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Jan 29, 2019, 06:32 PM
Registered User
Thread OP
Question

Mixing epoxy without air bubbles


Perhaps a strange question, but:

When I mix epoxy resin and hardener I involuntarily induce air bubbles in the resin. Ok, these air bubbles slowly ascend and pop, but I there is a limited window before the resin starts to gel and I don't want to spend valuable working time just waiting for the bubbles to disappear. I suspect that these bubbles can cause pinholes in the laminate.

Do you try to avoid air bubbles when mixing resin and hardener. Is there a good technique for this?

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Jan 29, 2019, 07:48 PM
Duane, LSF IV
Wazmo's Avatar
Mix slowly enough to avoid shear cavitation. Easier is to degas after mixing resin using a vacuum pot. If you're laying up composites by hand, the bubbles usually get worked out when wetting the fabric.

How to Remove Bubbles from Casting Resin - Vacuum Degassing | Mold Making Essential (1 min 41 sec)
Jan 29, 2019, 08:19 PM
Slow builder
_AL_'s Avatar
Do a search of custom fishing rod building. Application of bubble free epoxy is high priority in that world.

I've found using plastic & slowly stirring helps. Stay away from wood sticks.

I recall a lot of builders making a mixer out of a microwave oven motor & ball bearings to mix with good results.

Al
Jan 29, 2019, 11:11 PM
Scott
Pylonracr's Avatar
Your answer depends on what the resin is being used for. If it is a wet layup with carbon and will be vacuum bagged I don't bother as the air in the resin will be pulled out. I typically lay up my carbon a tad on the wet side and let the vacuum pull the excess resin out. If it is not going in a vacuum bag I will degass the resin in a vacuum chamber prior to use.

Scott
Jan 29, 2019, 11:43 PM
Registered User
If you stir by placing the stir stick all the way to the bottom and move the stick around while keeping the stick all the way in you get less gas. If you move the stick up and down while stirring you whip lots of air in.
Jan 30, 2019, 12:23 AM
Registered User
Try warming it up before mixing so it will be less viscous. Or use a lower viscosity epoxy to begin with. I've been using EcoPoxy lately, and love its low viscosity (and lack of fumes). Perfect for wet layup. Although it is yellowish colored, if that matters.
Jan 30, 2019, 08:18 AM
Registered User
Thread OP
Thank you all for your advice!


I'll try to stir more slowly using much broader sticks and flat bottom mixing containers. Part of my problem is probably that I have used thin sticks and tilted the jar and stirred fast to mix properly. I am not sure where I could get plastic stick to mix with, so I think I'll keep using wood.

I like the idea with the vacuum chamber to degas faster. I have a vacuum pump but I am very short of space in my workshop and I don't want to clutter it further with yet another bulky item. Maybe it is possible to mix the resin in a glass jar and screw on a lid with a fitting that attaches to the vacuum pump.

I have actually tried to warm the resin before the mixing to reduce viscosity and it helps with less air bubbles, however I don't like this because it reduces the working time and I don't enjoy working under stress.
Last edited by bergfalke4; Jan 30, 2019 at 08:18 AM. Reason: Layout
Jan 30, 2019, 08:21 AM
Slow builder
_AL_'s Avatar
Quote:
Originally Posted by bergfalke4
Thank you all for your advice!

I am not sure where I could get plastic stick to mix with, so I think I'll keep using wood.
Wood will give you bubbles.

Grab a packet of plastic spoons or knives for a couple of dollars & you'll have plenty.

Al
Jan 30, 2019, 09:54 AM
Registered User
Roguedog's Avatar
Anytime you mix a batch you are going to inject air into the mixed batch. Even if you mix slowly or use a plastic stick.

Do not heat the resin to remove entrapped air. Heating 30 minute epoxy for 8 to 10 seconds in a microwave will turn it into 3 min epoxy if your lucky.

As already mentioned a vacuum pot is the best way to degas the mixed batch.

