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epoxy on epoxy?

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Old 04-12-2008, 08:01 PM
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tazzzz
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Default epoxy on epoxy?

Can you epoxy a piece of wood on top of the already hardened epoxy? Will it adhere, and will it be as strong as normal epoxying. I cant get to the hardened glue,,so i was thinking of epoxying right on top .

TAZZZZ[sm=confused.gif]
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Old 04-14-2008, 01:04 AM
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Default RE: epoxy on epoxy?

You need to rough up the old epoxy for a good bond.
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Old 04-14-2008, 05:30 AM
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da Rock
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Default RE: epoxy on epoxy?

Don''t know if things have changed, but back when epoxy was just getting popular, it was common knowledge that it would bond to either epoxy or polyester resin. And that polyester resin wouldn''t bond to epoxy.

The reason everyone cared about that was that when you were trying to patch something, if it was regular glass or you didn''t know if it was polyester or epoxy, you knew that epoxy would work.

Just some extra info on the topic.............
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Old 04-14-2008, 11:22 AM
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Default RE: epoxy on epoxy?

Epoxy bonds by 2 different mechanisms. Chemically, or mechanically. Most of us rely most of the time on it''s mechanical bonding. It seeps into the surface irregularities, hardens, and then is hard to remove. Chemical bonds happen when new epoxy is added over existing epoxy that has dried partially, but is still tacky.

The chemical bond is the better one, but it''s seldom needed in our work. We encountered it most when fibreglassing a kayak hull, where multiple coats are used to fill the glass fibre cloth over the wooden hull. If we got the next coat going while the first was still tacky, it bonds great. If you have to put the next coat on the next day, it was mandatory to sand the previous coat to provide some "tooth" for the epoxy to hold onto.

Rough''er up!

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Old 04-14-2008, 02:03 PM
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Default RE: epoxy on epoxy?

Just a quick side question, I used 30 min epoxy and glassed the bottom of a high wing plane and it stayed tacky for several days???????? Its in a heated basement, temp in the 60''s and the humity is about normal or just over normal
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Old 04-14-2008, 04:04 PM
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Default RE: epoxy on epoxy?

So without all the scientific stuff,,,If I rough it up ,,,it should be alright......right? thanks-TAZZZZ
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Old 04-14-2008, 06:43 PM
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Default RE: epoxy on epoxy?

Right.

Stick 40,

Your epoxy was either old or your mix ratios were out of balance.
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Old 04-15-2008, 12:36 PM
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Rodney
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Default RE: epoxy on epoxy?


ORIGINAL: Stick 40

Just a quick side question, I used 30 min epoxy and glassed the bottom of a high wing plane and it stayed tacky for several days???????? Its in a heated basement, temp in the 60''''s and the humity is about normal or just over normal
Did you mix it in a plastic or paper cup with a wax coating. I''ve seen two occasions where, when the epoxy was mixed in a waxed paper cup, the epoxy curred poorly if at all. Seems the wax causes problems.
As to epoxy over epoxy, when epoxy cures, it tends to leave a coating on the top that needs to be removed by light sanding and a wash with acetone before trying to add another coat or attachement. Just sand lightly and then wash with acetone or alcohol before attaching anything.
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Old 04-15-2008, 09:38 PM
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Default RE: epoxy on epoxy?

You may be onto something there, I used a small magizne that comes quit ofter. If I used the top page it may have something in or on it. I just bought the epoxy from the hobby store and I mixed it the same way as I always have, I don''t think I measured it that fare off. I am testing another batch before doing the next wing.
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