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Old Jan 02, 2009, 06:03 PM
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Epoxy resins vs. polyester resins


I have found epoxy resins, used for fiberglassing, to be quite expensive. I am wondering how polyester resin compares to epoxy resins? I can get polyester resins for much, much cheaper than epoxy.
Does a polyester resin weigh more than an epoxy resin? Which is stronger, in terms of mold making?
I do realize that polyester resin has it's setbacks too, such as it eats foam....

FJ
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Old Jan 02, 2009, 07:32 PM
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Polyester is more brittle, less strong.
Old Jan 02, 2009, 10:01 PM
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Polyester resin will also eat foam if you want to do a lost foam cowl or other shape. For that application epoxy laminating resin is the only way to go.

The strength in the part should come from the density of the fiber and not the type of resin used. Having said that polyester is more brittle as noted by Pinecone so you need to be more attentive to the layup around mounting points.

Both resins are very fuel proof. If you use the polyester be sure to use the unwaxed style resin or you'll have a tough time getting paint to stick to it later on.
Old Jan 02, 2009, 10:24 PM
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Also don't use polyester for thin parts like skins and bulkheads because it continues to shrink for several months and WILL warp
Old Jan 02, 2009, 10:25 PM
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Thanks guys! I'm going to use epoxy resins.

FJ
Old Jan 03, 2009, 02:32 AM
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What would you usually use the polyester resin for?. It sounds like there's not too much left after skins, bulkheads and sheeting foam. I'm not being a smart a#$, I'm new to this area of the hobby and I'm really curious as I have a can of the poly and was going to use it for foam/wood sheeted wings. Warping and melting seem a possibility.

Keith
Old Jan 03, 2009, 08:10 AM
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They build boats and car boddies with it.

I haven't used poly around models ever. Always epoxy.
Old Jan 03, 2009, 08:49 AM
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I moulded an undercarriage out of polyester.

Perfect for the job.

But other than that, epoxy.
Old Jan 04, 2009, 08:39 PM
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I use polyester resin to build molds or to make fuselages, work great. Aeropoxy ( BVM) or Hysol for joining fiberglass and plywood. Pacer Z-poxy 30 minutes finishing resin to cover balsa with fiberglass cloth...the best .
Old Jan 04, 2009, 09:03 PM
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Epoxy resins wick into wood grains better as well. I use thin epoxy when glassing wood boats. Poly isn't fun to breath in. Epoxy resin has a mild order and should not be harmful.

Neither resin bonds well to the other.

-Rocko
Old Jan 04, 2009, 10:02 PM
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Quote:
Originally Posted by bidule
I use polyester resin to build molds or to make fuselages, work great. Aeropoxy ( BVM) or Hysol for joining fiberglass and plywood. Pacer Z-poxy 30 minutes finishing resin to cover balsa with fiberglass cloth...the best .
How strong do your polyester fuselages come out? Have you compared it to an epoxy?

Thanks for all the help,

FJ
Old Jan 04, 2009, 10:42 PM
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They are strong if you use the appropriate fiberglass and if you use carbon tow and carbon cloth @ the right place. Many ARF are made with polyester resin .Epoxy is very expensive..
Old Jan 05, 2009, 12:52 AM
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Poly Resins are dinosaurs. Forget about them. The catalysts (MEK) are more hazardous, the resin smells horrible, and are not as stable in the sunlight. (I might have that last one backwards)

What they are for- is for fiberglass mat. Epoxy resins will not disolve the glues that hold the mat together, and will not allow it wet and relax to the complicated shapes that you use mat for. No one on these forums uses glass mat.

I don't doubt that ARF manufacturers would use polyester resins to cut cost. Remember that those folk are also (probably) in industrial areas with the facilities to deal with this trash. Then again, they may just be poisoning themselves...
Old Jan 05, 2009, 06:12 AM
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Epoxy resins can create alergies to epoxy, which can limit your later use of them. Just because there isn't an odor, doesn't mean they are perfectly safe.

Avoid skin contact and use in a well ventilated area for both types of resin.

ESPECIALLY with poly, wear safety goggles when handling the catalyst. A single tiny drop in your eye could cause lose of vision in that eye. MEKP is VERY reactive to body tissue.
Old Jan 05, 2009, 10:50 AM
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Quote:
Originally Posted by kwmtrubrit
What would you usually use the polyester resin for?. It sounds like there's not too much left after skins, bulkheads and sheeting foam. I'm not being a smart a#$, I'm new to this area of the hobby and I'm really curious as I have a can of the poly and was going to use it for foam/wood sheeted wings. Warping and melting seem a possibility.

Keith
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Les


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