking well to the 2k paint and bad to the resin.

There were 1 day from 2k clear coat to 2k paint. No sticking in the mold (I use semi-permanent mold release).

I use a 2 layers paint, so, as I understand, the clear coat is necessary. And my infusion resin is not UV resistant, so I would need to use a UV resistant one.
Jun 19, 2019, 07:40 AM
Registered User
Roguedog's Avatar
I dont think that any epoxy is UV resistant, but I havent investigated that.

There's a lot of people that claim painting in the mold is the bees knees, and claim excellant results. How long to u let the semi permanent mold release gas off for?

Seems like some kind of compatibility issue between the resin and 2k paint.

Do you apply the release prior to the painting?

How long does it say to let if gas off before you start the first layer?

edit---
Last edited by Roguedog; Jun 19, 2019 at 10:53 PM.
Jun 19, 2019, 10:53 PM
Registered User
Roguedog's Avatar
Sorry i hadn't read the post in while. I scoured the TDS for the resin system you are using and dont think that's the issue. So it msut be the paint.

If it was me --

1. I'd spray the the color, as soom as it flashes off --

2. place a coat of resin only on top of it, let that gel, then continue the layup.

Don't wait for everything to dry before going to the next process. Spray the clear afterwards not the first.

Using auto paint you would normally put the clear on last. If there were multiple maskings before the clear coat a color sand would help knock down paint edges from masking tape and any orange peel.

maybe one of the experts on spray in the mold paint can chime in here. I'm out of ideas
Last edited by Roguedog; Jun 19, 2019 at 11:02 PM.
Jun 19, 2019, 11:13 PM
Registered User
Roguedog's Avatar
I'd say spray the clear first but dont know the flash time of the clear.

You usually don't mask over clear so all this in the mold painting is ass-backwards. If the clear has a hardener then you should be able to mask on with in a few hours,if it wasn't too thick.

I'd imagine those getting the best results are in a hurry to get it done. So the idea is start and finish in contiguous process, e.g. going from clear coat, to color as soon as you could apply the masking tape, to color, then as soon as you could lift off the mask, to too layup in one session.

It's the only way that makes since to me.

If the paint is fully cured then as well as the epoxy resin a sand is needed for the next layer to adhere.
Jun 20, 2019, 03:14 AM
plane destroyer and builder
skybattle's Avatar
Thread OP
I think it is not a degassing problem, because I applied the semi-permanent days ago before the painting.

Your idea is good, but I have to play with the 'tacky' times trying to avoid the print-through.

It is true that the 2k clear coat and the 2k paint I use dry very soon. This can be, certainly, the problem.

I will make tests again with your suggestion and will post the pictures.

Thank you very much!
Jun 27, 2019, 04:37 PM
Registered User
I used to get bubbles all the time. Drove me nuts... I tried degassing the epoxy in a vacuum, no deck cloth, heavy on the epoxy, different kinds of rollers. No matter what I did I always ended up with bubbles.

Finally figured out that it was the roller introducing air into the layup.

I now roll out the molds really wet with the roller or just spread it on with a foam brush if its a tail. Put it on heavy so that its to the point of pooling. Let sit for couple minutes and hit it really quick with a heat gun on high. 5 seconds max on heat per panel.

Lay the spreadtow on the mold and let it soak up the epoxy. Note I don't use deck cloth with the textreme. Just lay it on the clear coat painted molds.

No more paint roller after this as it just pushes small bubbles into the layup. If you need more epoxy pour it on and spread with bondo spreader.

Work the fabric into the mold using a bondo spreader. You can do this with Textreme with no worries, not sure about other fabric. Excess epoxy will build up on the spreader as it soaks up through the fabric and is wiped off with a paper towels. If dry in spots just add epoxy on top and spread as needed.

Haven't had bubbles since I went with this method.

Thane
Jun 27, 2019, 04:56 PM
Barney Fife, Vigilante
tom43004's Avatar
I use trim rollers with very tight cells... don't have issues. Most of my layups are curvy enough that I can't use spreaders.

Lots of ways to skin the... wing.
Jun 28, 2019, 03:43 AM
plane destroyer and builder
skybattle's Avatar
Thread OP
Thank you. I will avoid using the paint roller and I will test the bondo spreader.

The spreadtow I use I think is very good :

https://www.castrocompositesshop.com...2-cm-wide.html
Jul 03, 2019, 05:35 AM
Registered User
Skybattle, please keep the updates coming. Seems I'm on a similar path to enlightenment (albeit via baging plain weave carbon over XPS foam and those pesky tiny little bubbles that perforate the entire surface) so I'm stoked to have stumbled onto your thread when I have. Good luck!
Jul 03, 2019, 06:45 AM
Barney Fife, Vigilante
tom43004's Avatar
Ross, what PSI / Inches Hg are you bagging at? Do you use peel ply / breather cloth across the whole wing? Yours looks to me like it could be more related to lack of compression.
Jul 03, 2019, 07:50 AM
Registered User
Cheers Tom
I'm conscious of hijacking Skybattle's thread.
I've got the vac pulling about 10 inches I think (pump kicking in at about 8, off about 10). This layup was: bag material, paper towel, thin non perforated plastic, Mylar + Meguires #8 release, a single layer of 200 gsm plain weave, foam core. I hit this with a heat gun and light squeegee pressure once bagged to get excess resin to flow out into the paper towel and cooked it at about 50 deg c for a few hours. Mylars came off about 12 hours after bagging.


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