imp pwr online

Using Epoxy 4:1 everything works out great with hardening, pulling parts etc., but stiring the resin and hardner together makes air bubbles in the mixture. These air bubbles stay as I brush it onto the mold. Lots of them. Not applying close to gel time. Way before. Then after the part is pulled you can see the air bubbles on the surface. Any sanding on the surface sands off the thin air bubble covering and then I have pinholes. I could use a light body filler to fill since they are car parts that get primed then painted...But there has to be a way to not get bubbles in the resin.

Here are some pics of the finished parts

Underside showing mounting bolts


More Pics













Any help would be great
thanks,

goony

OK firstly these parts all seem to be cosmetic as in they are not load carrying so firstly dont use EPOXY use polyester it is cheaper and quicker so the art of making it look good is to not have fibres all over the place the way to do this is thus
1st using only polyester mix clear gel with clear resin and use a clear cat when this has been applied and cured u will find that when u put the carbon on it wont stick this allows u to move it into position without damaging the fibre and making a mess use 100gm carbon wet it out so that it is soaked using a brush to stipple it through then add another layer and stipple the resin from the first layer through it allow to cure and there u go
hope this helps

regards goony

imp pwr online

I don't mind the extra money are time it takes to use the epoxy. The smell of polyester is just not worth the savings to me. I just need to figure out how to keep the small air bubbles out of the resin.

Oh, and it is just plain fiberglass not carbon.

goony

R U using a coloured GEL coat

regards goony

imp pwr online

Epoxy 4:1 with a black dye added

goony

The names are different to wot we use but the process should be the same
So how do u go about making these parts?

imp pwr online

My only problem in making them is the air bubbles in the resin due to the mixing process. It's in the resin and stays as it gells and sets. Then the surface has small air bubbles in it.

goony

OK I cant wait any longer as I need my bed as it is 2.40am over here so if this isnt how u do it then give it a try
1st coat the mould with your epoxy resin make sure it is all coverd evenly you can do this with a brush or spray it its up to u then allow this to cure then lay up as normal let me know how u get on

regards goony

imp pwr online

Yes, this is what I do, I put on one layer of resin let get tacky then second coat resin and let get tacky then thrid coat with cloth.

My problem is with the resin. It has tiny air bubbles in it from mixing in the hardner. These bubbles stay in the resin and when brushed on. After setting bubbles are still in resin. This shows thru on the top layer and if part is sanded the thin layer over air bubble is popped and now it is a pinhole.

Goggles

My Feedback: (4)

Just a quick thought, what is weight is your first layer of cloth?
If it's 6oz. or higher, that could be your problem. The pinholes are actually the holes between the weave. If this is the problem, us a 1oz or 2oz for the first layer. Just speculation though.

ptxman

My Feedback: (2)

There are a few issues here & it has nothing to do with polyester vrs epoxy.

How are you mixing the resin/hardener? 'Hand mixing' in a cup with a stick has a lot of disadvantages: it introduces unwanted extra air, isnt really all that effective a mixing mechanism & takes longer which can be an issue with fast cure resins or thick gels. Its better to use one of those propeller type paint mixers on an electric drill at low speed. Even for small volumes. They draw the liquid down roll it over & minimize the introduction of air.

Do you happen to know the viscosity of your resin mix? In order for an air bubble to exist & stay suspended in the resin, the resin has to be of sufficiently high viscosity rating. So use a resin system with the right specs & that is a relatively thin viscosity. Something like 300-500 cp is considered thin & gives good wetting & layup qualities with hand layup (non vacuum methods). Something like 1000-2000 is considered thick. You can reduce viscosity by heating the resin (reduces pot life=faster cure) adding a thinner (notrecommended, it weakens & causes curing changes) or putting the mixed resin in a simple vacuum pot & extracting the air that way (fun to watch). Then you have to use good practice not to re-introduce air in the layup operation. Generally with the right resin you wont need any of these air removal methods with a mixer.

The cure: basically you need some sort of coating against the mold before the layup itself. That way, a nice defect free surface is layed down & any micro bubbles in the epoxy wont show through as defects. Think of spraying a car finish. The coating can be in the form of a paint (clear or pigmented, urethane, epoxy, whatever..) or the resin. If you use paint, it will be thin & light but special attention needs to be made to the releasing agent to prevent beading. The boatbuilding & auto crowd tends towards thickened gels (gelcoat) which has a higher viscosity & faster cure. In model airplanes, particularly competition models, gels are considered way too heavy to be practical. Hope this helps.

