Part Rejecting Epoxy

General Composites Discussions Composites Talk
#1

I made some parts last week using epoxy and carbon fiber/fiberglass.

I’m trying now to brush on a “gel coat” of just epoxy, nothing else added. The epoxy won’t stay put on some flat surfaces it wants to reject the epoxy coating. Any ideas?

I roughed up the surface with 320 grit sandpaper yesterday, then washed the part, let it dry more than enough time for all the water to evaporate. I rinsed the part pretty good after washing.

Could it be my paint brush? It’s new, didn’t remove the plastic wrapping until i actually needed to use the brush. It’s one of those cheap throw away bristle brushes… the ones with the plain wooden handle and whitish tan bristles.

#2

did you wash all of your pva off before sanding?

#3

didn’t use any on this part/mold. I did wipe the part clean with acetone and a clean rag about 30 minutes before applying the epoxy.

#4

what brand resin?

#5

I’m not sure Hojo… i buy it from jgreer.com The owner buys it from Shell or one of the big epoxy mfg’s.

Not sure it matters but it’s a “non-blushing” epoxy.

#6

hmm… 2:1 ratio from shell, probally epon 826/3140 maybe. the hardner is a very thick amber, and the resin is clear? The only thing I can think of is that it is because you sanded it with 320, I would probally sand it with 80-180. just peelply alone is enough to get a good bond without sanding. by the way, I got 20 gallons of 3140 if any one is interested

#7

Hey mate, is this important? :o

#8

Thank you. The side i applied the epoxy coating to is the mold side of the part.

20 gallons… is that the hardener or resin?

the hardener i am using is a very light amber color. “slow” 45 - 60 minute pot life. The resin is very clear.

If sanding with say 120 grit paper will sanding lines/scratches be seen thru the epoxy surface coat?

#9

hardener…Yes, you should wash the pva off before sanding with water since it is waterbased

#10

I doubt its the same resin system, this system is more applical for high temp, and takes along time to fully cure at roomtemp. no, you will not see the scratches, just wash it with acetone first, it would be best to use 180 though

#11

What happens if you don’t? Gets sanded into the gelcoat and contaminates it?

#12

hmmm, where would i buy just the epon resin from? Would you sell/ship just one gallon? how much$

#13

it just makes sanding easier for one. but whatever you do make sure you wash the surface well before painting/bonding

#14

http://www.miller-stephenson.com. 3140 works many of the epon lines. without a post cure you can expect a couple days for decent cure, and I think it is 7 day full cure with the 826. it is a very tuff resin system. you can also add a very small percent of water to speed cure. I would be willing to sell a gallon of 3140 for $65 plus whatever shipping may cost

#15

You’re a mind of information :yes:

Got another for ya :smiley:

I’m spraying my plugs with the best quality spray can high build primer I can find. I bake these off in my over for a couple of days at 50 degrees C. Then I sand and buff them to a good shine with 2000 grit sand paper. After that, wax, pva, then two good layers of brushable gelcoat. Then some CSM with VER.

The mold releases from the plug easy enough but I get some of the primer transfering to the gelcoat. Not a lot, just little chunks or strips here and there… generally on the more difficult corners and edges.

I think it might be because I’m wetting my CSM out with too much resin, and/or because I’m spending too much time rollering the mat against the plug. But I’m not sure.

The primer that transfers doesn’t stick or eat into the gelcoat, it either chips or sands out of the mold easily enough, it’s just a bastard because it leaves the plug in a state that needs repairs, rather than leaving it untouched.

Any clues?

#16

just so you know, I meant after a part is pulled, you should wash the part of its pva then sand.

are you using a wax, or semi? many primers are very porus. when I spray a plug, I only use duratec ez sanding primer, then a duratec high gloss black. I usely wet sand up 2000-4000 then buff. wash with soap and water all the rubbing compound off the plug(very important), then use a solvent cleaner twice. then I use a semi and seal it four times, then add the semi release 4 times. wait for it to fully cure, do not touch the surface with your fingers, keep moisture off the surface. build your mold. this is the best method I have learned, I never stick a mold

#17

try using laquer aerosol paint instead of aerosol primer. Make sure it’s laquer and not laquer enamel. Should be easy to find some. You still have to allow enough time for the paint to gas off and fully dry. I always wait like 2- 3 weeks, but laquer paint should dry much more quickly… like one week possibly. or do it the way Hojo said. Those semi perm releases are very expensive though.

#18

semi’s pay for themselves real quick and go a long way. duratec is made for plugs and works great, and you dont need to wait weeks. all you need to do is sand it with 320 to open it up, let it sit for a day, then polish it, after you season it you can pull a mold

#19

Awesome. I’ll digest that stuff, and make some inquiries into semi perm release agents :slight_smile: Cost doesn’t bother me too much, I’ve dropped a heap on this project anyway, another few hundred bucks will be money well spent if it saves me a few hours a mold :slight_smile:

#20

You are always likely to have problems if you are surfacing plugs with aerosol can spray paints.

Best way to do it if you dont have a compressor and spray gun with around 1.8-2.0mm set up, is to either hire the gear needed to do the job properly yourself, or pay someone to do it for you.

Different types of mould release are not going to help that much if the surface of your plug has been painted with aerosols. So save your money, and use it to get your plug surfaces properly prepared, which should mean an end to the problems you have been having up to now.

Finally if whatever forms the surface of your plug has any sort of wax additive in it, then you must pay very close attention to sanding it, as paint doesnt like to stick to anything with even a trace of wax present.