Polyester resin vs Epoxy Resin

[parnold]

I have been doing a lot of reading, and it seems everyone is using epoxy resin. I plan on painting the finished trailer with hardened automotive acrylic enamel, so the resin I use will have no exposure to the elements. I have used polyester resins on wood on several speaker enclosures I have built (I have two young sons) and never had a delamination issue.
I have access to FREE polyester resin as I sell the stuff and have a vendor willing to supply me, but the epoxy resin will cost me in the area of $65.00 per mixed gallon.
My other question.. to cloth or not to cloth.. just thinking about sanding time here, not really an expense issue.. comments please.

[starleen2]

Ok parnold - I'll Chime in - the last two builds _ i used polyester resin instead of CPES and epoxy. The first was in 3/8 ply and it did real well. The second build I went to a thinner ply, 5mm luan. I fiberglassed All the joints and sealed the whole thing three thin coats of polyester resin. after about a year - it still looks great. My design is Winter Warrior, so the parts get movement every time I set up or take down - and I've camped in both extremes: hot and cold, with not a mention of bubbling or cracking!
Check out the build link below for more details

[Corwin C]

I have used both polyester and epoxy. I personally prefer epoxy (I like how it wets out the fabric, easier to get a proper mix, less fumes when applying, etc.), but either one should work fine.

The build I'm planning will have 4oz fabric because I'll be depending upon the composite structure for strength and durability. If all you are trying to accomplish is a weather tight seal and a smooth surface for paint, you will most likely be fine without the fabric. Just make sure all of your joints and seams are absolutely solid. Any relative motion will eventually crack without the fabric.

[parnold]

Thank you both for your input. I may just use cloth on the seams, I'll have to make that call when I get there based on how solid everything feels. I have an endless supply of sandpaper so time is really the only issue there. Since I am going to try to put a good quality paint job on, cloth on the seams may be prudent.

Scott, the ladybug, although not my taste in decorating, is an awesome build, and so quickly done.

[tk]

Back about ten years ago when I built my canoe, the difference was explained so: Because of the solvents used as thinners in polyester, there are microscopic pinholes that inevitably allow moisture infiltration; not so with epoxy unless you have thinned it. This is why epoxy resin is preferred for higher quality boat construction and for boats that will be continuously in the water and why you should not thin epoxy. If you intend, as you state, to coat with automotive paint, there shouldn't be a problem. Likewise, a polyester-covered boat (or teardrop) that is mostly kept in a garage will probably never delaminate. How accurate this information is I can't be sure.

Best,
Tom

[Dark Horse]

My exp with Polyester and Epoxy resins relate to Auto and boat building.

It was explained to me that Polyester will sit on top of the wood, where as Epoxy will bind with it. In my own informal tests, Western red cedar cut offs. I got a bit of wood to lift when I peeled the cloth up with Epoxy. I had a full covering of wood on the cloth. The poly pulled up some wood, not enough to really resist pulling up. It was informal as I was curious about whether there was any validity to what I was told and I only did one small piece of each.
The Epoxy was system 3, Slow hardener. The poly was Bondo brand I used it for building hidden and flex formed (stretched fleece)speaker boxes.

As to using cloth, it will add weight and cost, but the "high quality" domestic plywood will check even when encapsulated with resin. Adding a layer of glass will help to stop it from occurring

[bve]

Back about ten years ago...

I wonder how much the technology may have evolved since then?

I'll be using epoxy because it is readily available at a local boat builders' supply shop.

[parnold]

The polyester I'll be using will be old technology. I sell newer technology polyesters, but the changes in recent years effect it's adhesion to different types of plastics. Primarily there used to be two kinds of polyesters, those made for SMC's and the "generic". U.S. Chemical has recently introduced a product called All Resin, which is a hybrid.. one number does all product. It's a little pricier than regular polyester resin, but in the automotive collision industry that I am in, it saves a shop money in the long run by not having to keep two separate resins in stock.

There is likely a lot more to the polyester resin story, I'm afraid my knowledge is limited to the automotive industry.

[rpm750]

Glad to see this thread, I'm building an entirely Fiberglass covered exterior. Build design here on this site....
http://www.tnttt.com/viewtopic.php?t=35040

I'm planing on building a frame and covering it with a thin cardboard or construction paper. Cover that with Resin, 10oz Fabric, Resin, 10oz Fabric and finally, Resin and 4oz Fabric. Yes I'll work the fabric into the resin for each layer. I thought about fleece but I'm afraid it will sag when glassing. That's why I'll use the cardboard or construction paper as a support system to produce a level surface, maybe not smooth just level.

Which resin should I use for this type construction?

[parnold]

Polyester resin is what I used when building speaker enclosures using stretched fabric for shape. Experiment some with small scales, and different techniques to see what is possible for you. Also, remember in you figuring, that each gallon of resin weighs approx 10 lbs. If I understand what you're trying to do, you can easily go through 10 gallons.
You're design is certainly possible, and with the right skills will be very solid, and light. I don't pretend to have the knowledge to give you any guidance, but know that lot's of kit car bodies are very lightweight and sturdy, and all they are is fiberglass and resin.

[rpm750]

Thanks man, I'm hoping for both light and strong. This design will have "Studs" per say in the wall construction. About 12" apart or so, I'll use wood around the doors and windows, makes for a better shape. At this point I'm gathering as much knowledge as possible. When I started my Bug rebuild I had never painted a car before, the paint was the easy part now I see all those spots that I missed during prep, door dings, etc.

I'm planning on making a test piece and try different techniques to see which one works and to practice.

Thanks

Bob

[afreegreek]

the two main causes for polyester resin delaminating from wood are

1- impact. polyester resin has a memory and when you impact it it will deform and so will the wood beneath it. the resin will want to return to it's original shape and the wood will not. the stress of this will break the bond between the resin and the wood.

2 - moisture infiltration. polyester resin does allow water to penetrate over time and it will eventually get to the wood or foam or what have you . if it will be dry most of the time and not subject to impacts, polyester is fine on wood..

[afreegreek]

BTW, epoxy is the same it's just a better, stronger bond to begin with and will take more abuse before it delaminates.

[rpm750]

Like I stated in the other post, my plan is to paint it with base and clearcoat once it is finished. I'm hoping that this will give me years of use and I'll keep it covered when it isn't on the road. The whle reason for this type of construction is weight. 3 layers of fabric and 3-4 gallons of resin per side of the trailer should not add that much weight to the total. Yeah it will add to it but not like loan and really nice wood surfaces on the interior.

I'm hijacking this post, not on purpose, if you respond to my post put over here.....
http://www.tnttt.com/viewtopic.php?t=35040

Thanks guys
Bob

[angib]

Nothing wrong with polyester - loads of boats were sheathed in it and lasted decades. Undoubtedly epoxy is better, but I think polyester is good enough. It's a bit like the hardwood/softwood debate - is anyone unwilling to live in a house made from 'just' softwood?

Andrew