PDA

View Full Version : Epoxy vs. Polyester ?



jg480
09-02-2009, 08:24 PM
I know this is going to open up a can of worms and that is not my intent. I have been reading some post over on Scream and Fly about resins trying to get a little more educated before diving into the St. Tropez. I know epoxy has stronger secondary bonding characteristics than poly or vinyl, but is it really necessary? I need to replace pretty much everything, all the coring, transom and probably stringers. I really don't want to spend $2000 on epoxy for structural repairs if it is not needed. I will use epoxy for fairing and cosmetic work do to it's low shrinkage. I have used poly on several other boats with no problems but this one is going to be special so I want to do it right!
Jim

gcarter
09-02-2009, 08:45 PM
A few basic rules;
You can apply epoxy over poly
You CAN'T apply poly over epoxy.
You can't paint over epoxy (not easily anyway)
You can use vinylester resin and get much of the strength of epoxy for less than the cost of epoxy.

Does that help?

MOP
09-02-2009, 09:06 PM
I have found standard resins to do a good job, any place I feel extra strength is needed I just add another layer or two, one place not to use epoxy is below the water line, some will argue that point but I have tried several and they all white out over time indicating moisture absorbs ion. I always make sure I have what I call a good tooth meaning slightly rough but very clean surface. There is a resin that etches the glass for a better bond, I have never used it but it is worth looking into for higher stress areas. Two mistakes most make when doing structural repairs in not isolating various wood pieces from each other. If for instance the transom gets wet it will wick into the stringers! Another big one I learned from my glass guy is not to continue the transom wood all the way down to the bottom of the bilge, when the work on mine was done the lower edge of the transom wood was cut flat with no V, in stead glass was laid in the bottom to a thickness of 3/4 inch to mount the drain. 90+% of transom rot starts from the drain plug no matter how good a sealing job is done, by eliminating the wood you eliminate the problem. There is -0- benefit to putting the wood all the way down just liability!

More debate to follow!!

axelkloehn
09-03-2009, 02:16 AM
Some experiences I have made:

Epoxy needs more time to dry, that means you can work fantastic wet-in-wet up to an hour or so. But when you apply it on vertical or negative angled surfaces it flows to the ground, even under the glassfiber which can result in de-laminating. Working overhead is almost impossible, it drops everywhere...
Polyester has a shorter drying period and stays better on vertical surfaces because it's thicker and you can control the working time with the amount of hardener in it.
Epoxy strictly needs a certain amount of hardener, otherwise it will loose its qualities. And it needs at least 24h to dry completely, you have to wait before you continue working. And it remains sticky for a long time, every thing which is around sticks on it, could be annoying when you sit on an edge you put epoxy on an hour ago ;-)
But the quality and stiffness is outstanding, it's perfect for stringers and transom work- you aply it, forget about it for a day and it's stiff like hell.

I use polyester/fiberglass for finishing purposes or filling up- short drying periods save a lot time- and of course no use on underwater surfaces...And Polyester is about 1/5 the price of Epoxy.

Cheers, Axel :germany:

David Ochs
09-03-2009, 08:34 AM
I used epoxy exclusively when restoring my '69. Wonderful to work with and had fantastic results. However, after a couple of years I began to notice some movement in the fairing work on different areas of the deck.
What was once perfect is now not. Everything has remained well bonded, even after some 15 years.
I spoke with a technician from West System about this, and he suggested that heat from the sun can soften the epoxy when polyester is unaffected.
Keep in mind that my boat still looks awesome, people tell me that I am the only one that sees what I am describing. Most likely because I am the one that spent countless hours with the sanding block in hand!

Dave

LKSD
09-03-2009, 09:05 AM
A few basic rules;
You can apply epoxy over poly
You CAN'T apply poly over epoxy.
You can't paint over epoxy (not easily anyway)
You can use vinylester resin and get much of the strength of epoxy for less than the cost of epoxy.

Does that help?

Actually you can apply paint over epoxy & it isnt that bad hard to do, but it must be prepped & cleaned properly.. ;) Otherwise the usual Amine blush leaves a waxy residue that will caues adhesion issues. You can also post cure the epoxy, but most places or individuals dont have the capability to do that.. ;) Jamie

gcarter
09-03-2009, 09:20 AM
You're right jamie.
In fact System Three Epoxy has a whole series of paints that can be applied over epoxy.

axelkloehn
09-03-2009, 02:55 PM
Actually you can apply paint over epoxy & it isnt that bad hard to do, but it must be prepped & cleaned properly.. ;) Otherwise the usual Amine blush leaves a waxy residue that will caues adhesion issues. You can also post cure the epoxy, but most places or individuals dont have the capability to do that.. ;) Jamie

George, what's the risk with poly over epoxy- did it several times and never had problems- two or three layers glass with epoxy, then a few layers thicker glass with poly for filling up, and again fine glass/epoxy for the final stiff surface, putty+filler and paint, worked good. What can happen? Did my GT in the same way and am a bit worried right now....

gcarter
09-03-2009, 03:09 PM
George, what's the risk with poly over epoxy- did it several times and never had problems- two or three layers glass with epoxy, then a few layers thicker glass with poly for filling up, and again fine glass/epoxy for the final stiff surface, putty+filler and paint, worked good. What can happen? Did my GT in the same way and am a bit worried right now....

