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Old Jul 19, 2012, 08:08 PM
Dreamin' in 3D
Blackhawk3D's Avatar
Lodi/San Luis Obispo
Joined Oct 2003
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Foam plug surfacing/sealing?

Hi guys,

I'm working on some foam plugs for some parts that have been machined undersized then built back up with an epoxy/cab-o-sil/microballoons mixture and then remachined to the final part dimensions. This gives a nice hard mold surface that is similar to molds made with ren style tooling board. This machined surface is nice and durable but is not glossy at all and is quite porous. I've been filling any imperfections with a variety of fillers (tried a few, gray automotive glazing compound works well, for bigger repairs, filled 5 minute epoxy) and then coating with duplicolor filler primer and wetsanding to a nice smooth flat surface.

Once I've achieved a nice, flat, consistent surface I've been coating the mold with some sort of gloss to attempt to get a good surface finish on my part.

The first part I did I used PVA directly on the mold surface, then waxed the PVA and pulled a good part. The second mold turned out much nicer with a good polyurethane gloss finish. I waxed it up with a release wax from Freeman Manufacturing and laid up my part, bagged it, and went to pull it the next day.

The wax release failed completely and the polyurethane top coat along with portions of the filler primer pulled off the mold with the part in quite a violent fashion (I was using air pressure to demold, it sounded like a gunshot when it separated).

First off, without a gun or other spray equipment, what is my best bet for getting a good gloss on the plug surface so that the part comes out with a good finish? Is one type of rattlecan/wipe on/brush on finish going to work markedly better with an epoxy part?

Second, what release system would be my best bet for keeping a nice finish on the part right out of the mold? PVA has resulted in dull surfaces so far. Should I be painting in mold to prevent direct laminating epoxy to mold surface interaction? When using PVA, should the wax go on before or after the PVA?

HELLLLLP! I'm tired of getting subpar parts and ruining hours of work on plugs when I pull parts.

Thanks!
Nathan
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Old Jul 20, 2012, 12:34 AM
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Cody, WY
Joined Nov 2007
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Since you don't have access to spray equipment about the only alternative is paint them with rattle can paint/primer, polish, wax, and apply PVA. Wax alone will provide a good release when working on top of single component paints.... as you found out.

You could make your mold with a polyester gel-coat/surface coat and then sand and polish the mold surface. You could then use a semi-permanent release system (Frekote) or use wax and PVA. Once the mold became seasoned (4 or 5 uses) you might be able to eliminate the use of PVA and just use wax in the mold.

When using wax and PVA you want apply 4-5 coats of wax then apply the PVA over the wax. Each cycle after than you need to only apply 1 coat of wax then PVA. Freemon recommends waxing on top of the PVA which is stupid advice.
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Last edited by wyowindworks; Jul 20, 2012 at 11:56 AM.
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Old Jul 20, 2012, 11:01 AM
Dreamin' in 3D
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Lodi/San Luis Obispo
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Could anyone explain the reasoning behind putting wax under the PVA? It seems that PVA will release off of the surface regardless and that you'd want the wax on the part side to give you the least amount of possible adhesion between the part and the PVA/mold.

Thanks,
Nathan
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Old Jul 20, 2012, 11:51 AM
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For one you can use the wax to increase the gloss on the plug. The glossy the plug the glossier the PVA will be. Apply PVA over a surface that is sanded to 600 will not be as glossy as one that was polishing to 8,000 grit. Trying to wax and buff on top of the PVA puts the PVA at risk of being torn. The PVA is creating a barrier that blocks chemical reactivity (the reason you stuck the first time). Once the PVA is torn the wax on top of the PVA would be jeopardized as well. If the wax is under the PVA, and the PVA is torn, you still have some marginal protection from the wax.

In reality you don't have to use wax at all. Often the PVA will release from both sides without wax. If the PVA sticks, or the release is difficult, you can just wash it off with water or add water to aid in the release.

It's very important the you get a complete barrier/coverage with the PVA.

Adam
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Old Jul 28, 2012, 02:55 PM
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Does Freeman actually say to wax over PVA?

