Polyurethane Resin vs Epoxy

[synaps3]

I can get a gallon of this:

polyurethane resin

for less than the price of a quart of this:

epoxy.

What makes epoxy so much more expensive, and why should I use it over poly resin? Poly resin seems to do the exact same job to me...

Thanks,

[starleen2]

The debate continues!
I have used resin on the ladybug - others use epoxy - they both have merit and drawbacks. I guess it all boils down to preference and experience with both products. see the below links for threads that have discussed this

Ok - 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

http://www.tnttt.com/viewtopic.php?t=35240&highlight=epoxy+resin

http://www.tnttt.com/viewtopic.php?t=34039&highlight=epoxy+resin

http://www.tnttt.com/viewtopic.php?t=31278&highlight=epoxy+resin

http://www.tnttt.com/viewtopic.php?t=25276&highlight=epoxy+resin

[CPlater]

Polyester does not bond as well as epoxy to plywood and is generally less water resistant and not as flexible. Poly does not bond well to epoxy so if you use CPES sealer you will not be happy with the results if poly is used over it. If you choose polyester resin be sure to rough up any surfaces to create a better bond.

[BigAl]

Hi Dave, I cannot speak for the Polyurethane but Epoxy is superior to Polyester. Don't take my word for it.

From a boatbuilding site that I use.

"Can I use polyester instead of epoxy?

No. If the plans specify epoxy, you should use that resin. Polyester does not bond properly to plywood and will delaminate.

What kind of resin should I use?

All our plans specify epoxy resin exclusively. Polyester or vinylester are not acceptable. Polyester does not bond properly to wood and is not sufficiently resistant to moisture. With polyester, water will find it?s way to the plywood and result in rot, not with epoxy. Use a quality marine epoxy like the one we sell in our kit: it does not cost more.

What is the shelf life of epoxy resin?

Epoxy has an almost unlimited shelf life. You can keep epoxy for years and it will be as good as the first day. In very cold weather, epoxy may crystallize. It will become liquid and clear after warming up and will have exactly the same properties. "

I would also like to add that your ply NEEDS to be totally dry to get a good bond with Polyester. Do you know the humidity of your ply?

I have plenty of Polyester in the shed, but just had to spend about $120 to get Epoxy for my trailer. There isn't any point in saving a few $$$ just to spend it all later trying to fix the trailer. I've never come across West Epoxy here in the UK, but I have seen it get a lot of praise in the boat building community.

[synaps3]

Scott --

What type of paint did you use on the ladybug?

I'm anticipating using aluminum for the roof of my build, but painting the sides. I would like a relatively shiny finish on the sides... Does auto paint stick to poly resin?

Courtney --

That's what I've read... But my build is 13'6" long, 7' tall, and 7' wide. Buying $500 dollars worth of epoxy resin vs buying $100 of poly resin for what seems to be the same result seems silly to me.

I'll be fiberglassing all edges to mitigate moisture intrusion.

I'll definitely roughen up the surfaces. Thanks for the tip.

Al --

I'm using luaun, so even if I go with "real" epoxy, the luaun itself is probably more likely to delaminate from itself before the epoxy delaminate from the surfaces.

The humidity does raise concerns though. It is really humid here...

[starleen2]

I used regular enamel house paint - read the key word "enamel". I also use 5mm luan for both the inside and the outside.

Hummmmm - it seems that they build boats out of fiberglass and use polyester resin for the bonding and gel coat - they built corvettes using resin - you'd think that if epoxy was that superior they'd be using it instead. There are plenty of boats and Kayaks built years before and after epoxy that are still in the water

[Jst83]

synaps3, how are you planning on finishing you camper? Mines 6'6"x11'6" so i understand what you mean by taking a lot to finish. All I did on mine was seal the seams and edges with the poly and tape then painted it with a good oil exterior primmer followed up by a couple coats of good exterior latex. I've had no problems in 2 summers. Gonna repaint this summer just cause I wanna different color

Mine does live indoors when I'm not camping so these results may vary if stored outside.