Axel, go here;
http://www.systemthree.com/index_2.asp
and download their book.
It'll explain everything.

gcarter
09-03-2009, 03:15 PM
I used epoxy exclusively when restoring my '69. Wonderful to work with and had fantastic results. However, after a couple of years I began to notice some movement in the fairing work on different areas of the deck.
What was once perfect is now not. Everything has remained well bonded, even after some 15 years.
I spoke with a technician from West System about this, and he suggested that heat from the sun can soften the epoxy when polyester is unaffected.
Keep in mind that my boat still looks awesome, people tell me that I am the only one that sees what I am describing. Most likely because I am the one that spent countless hours with the sanding block in hand!

Dave
Heat is a problem w/epoxy. It will soften in the sun and harden again.
It also has to be protected from the sun.

axelkloehn
09-03-2009, 03:29 PM
Axel, go here;
http://www.systemthree.com/index_2.asp
and download their book.
It'll explain everything.

...done, will be my good-night-reading matter tonight. Thanks George, that teaches me a lesson, hope the debonding will not ruin my project :eek:

jg480
09-03-2009, 03:31 PM
What if I use epoxy to "glue" in the coring and transom being careful not to let the epoxy extend beyond the core. Then add the following laminates using a vinyl resin. I am mainly concerned with delamination of the coring, transom or stringers.
Jim

LKSD
09-03-2009, 07:44 PM
The epoxy is usually affected by mek & other hardeners used in Vinylester & Polyester resins when applied over epoxy. :) Jamie

mike o
09-03-2009, 08:16 PM
All ya need for this project is a high quailty isothalic polyester resin (the good stuff) without any wax in the resin. :yes:

HOWARD O
09-04-2009, 08:45 AM
I used epoxy exclusively when restoring my '69. Wonderful to work with and had fantastic results. However, after a couple of years I began to notice some movement in the fairing work on different areas of the deck.
What was once perfect is now not. Everything has remained well bonded, even after some 15 years.
I spoke with a technician from West System about this, and he suggested that heat from the sun can soften the epoxy when polyester is unaffected.
Keep in mind that my boat still looks awesome, people tell me that I am the only one that sees what I am describing. Most likely because I am the one that spent countless hours with the sanding block in hand!
Dave

Hey, how's about posting some nice photos of that trailer queen for us? :yes:

realbold
09-04-2009, 09:24 AM
I'm using epoxy. Poly/vinyl makes a poor secondary bond. Paint is no problem with epoxy primers and urethane as long as you sand the shine off first. And System 3 Silvertip resin leaves no amine blush. Never use 1 part alkyd enamel on epoxy. Never use mat with epoxy. Mat backed biax is ok if it says it is epoxy compatible.

David Ochs
09-04-2009, 10:51 AM
Hey, how's about posting some nice photos of that trailer queen for us? :yes:
Done, one anyway

CHACHI
09-04-2009, 11:52 AM
Thanks. Sweet.

Ken

HOWARD O
09-04-2009, 12:35 PM
Done, one anyway

That's one I hadn't seen. I think you need to load up some photos to your photo gallery! Maybe some resto. photos if you can find them. Any photos I had were on my stolen laptop computer, not backed up of course. :cool:

RickR
09-05-2009, 03:27 AM
www.uscomposites.com

rustnrot
09-05-2009, 08:47 AM
After awhile we all get "set" :wink: in our ways. For me, it is always using epoxy and always using paint (not gel coat).

If I had to do it any other way (poly--the stink alone would run me out of the neighborhood and probably kill our parrots in the house) -- or be forced to re-gel a hull (my hat is off to those of you with the skill and patience to do this), I would pick another hobby.

I have used stuff from uscomposites for years. Go with the Medium set laminating epoxy, even here in hot GA the pot life is sufficient.

RBT
09-06-2009, 11:22 AM
A few points.

- Epoxy only reaches its strength when post cured.
- Epoxy IS waterproof
- Vinylester IS waterproof
- Polyester is NOT waterproof
- A good Vinyl like Dow Durakane has mechanical bonding as good as epoxy at half the price. Add that it can be covered with cheaper poly. Epoxy has bonding issues with paint and gel. Not impossible but a pain in the but.... Not worth it.
- You only need vinyl for your first layer, to great a decent mechanical bond to the old hard poly. After that you can use poly as long as you keep it within 18 hours, you will get a chemical bond

RT