[ctbecker]

Getting to the fiberglass on my 8A. Dont understand the difference between polyester and epoxy. What are the differences, strengths and weaknesses of each?

Charlie Becker
N464CB RV8A(ES)
Finishing Kit has arrived!!

 

[flyeyes]

Short answer--you need to use epoxy for the stuff you'll do on the -8A.

Don't use the stuff from Lowe's or Home Depot. Get some West System (google it, there's tons of information on their site) epoxy and the ratio pumps.

If possible, get a local plastic airplane builder to show you the basics--it's very easy but not entirely obvious at first.

Read the labels, try to keep the stuff off your skin and especially out of your eyes.

James Freeman

 

[jcoloccia]

Getting to the fiberglass on my 8A. Dont understand the difference between polyester and epoxy. What are the differences, strengths and weaknesses of each?

Charlie Becker
N464CB RV8A(ES)
Finishing Kit has arrived!!

This almost belongs under "neverending debates"

My personal opinion is that polyester really doesn't have any advantages over epoxy in the quantities that we're using them in. It's a fraction of the price of epoxy so if you're mass producing fiberglass hulls, for example, it's significantly cheaper to do the layup with polyester rather than epoxy. Done properly, with the proper conditions and timing between layers, you end up with a good product. Those boys have it down to a science and are able to consistently achieve chemical bonding between various layers of polyester layups.

Epoxy is excellent at forming mechanical bonds to just about anything (superior to polyester on dang near everything). This is important for us because we get everything long after it's cured....we can't depend on the chemical bond. It also sands really well. We're not using enough epoxy that cost is at all factor.

IMHO, it's easier to work with epoxy, especially using West Systems ratio pumps....a couple pumps of this, a couple pumps of that and done. With polyester, you're counting little drops of MEK. Ever see polyester resin with a few too many drops of MEK in it? It's quite exciting to watch. Really not THAT bad, though.

The plane won't fall out of the sky using polyester...we're just filling in pin holes, smoothing transitions, closing up the occasional tip, etc etc etc. You could probably use gorilla glue and spackle if you really wanted to (just kidding...don't really do this ). You get the point, though...either will work. Personally, I think epoxy is just easier to work with and has superior properties. It's also compatible with just about everything out there.

Just one mans opinion

 

[Mel]

A few things to remember about polyester and epoxy. They are very different.
1..Polyester never completely cures. It continues to shrink forever.
Look closely at a 40 year old Corvette. You can see the seams in the body.
Look at the cowling and wingtips on a 13 year old RV-6. You can see the
weave in the fiberglas. You could not when I finished it in 1993.
2..Polyester does not adhere well to epoxy. When I built my Dragonfly, I used
polyester to "glue" temporary alignment blocks because they could be easily
removed.
3..Never use polyester in direct contact with plexiglas. It will attack it.

 

[Dgamble]

A little bit of a thread hijack, but I've been meaning to ask for a couple of days and this reminded me:

I'm replacing my old wheel pants and fairings with Vans pressure recovery pants and F1 Rocket leg/intersection fairings.

Working on the pants just now, and I see that I will be expected to lay up some cloth to provide "shims" and additional strength. Having noted earlier in the thread that the aviation dept. at Lowes does not have what I need, and being not too far from a marine shop that reportedly stocks West Systems products, it would be reasonably convenient to get the products I need. The only remaining problem is:

I don't know what products I need.

Could someone that has been down this path provide a shopping list?

 

[Highflight]

One more thing to add to the obvious ones given is that epoxy is more resilient (flexible, but not as in "rubbery". More like "not brittle") compared to polyester.

Epoxy handles vibration and impact stresses much better than polyester, so if you want to install something as permanent as practical, use epoxy.

Talking about Corvettes... I was in the Corvette repair business for over 25 years, and dealing with stress cracks was one of the biggest headaches we had to deal with because Corvettes were made of polyester based resins since '53.
It wasn't until '84 when they started using SMC resin body parts that stress cracks became less of an issue even though SMC is still a polyester based resin (a bit of a hybrid). Then the headaches got worse because standard saturated polyester couldn't be used to repair it because of compatibility issues. It was a real nightmare until I finally found what did work to repair SMC, and at the time, even the local Chevy dealers didn't know what to do and even they got no help from Chevrolet.

Thank you for letting me get that off my chest.

The short story is that epoxy resin for the critical layups is the only way to go.

 

[RV_7A]

Also Polyester resin is flammable as all get out before and after it cures. Epoxy is not.

 

[mdredmond]

it would be reasonably convenient to get the products I need. The only remaining problem is:

I don't know what products I need.

Could someone that has been down this path provide a shopping list?

I haven't been down that exact path, but have used West products extensively on my sailboat.

At a minimum you'll need:

West 105-x Epoxy
West 205-x (Fast) or 206-x (Slow) Hardener
West 300 Pump Set
Appropriate cloth

The -x refers to the 'group size'. Make sure your cans of epoxy and hardener have the same group size (the products aren't mixed 1:1 so the hardener can will be smaller than the epoxy can).

The above is fine for doing cloth layups. If you are going to be fairing or filling, get some 407 or 410 filler. You add this to the mixed epoxy to make a peanut-butter-like mess that you schmooey on and sand down.

 

[RV_7A]

Just wanted to ask if anyone has had a chance to use MAS Epoxy yet. I went through a gallon of West Systems already and then bought some MAS. I am very impressed with this product. It has a slightly lower viscosity and dries very hard and a bit shinier. It is mixed 2:1 and the pumps work great. They don?t drip. Also it was about $10 cheaper than a quart of West. Anyone else used it and have any feedback? West Systems has been around forever but MAS seems to be the "newer technology" epoxy IMO. I doubt I will ever use West Systems again.

-Jeff

 

[MSFT-1]

Newbie question

After busting up one of my wheel pants last December, I am finally getting around to getting it fixed. I bought the new front and back halves from Van's. The local airport fiberglass guy looked at it and said the parts are polyester. He really "seems" to know what he is talking about.

Since he is going to build this for me, should I specifically ask him to use epoxy for this project?

thanks,

bruce
N297NW

 

[Dgamble]

Perfect! Found it all just up the street at the landlocked marine shop. Stuff ain't cheap, though.

Thanks for the help.

I haven't been down that exact path, but have used West products extensively on my sailboat.

At a minimum you'll need:

West 105-x Epoxy
West 205-x (Fast) or 206-x (Slow) Hardener
West 300 Pump Set
Appropriate cloth

The -x refers to the 'group size'. Make sure your cans of epoxy and hardener have the same group size (the products aren't mixed 1:1 so the hardener can will be smaller than the epoxy can).

The above is fine for doing cloth layups. If you are going to be fairing or filling, get some 407 or 410 filler. You add this to the mixed epoxy to make a peanut-butter-like mess that you schmooey on and sand down.