Epoxy Resin

[73383]

About to get started on the fiberglass work on the 73. I have a front end to hang and a rear tail panel to install. Has anyone had any experience with epoxy resin and epoxy bonding adhesive, versus the polyester resins and bonding adhesives.
Good stuff? Bad stuff?
I've heard it's 4 times stronger than polyester but harder to work.

Dennis

 

[Twin_Turbo]

Okay, I'm in the same boat but need to use epoxy on my rear clip since it's a late car with smc panels.

Epoxy is stronger but there's a catch.

On a vette you use chopped strands matte since the woven cloth will show through the paint (unless you're using it on a part that doesn't show but needs strength, woven matte is stronger than chopped strands matte)

Here's the catch:

You can use epoxy on the woven stuff and it will come out fine, you can't on the chopped strands matte. Why? Chopped strands matte needs to crosslink in the matrix to get the desired strength and for this you need styrene, the problem is, epoxy resin doesn't have any styrene in it, polyester does, that's why you don't use epoxy with chopped strands matte.

Now since vettes are to be repaired with chopped strands matte and the general decided to use SMC we have a problem, polyester doesn't stick to smc all that well and epoxy can't be used with the correct matte. Now Ecklers sells a special laminating resin for SMC wich is epoxy and can be used with crushed fibers. I think they mixed styrene into it but don't know for sure. I emailed Adtech who makes the resin Ecklers sells but they haven't replied to my email (and they probably won't as most companies don't know what customer service means nowadays). I can't get the stuff here since they won't ship hazardous materials overseas.

Epoxy isn't harder to work with, you just have to be a bit more precise measuring the ingredients.

If I were you I'd use normal polyester resin and chopped strands matte, it's a proven method, no need to get fancy (plus expensive, epoxy is more expensive too)

I hope Chris is reading this so maybe he can give some insight on this subject. I've asked on another forum and sadly I don't think anyone there knows, they just say get the Ecklers stuff, I would if I could.

Also since the subject was brought up, is there anyone who has used epoxy resin and micro balloons to make their own filler?????
I seriously dislike most of the commercially available filler, most are too grainy, come off easily or harden waaaay too fast s so if someone has had good results with micro balloons I may be tempted to use that

Marck

 

[73383]

Marck

Well, I'll let you know how it works. Today I ordered Eckler's resin and bonding adhesive. I talked with a boat repair guy today. He says epoxy is five times stronger than polyester. I worked in a Vette body shop in early 1980s and always used Ecklers bonding adhesives. Always had good luck with there products.

Dennis

 

[Twin_Turbo]

I'm overseas and the ecklers (AdTech) stuff can't be shipped by air

 

[Dood1]

Here's some more info on Epoxy and polyester resins from my experience in boat repair.

Polyester resin uses peroxide catalysts, (either MEKP or BPO), to initiate the chemical reaction that causes them to harden. Epoxy is a two part chemical that uses exact amounts of each part to cross-link to the other part, usually in a ratio of 5-1 or 4-1. Epoxy doesn't work with chopped strand mat because the mat has binders which will only dissolve with the polyester resin.

The problem with seeing the weave, ("print through"), when you use woven cloth is that there is some shrinkage with poyester resin when it cures, so what looks like a smooth surface will often show the surface of the fabric underneath after it cures. This can usually be prevented by another application of resin or filler, and is less of a problem with finer weaves of cloth.

Epoxy shrinks less upon curing, so print through is less of a problem, and again can be eliminated by sanding and then applying more resin and filler.

Do not use a polyester based filler over epoxy resin.

Epoxy is a harder product and therefore a little more difficult to sand. Since you can't get the proper SMC resin, I think you will be able to do a fine job using Epoxy resins and fillers. It may take a little more work, but in the end the repair will be stronger. Hope this helps.

 

[Dood1]

Also, if it's not too large an area, you can make your own chopped strand mat. Just take some woven fabric, the heavy woven roving is good, un-weave some strands, and cut them up into small pieces with scissors. Saturate them with mixed epoxy and you've made a strong, fiber reinforced putty.

 

[Twin_Turbo]

the last thing you mention is what I always do to create filler, it gives a nice thoick paste that can fill large holes quickly. I need the stuff to bond fender flares to the SMC panels, I guess I'm gonna use epoxy and the woven cloth. Here's the finest cloth I have, I think it will do fine then.

 

[Dood1]

It's hard to tell exactly from the picture, but that looks like 6 or 10 ounce cloth, which should be fine. Another thing you can do to minimize print through is to post-cure your patch with a heat lamp or heat gun. Don't get it too hot, but take it hotter than it will get on a hot summer day in the sun. Much print through occurs after a boat is pulled from the mold and heats up in the sun, especially with darker gel coats, which is one reason you don't see too many boats with dark colored hulls. Again, this is less of a problem with epoxy resins than polyester, but applying a little bit of heat is an easy safety measure. Good luck with your repair.

 

[73383]

The bonding adhesive got here today, fast, I just ordered it yesterday. Ecklers also carries an epoxy based body filler, which I ordered. The resin a body filler are still in shipping. I ordered the hood surround, fender and bumper about a week ago. They should get here soon.