[synaps3]

I might end up storing it outside next year. Our lease on our apartment expires in October, and I've got enough saved to put down a down-payment on a small house. With the way the economy is, a 15-year mortgage around here is actually cheaper than renting.

That said, I decided that I don't want a painted roof. It needs to be something that will continually stand up to the weather, even if I store outside. I considered FRP, but that crap is a fortune! Plus, I am going to require that the whole top and front be one contiguous piece for the best waterproofing.

My roof and front will be one contiguous piece of 0.40mil aluminum, about 6'8.5" wide and 20' long. Underneath will be a couple layers of poly resin.

All seams will be glassed using poly resin. Voids and cracks will get filled with bondo.

Walls will get poly resin, and either durabak as the final coat, or possibly some sort of automotive enamel paint. An exterior latex will work, but probably won't be as shiny as I want this trailer to be.

[Jst83]

Voids and cracks will get filled with bondo.

Careful of the auto bondo I filled my seams with it then after a 16 hr trip and back it started to crack real bad I had to strip all me seams and redo them. might not have cracked so bad if I'd have put resin and tape over the bondo. Just ones mans issue with bonbo

[starleen2]

Like Scott said on the seams - fiberglass resin and fiberglass tape on the SEAMS first! then sand and Cover with Bondo to make for a sharp edge or smooth transition

[afreegreek]

first you have to be more specific.. use this over that for what?? anyway, those boat building sites are a good source of info but not all of it applies to building your trailer.. they say to use epoxy over polyester resin because the strength of the canoe/kayak depends on the glass resin combo. not so with your trailer. for it you're wanting it as a sealer more than anything else. if you use polyester resin on good dry wood you won't have any problems.

[parnold]

Polyester resin is not 100% waterproof, which is a big reason boat places say not to use it. I plan on using polyester resin because I am going to paint my trailer with a quality automotive acrylic enamel. This will provide the 100% waterproofing that I need, as well as excellent uv protection.
I have made several speaker enclosures with polyester resin over wood, I have two teenage sons with stereo systems you can hear half a mile away. All that vibration and I have never had a delamination problem. I would suspect most delamination problems are really created by faulty installation such as laying the glass and trying to soak the resin through it instead of applying the glass over an existing wet surface, or not allowing the first coat enough time to cure/dry, thereby trapping solvents in the lower coat.
I will admit that I have only applied polyester resin over mdf and plywood, never over luan or hardwoods, so my current build may be a learning experience for me.

[afreegreek]

Polyester resin is not 100% waterproof, which is a big reason boat places say not to use it. I plan on using polyester resin because I am going to paint my trailer with a quality automotive acrylic enamel. This will provide the 100% waterproofing that I need, as well as excellent uv protection.
I have made several speaker enclosures with polyester resin over wood, I have two teenage sons with stereo systems you can hear half a mile away. All that vibration and I have never had a delamination problem. I would suspect most delamination problems are really created by faulty installation such as laying the glass and trying to soak the resin through it instead of applying the glass over an existing wet surface, or not allowing the first coat enough time to cure/dry, thereby trapping solvents in the lower coat.
I will admit that I have only applied polyester resin over mdf and plywood, never over luan or hardwoods, so my current build may be a learning experience for me.

most delamination starts from an impact and grows over time from successive warm cool cycles.

[parnold]

Your not supposed to hit your trailer are ya>

I suspect that it is similar then in how paint comes off plastic bumpers, I'll cross my fingers then for my build.

[afreegreek]

BTW, epoxy is not 100% water proof. it is a lot better than polyester but water molecules can still pass through it. think of it this way... most resins are made up of chains of molecules like threads and are criss crossing each other and bonding to each other where they touch forming what looks like a solid surface but it is not, it's more like a piece of cloth with little gaps between the threads. a water molecule is only one hydrogen atom and two oxygen atoms. that's pretty damn small and will pass through the gaps between the threads/chains of resin molecules.