747drvr

My Feedback: (5)

Try putting your mixed resin in a vacuum chamber and pull vacuum. The bubbles willl fizz out like when you open a bottle of pop. Try not to agitate the mixture much afterwards.

imp pwr online

That is exactly the info I was looking for ptxman. It's not any cloth or layup layers that have air "pockets" it is the first coat of resin that has air "Bubbles" from the mixing process.

You hit the nail on the head, I mix in a plastic mix cup with a popsicle stick. It gets LOTS of air bubbles in it and that's all she wrote. They never come out. I am using Fiberlay 4:1 ProrGlass. No viscositiy rating on the bottles.

The propeller mixer sounds like what I need. THANK YOU!!!!

MikeyD

I have had some success by slightly heating the mold before applying the epoxy. I'm not sure how big your mold is, as mine our relatively small (wings, Fuses). The other thing I have seen that would work is the adds on TV for vacum bagging your food. Most of those gizmos come with an attachment to seal items in a jar. The bubble thing is annoying, try making a rubber mold sometime that can be a real pain too. Ok, hopefully the other comments will help. Let us know how things work out.

Mikey D

ptxman

My Feedback: (2)

Heres a picture of the prop mixer I use. Should be available in any paint/hardware store. Note the pitch, it does have a rotation direction, the right way & the in-your-face way. Its not rocket science, chuck it in the electric drill on low speed, keep it near the bottom of the mixing cup & spin away. It nicely draws down & rolls the fluid with minimal air introduction. About 30 secs is worth a few minutes manual flapping with a popsicle stick. Then just put it in a cup containing strong solvent like acetone & the plastic material cleans up well.

imp pwr online

Just went to Home depot and picked one up. Next lay up I will let you know how it works!

Thanks to everyone!

stumax

I've had a lot of success spraying a coat of primer onto the mould surface before layup. Let it dry completely. When laying up, put your lightest cloth (never go heavier than 3oz on the surface unless you absolutely have to, then think about using 3/4oz on the surface) into the mould then stipple the resin thru it. The stippling action helps break bubbles, and the cloth acts like a "bubble filter" as well. Since doing things this way, Ive never seen pinholes, even when I scrape the layup to remove as much resin as I can. Be careful using a vacuum chamber (if you have one). Most epoxies should not be subject to more than about half an atmosphere of vacuum as it boils off the more volatile fractions which can reduce the properties of the epoxy. Hope this helps, Stu.

goony

If the moulds are made correctly there should be no rubbing down needed that way u wont get bubbles showing through?
so u have to ask your self if youre moulds are up to standard?
surely it would be easier to make the mould smooth and polished as u only have to do the one mould rather than having to rub down and polish each moulding that u pull from it or have to rub the part flat enough to spray it?

regards goony

imp pwr online

the molds are 100% perfect. But the air bubles in the epoxy resin bubble thru to the surface. The help with mixing should do the trick

p51flier

The tip of 747drvr can also be read in the manual of a great european epoxy/polyesther/glass dealer. That vacuum trick is also a must for making silicone molds.

lestingoy

My Feedback: (1)

There are several ways to avoid this.

Paint the epoxy into the mold. Then use a heat gun (hair dryer would work) and blow warm air over the epoxy. This will heat the resin and thin it momentarily. Most of your problem will go away.

Let the resin cure most of the way before proceeding.

I'm concerned that epoxy isn't the best resin for this part. You are in MD, so it is cool outside now. Epoxy is not much good at anything near high temps. Even the heat of the sun on the black part will cause heat way in excess of what epoxy can handle. It will melt and deform terribly.

Polyester resin isn't as sensitive to the heat.

Good luck

Lee

CurtD

My Feedback: (1)

To remove the bubbles from hand mixed epoxy just add a little isopropyl alcohol (the "anhydrous" kind - no water) or denatured alcohol to the mix and stir GENTLY until it's mixed in. This will reduce the resin's viscosity and the air bubbles will disappear. Once applied, the alcohol will evaporate rapidly from the resin and viscosity will return to normal. I've been doing this for some time now pulling mostly cowlings and it has virtually eliminated the pinhole problem in the first coat.

imp pwr online

There's an idea...I will try that also. Thanks

rfoot

I use DER 331 epoxy resin all the time at work and we postcure the tools made with this resin at 300 degrees. Epoxy can take the heat.

GiantScale

So what pinhole filler do you use on Epoxy. I hear poly (auto)products should not be used.

Thanks

Mike