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Old Dec 25, 2008, 01:17 AM
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does polyester stick to epoxy?

or the other way around?? I am doin some wing moulds, and would like to make the bottom of the mould absoulutely flat... Can I use bondo on epoxy, for like 1/64"???
Jim
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Old Dec 25, 2008, 01:36 AM
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North vancouver, B.C. Canada
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I bought some special epoxy (g force)that advertised that it will stick to almost anything.
That was not the case.
I tried etching the surface it with plastic cement, stuff that melts plastic, that helped.
drilling holes works
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Old Dec 25, 2008, 06:00 AM
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polyester sticks to epoxy, but epoxy does not stick very well to polyester
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Old Dec 25, 2008, 11:34 AM
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Compatability

I have been able to put thin Bondo on the bottom of my epoxyglass boats to straighten them. It has cured well and never come off, even with the pounding the water gives it, Epoxy will cure and stick well to polyester if you sand the surface curing wax off first. I think a good part of the incompatability myth comes from the old Hobbypoxy Formula II days. Polyester would not cure over Formula II, it would just stay sticky like it wasn't catalyzed. We would have to clean the area up with laquer thinner, lightly smear some 5 min epoxy over the area as a blocking agent, then sand and reapply some polyester resin. A real PITA. After instant glue came out, we could use that as a blocking agent. The epoxies we use now like West and CST don't seem to do this. All that being said, I still try to put epoxy on epoxy and polyester on polyester. The new catalyzed spot putties feather edge better than Bondo, but are harder and more difficult to sand. Rudy
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Old Dec 25, 2008, 12:46 PM
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Awesome.. Thanks guys!
Jim
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Old Dec 25, 2008, 05:00 PM
Will fly for food
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Polyester still doesn't stick well to epoxy. It may cure fine, but there is very little bond strength between the two. Epoxy sticks great to polyester.

Finishing polyester resin has wax. That wax layer needs to be removed before using epoxy, first with a solvent wipe, then with sanding. If you sand first, you can drive the wax intot eh surface of the polyester and the sanding scratches, reducing the strength of the bond.

I repair my full scale race car all the time using WEST epoxy onto the polyester/fiberglass parts. I have never had a bond break. But the Bondo for fairing will just pop off in large sections. And yes, the epoxy was sanded first.
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Old Dec 26, 2008, 02:03 PM
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Many people, myself included, use bondo to make wing and stab fillets on one-piece epoxy slope planes. These planes take a beating. And I use bondo all the time for filling in minor nicks and scratches on those planes. By the time you sand it to fair it in, the bondo usually isn't very thick, but still I've never had a piece come off.
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Old Jan 06, 2009, 02:56 AM
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If you're going to bond epoxy to polyester glass, sand the area first with 40-grit sandpaper (finer for thinner surfaces). Epoxy forms a mechanical bond. So the more "teeth" you provide, the better the bond.

As mentioned, West Systems works great. Get the measuring pumps. It's about $10 but worth the price since it makes the measurement task a breeze. And if you're going to use more than a quart, buy a gallon. Surprisingly enough, it's way cheaper that way.

Don't disturb the joint until the epoxy it's fully cured. Set aside a sample and check the sample to see if it's cured. Epoxy generally takes a few days to reach full strength.

Conversely, if you wax a surface, epoxy pops right off. It's what I did when I "glass bedded" my rifle, and made tapered mounts for my boats bimini top.

If you apply polyester to epoxy, you could end up softening the epoxy. The solvents used in polyester resin can dissolve cured epoxy resin.
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Old Jan 06, 2009, 11:04 AM
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Quote:
Originally Posted by Windbreaker
If you're going to bond epoxy to polyester glass, sand the area first with 40-grit sandpaper (finer for thinner surfaces). Epoxy forms a mechanical bond. So the more "teeth" you provide, the better the bond.

As mentioned, West Systems works great. Get the measuring pumps. It's about $10 but worth the price since it makes the measurement task a breeze. And if you're going to use more than a quart, buy a gallon. Surprisingly enough, it's way cheaper that way.

Don't disturb the joint until the epoxy it's fully cured. Set aside a sample and check the sample to see if it's cured. Epoxy generally takes a few days to reach full strength.

Conversely, if you wax a surface, epoxy pops right off. It's what I did when I "glass bedded" my rifle, and made tapered mounts for my boats bimini top.

If you apply polyester to epoxy, you could end up softening the epoxy. The solvents used in polyester resin can dissolve cured epoxy resin.
Lol... "by the gallon"... Funny how that used to be a lot, huh?? I just want to make my moulds sit absolutely flat on my layup board, and while post curing. Bondo is cheap, and so am I at this point. I am using Evercoat, so it does cost a little, but it seems to stick great. One of these days I need to make a CNc... this whole sanding for 50 hours thing is getting old!
Jim
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Old Jan 09, 2009, 01:41 AM
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I'm doing a story about a boat builder, and he makes all sorts of molds. The usual plug material includes masonite, medium density fiberboard, bondo and black gel coat. Black shows up imperfections really well, which is why shiny black cars are such a pain to keep pristine.

And, yes, there's a lot of sanding and polishing involved.

From the plug he makes the mold, and that's out of several layers of fiberglass, usually reinforced with lots of plywood. Sometimes steel tubing is used. And the inside of that is glass-smooth, as was the plug.

Looks like a simple process but it's painstaking. It involves a lot of man-hours and it's a very small shop. So if someone asks for a custom addition, he now requires the customer to pay for a portion of fabricating the mold, even though the piece is later added to the production options.
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