There are 2 other ways I know of for removing entrapped air in epoxy. Both are done after the resin has been applied.

The first is to very lightly mist the layup with Acetone from a spray bottle.

The second is to use a heat gun and from 12 inches away and wave it over the layup. The idea here is to just lightly wave the hot air over the area a few times, not to get the resin hot.

You can actually see the bubbles popping as you brush the heat gun over the surface.

The two methods reduce the surface tension of the wetted out resin just enough to release a good portion of the entrapped air.
Jan 30, 2019, 11:19 AM
Registered User
Thread OP
Haha, can't believe I didn't think about plastic cutlery. Great idea! I think we already have a few packs home.

Do you know why it is a bad idea to use wood and why plastic is better?

Quote:
Originally Posted by _AL_
Wood will give you bubbles.

Grab a packet of plastic spoons or knives for a couple of dollars & you'll have plenty.

Al
Jan 30, 2019, 11:25 AM
Registered User
Thread OP
Thanks for the heat gun idea. I'll test that.

Not particularly happy about spraying a light mist of acetone over the layup. I try to minimize my exposure to solvents.


Quote:
Originally Posted by Roguedog
Anytime you mix a batch you are going to inject air into the mixed batch. Even if you mix slowly or use a plastic stick.

Do not heat the resin to remove entrapped air. Heating 30 minute epoxy for 8 to 10 seconds in a microwave will turn it into 3 min epoxy if your lucky.

As already mentioned a vacuum pot is the best way to degas the mixed batch.

There are 2 other ways I know of for removing entrapped air in epoxy. Both are done after the resin has been applied.

The first is to very lightly mist the layup with Acetone from a spray bottle.

The second is to use a heat gun and from 12 inches away and wave it over the layup. The idea here is to just lightly wave the hot air over the area a few times, not to get the resin hot.

You can actually see the bubbles popping as you brush the heat gun over the surface.

The two methods reduce the surface tension of the wetted out resin just enough to release a good portion of the entrapped air.
Jan 30, 2019, 11:39 PM
Scott
Pylonracr's Avatar
It doesn't take much vacuum to degass resin. A few inches is enough. I have a couple different sized mason jars with fittings added to the lids. I mix the resin in my mixing cup, set the cup in the jar, screw on the lid, and pull a vacuum. Go slowly, as the resin tends to foam up if there is a lot of air in it. I hit it with about 2 inches and let it settle, then go to about 5 inches. The entire process takes about 1 to 2 minutes.

I'm with you on the acetone. I would never consider contaminating a layup with it.

Scott
Jan 31, 2019, 08:29 AM
Registered User
Roguedog's Avatar
I don't use Acetone either just mentioning it because I've seen it work.

The idea that it would contaminate is a ridiculous one as Acetone is the fastest evaporating solvent manufactured.

There are many web pages declaring that you can use Acetone, Lacquer thinner, Paint thinner, or even rubbing alcohol. But every epoxy manufacturers TDS that I have read never say use a thinner if it's too thick.

The heat gun works just as I mentioned above and is what I use all the time. Fast and easy.

I have not found the need to use a Vacuum pot yet as the heat gun works very well.
Feb 02, 2019, 07:09 AM
Registered User
Thread OP
I followed your advice and built a vacuum chamber to degas the resin. It was not very difficult once I had made up my mind...

It is a plastic container for food with a silicone sealing. Paid 4 for it so it was a moderate investment. I drilled a hole in the lid and attached a vacuum bag fitting that I had laying around. It is not super-sturdy and I would have preferred a glass jar, but all glass jars had glass lids which I would not have been able to drill. However, I tested it to 10 inches of mercury without any problems so I think it will be fine.

I also purchased a set of plastic knifes to mix the resin. Still not sure why plastic is better than wood but it is worth a try.

Thanks!
Feb 02, 2019, 10:49 AM
Registered User
Roguedog's Avatar
Nice! Post some degassing pics.


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