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Vacuum Bag and Hard But Not Cured Resin

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OzBungy
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Vacuum Bag and Hard But Not Cured Resin

Postby OzBungy » Sat Aug 22, 2020 8:08 am

I have been dabbling with vacuum bagging my foil repairs. So far I do a lamination then leave it overnight.

The West Epoxy instructions say that "green" epoxy, resin that has hardened but not fully cured, will chemically bond to a new layer of epoxy.

It would be nice to get more than one resin coat done in a day, and take advantage of the chemical bonding.

I don't like the idea of pulling the part out of the vacuum bag, tearing off the peel ply, and risking damaging the partially cured job.

I don't think I need the chemical bonding, but it might be nice to have. Anything that results in a stronger job is good. The peel ply leaves a good textured surface and I rub bumps off with 50-80 grit paper and that has been working fine so far.

Are any of you vacuum bagging experts pulling stuff out after partial cure for more work?

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Re: Vacuum Bag and Hard But Not Cured Resin

Postby tomtom » Sat Aug 22, 2020 8:38 am

peel ply also give you nice finish for next layer epoxy - its often used precisely for this.
And its not 0 and 1 - for sure you can find good balance. But you need temperature control if you need to know precise cure state.

But frankly for foil repair - multiple vacuum bagging sounds like WAAAAY overkill.

OzBungy
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Re: Vacuum Bag and Hard But Not Cured Resin

Postby OzBungy » Sat Aug 22, 2020 9:31 am

Thanks for the comment. The second bagging was to apply a mini-patch to cover a tiny gap where the carbon wouldn't bend around a tight corner.

After that I'm planning on hot and/or fairing coats depending on how everything turns out. If there was an advantage to doing the final coats on green resin then I would do that.

All this is a bit of a lockdown project to ramp up my foil repair skills. I've pulled out a bunch of old filler repairs and rebuilt and rewrapped the tip of my foil in carbon. It's all turning out well so far.

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Bille
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Re: Vacuum Bag and Hard But Not Cured Resin

Postby Bille » Tue Aug 25, 2020 11:54 am

edit :
Now that was a complete and total waist of time .

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Re: Vacuum Bag and Hard But Not Cured Resin

Postby dirk8037 » Thu Sep 03, 2020 9:02 pm

Hi,
I guess in a day might be a bit tight.
But ther are some resins that cure very fast and are, at least thats what they say, not stick anymore after 4-5 h.
Check Resin Research eg at Greenlight Surfsuply or Sicomin Superfast .
Prof. Surfboard builders like to have shor processes and dont want to wait a day until they can laminate the other side.
Trade off will be always in mechanical qualities, but I guess that is neglectable with repairs.
Higher Temps (>30) will also speed up the process.

Also I was told that the chemical process that enables bondage of layers takes much longer that the curing time.
So if you use those resins, peelply and maybe a layer plastik on top to sweeze out excess resin you should get a decent finish.
If you snand carfully you could get away with furhter coatings or sanding coats since teh rough surface of the peelply gives you a little bit to take off with out sanding the glass.
Grid 240 then up to 400 and 600 maybe.

Cheers Dirk

OzBungy
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Re: Vacuum Bag and Hard But Not Cured Resin

Postby OzBungy » Sun Sep 13, 2020 7:08 am

did the vacuum bag layers to full cure (or as full as it gets overnight), with a peel ply surface. The two carbon parts bonded together nicely with no significant voids, bubbles or pinholes.

3m Super 77 adhesive stopped the edges of the carbon fraying and helped the carbon stick to the surface while pre-forming the carbon to the tip.

I did a fairing coat to fair the transition from the new carbon to the existing surface. Let that cure hard and sanded it with 80 grit and a bit of 50 grit for bonding texture.

Finished off with a couple of resin coats, letting the first coat partially cure before adding the second. Wet sanded the cured epoxy. It was easy to sand the epoxy and the finish was nicer than the filler coat.

Wet sanded and a few coats of rattle can spray paint and the result looked as good as new. Very pleased.

The days were fairly cold so I heated the work and the resin using various means (heat gun ,hair dryer, heating ducts, resin bottle in hot water, hot water bottle, etc). That all worked fine. I use slow cure hardener simply to give me more time to do stuff. It's unnecessary but it's what I've got and I'm in no real hurry.

It is so nice to get out for a few sessions on a fully refreshed foil.


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