Thats redic, lol
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Old Jul 28, 2012, 03:25 PM
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http://www.freemansupply.com/video/preparing/part.htm
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Old Jul 28, 2012, 04:14 PM
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Yeah be sure to wax that PVA so your gellcoat fisheyes like nutz.
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Old Aug 07, 2012, 01:33 PM
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How do you apply PVA over wax? When I wax first, I have to spray PVA (Partall #10) as many, many almost dry coats or the PVA fisheyes over the wax. Normally I wax, PVA, then wax, but sure would like to be able to apply the PVA in one coat.

My layups (cowls, pants, a rare fuselage, etc) I always sand, prime & finish after pulling, so wax-over-PVA fisheyes aren't an issue.

My wax is just a Sears or Meguiars car carnuba, not special mold wax. Is that my problem?

-Dave
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Old Aug 07, 2012, 02:24 PM
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Cody, WY
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Quote:
How do you apply PVA over wax? When I wax first, I have to spray PVA (Partall #10) as many, many almost dry coats or the PVA fisheyes over the wax. Normally I wax, PVA, then wax, but sure would like to be able to apply the PVA in one coat.
You can shoot your PVA is one shot if you use Part-all Paste #2 molding wax first. No need to wax the PVA.
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Old Aug 07, 2012, 06:50 PM
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Thanks for the recommendation, wyowindworks - I'll have to get some #2.

I've always thought the Sears carnuba I bought 40+ yrs ago on the shelf next to their resin & cloth must be good and my technique was the fault. Heck, it was labeled for use as a mold release as well as shining up your boat!

-Dave
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Old Aug 15, 2012, 03:23 PM
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United States, OR, Tualatin
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On my seasoned Rotor mold, I have been doing one coat of Part-All #2 buffed and dried for 30 minutes, then spray on PVA our of the bottle, use a pre-wetted rag and wipe the surface down. Thin coat of PVA and it dries in 20 to 30 minutes ready for primer paint or finish paint.
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Old Aug 19, 2012, 10:54 PM
Thailand
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On all my moulds I just wax and then spray very quick drying 2 pack paint straight onto the wax. The paint is instead of the gel coat. So no gel coat.
Never get any release problems.
There is a bit of a technique to the spraying but no fish eyes or runs.
Obviously if you put too much paint on it will fish eye.
I can put the paint onto the wax so easily now but it needs practice.
I found that brushing things into the mould is one of the main reasons things stick.
Spraying solves a lot of things but you have to do it right.
Jim Fox
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Old Sep 07, 2012, 06:29 PM
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For my plugs I use a 2K urethane primer over epoxy glass skin. several coats with decreasing wet sanding will produce a super shiny surface. I usually finish with a 1500 to 2000 grit finish. I let it cure for a couple of days then several coats of pure canuba wax buffed between each coat after a 30 minute sit time. Then a very lite coat of spray on release agent. leave that for 30 minutes then a gentle buffing. I then apply my tool coat which is epoxy resin with equal parts of baking soda. Two coats of that then a 3/4 oz cloth with clear resin and begin building up the thickness with 60 oz then finished with heavy glass mat that I pull apart to to shread the edges. Thickness of the mold based on part size.

I use a similar method to layup the part from the mold. wax the mold with canuba at least 4 coats or more. The the release agent and buff. I then use the clear resin and 2 oz cloth to pickup panel line and rivet details. Then when slightly sticky but not dry to the touch I then apply heavier cloth depending on what the part is to be. When almost dry trim the edges and clamp the mold together and add tape and resin for the seams. Now I'm playing with filling the skins with two part expanding foams.
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Old Sep 18, 2012, 09:22 AM
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This is the Foamit5 pored in the back of a canopy and allowed to expand free form with no restrictor cover. Dried to plaster type hardness then was cut and sanded to finished shape within 15 minutes of poring. Humidity 25% altitude 4200 ft ASL Temp 90 deg F. As you can see it is very uniform. I mixed it for exactly 45 seconds and had maybe a minute or more to work with it.
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Old Sep 20, 2012, 12:59 PM
Composites guy
North OC, Ca.
Joined Jun 2005
1,179 Posts
Sealer on the plug acts as a platform for the release to work from.

I keep re-learning its advantages.
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