I spoke with a boat repair guy also. He says you can use chopped mat with epoxy, you just have to work it harder to get it wet?? I am very hesitant to use cloth. In the 70s and 80s I repaired many Vettes that someone had repaired with cloth and the patern came through. My 73 I am working on now had several spots repaired with cloth and you could see all of them before I stripped the paint.

However that was some cool looking cloth. I have never seen any like it. What is it called? I may have to try some.

 

[Twin_Turbo]

I use fibers to thicken my epoxy, you can make your own filler that way. Very easy. The same epoxy can be used for laminating, indeed it's harder to saturate the cloth but it's not that hard.

I just did my front (I'm building a clamshell hood) and am almost done, just a small section of it needs laminating, some grinding.. filling and then the finishing touch:

 

[Dood1]

I spoke with a boat repair guy also. He says you can use chopped mat with epoxy, you just have to work it harder to get it wet?? I am very hesitant to use cloth. In the 70s and 80s I repaired many Vettes that someone had repaired with cloth and the patern came through. My 73 I am working on now had several spots repaired with cloth and you could see all of them before I stripped the paint.

However that was some cool looking cloth. I have never seen any like it. What is it called? I may have to try some.

Do NOT use mat with epoxy. It may look as if it's working, but as I said above the binders in the cloth are not compatible with epoxy resin and it will not cure to full strength.
The patches with cloth that are visible were probably done with polyester resin, if you follow my suggestions you will not have print-through with epoxy. I repaired a badly damaged metal fender on a Supra with epoxy and cloth, and painted it black, and never had any print through. The key is to sand between coats and get enough resin and filler on top of the cloth.

 

[Dood1]

I use fibers to thicken my epoxy, you can make your own filler that way. Very easy. The same epoxy can be used for laminating, indeed it's harder to saturate the cloth but it's not that hard.

Just to be clear, chopped fibers are a good structural filler, but not great as a sanding/finishing filler. You want something finer, like colloidal sillica or microballoons, which are easier to sand as well.

 

[Twin_Turbo]

That's the stuff I mean, microballoons and fibers (they come pre mixed in a can or seperate) The mxi stuff gas good filling capabilities, good strength and still sands out smooth.

I turned to West Systems stuff, we'll see how it turns out (they had the epoxy and microballoons & fibers so i could mix to desired consistency and thickness, the other stuff came as a thick paste)

As for epoxy, here's what you get when you use it (this was done on purpose to show people on another forum what happens, it's an old hood)

The patch looks like it's cured properly but when you attack it with a sander or something you will see you can tear the fubers out, there's no cross linking there, it's just loose fibers surrounded by epoxy resin.

The stuff I'm using now is the brown goop in this pic, the brown is from the microballoons & fibers, the stuff itself is clear.

 

[Dood1]

Yeah, West System has good stuff.
They also have a 410 Microlight filler that makes a nice finishing filler.
One thing I have found with the West system, sometimes the pumps they supply get air bubbles in them or don't pump well if the temperature is low, which can mess up the mix ratio a little. I use paper cups marked off with the 5 - 1 ratio and measure by volume to mix my smaller batches.

 

[Twin_Turbo]

That's why I don't use the pumps, they're pretty useless anyway since some manufactureres state volumetric mix ratios where others use weight ratios. I use clear cups, just pour in 5 cm of resin and add another cm of hardener, mix, let air bubbles come out, toss in desired amount of filler and mix again, let it sit a little while (about 5 minutes or so) and apply. Gelling time is about 20 minutes, 15 when warm like it is now.

The filler I use now is 407

Marck

 

[Dood1]

As for epoxy, here's what you get when you use it (this was done on purpose to show people on another forum what happens, it's an old hood)

Just to avoid confusion for others, this is what happens when you use epoxy resin and fiberglass MAT
That's a very good example of why you don't use mat with epoxy.

 

[Dood1]

Gelling time is about 20 minutes, 15 when warm like it is now.

The filler I use now is 407

Marck

Ever mix up a batch in the heat and have it smoke and harden up before you can use it? Fun stuff :L

 

[Twin_Turbo]

Just yesterday, was pretty fun to watch, untill I thought about how much $$$ worth of epoxy I saw smoking away

Made a pretty nice cup shaped blob of goo though, may come in handy sometime for some sillyness

 

[arrio]

I've worked with epoxy resins a good bit (West Systems Epoxy) fabricating model fuselage components for radio control models. I found that if you leave the mixed resin in its mixing cup, it will tend to exotherm much quicker than if it was spread out on the work piece. When sitting in the cup/container heat realy builds up quickly and then the whole batch cooks off in smoking frothing mess. More so in warmer anbient temperatures. Resin setting time is cut nearly in half when the batch is left in it mixing cup. Try to spread out the resin as soon as possible. You will then likely have the full advertized working time.

 

[Dood1]

If I need extra time, I often will put the resin in a shallow plastic pan so it can spread out, or even put it in the fridge for a bit.