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Old Apr 22, 2012, 10:59 PM
Mustang MadMan is offline
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Question

Two part epoxy and styro-foam


Hi, I have a flyzone cessna 182 skylane and was wondering if the two-part epoxy found at your local Walmart is to agreesive. I need to re-secure my engine mount - mount which is metal to the styrofoam.

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Old Apr 23, 2012, 12:01 AM
dmcquinn is offline
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2-part epoxy is good for gluing things to styrofoam.
Old Apr 23, 2012, 12:45 AM
lindart is offline
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Wiping/cleaning the parts with common rubbing alcohol helps. Epoxy generates heat while curing, so use it in as small amounts as possible.
Old Apr 23, 2012, 11:03 AM
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Or let it sit in it's mixing container until some of the heat bleeds off, but before it half cures. Then apply.

For your case you could use a bit of low temp hot glue behind the mount then use some epoxy around the edges. But it really depends on motor size.
Last edited by dedStik; Apr 23, 2012 at 11:09 AM.
Old Apr 23, 2012, 12:22 PM
BMatthews is offline
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Quote:
Originally Posted by dedStik View Post
Or let it sit in it's mixing container until some of the heat bleeds off, but before it half cures. Then apply.

For your case you could use a bit of low temp hot glue behind the mount then use some epoxy around the edges. But it really depends on motor size.
A few things;

First you guys are WAY over estimating the amount of heat epoxy produces. In thin films such as used in a repair of this sort it you won't even feel the warmth on the repair. The heat only becomes an issue when it's kept in a bigger volume such as an ouce or two left standing in the mixing cup. THEN it can become very warm as it cures. The way to combat this for bigger mixed batches is to mix it thoroughly in a cup then immediately pour it out onto a wider container and apply it from there. But for small batches mixed up from a couple of "worms" of epoxy squeezed from the tubes or bottles onto a notepad page or other sheet and mixed with a spare stick of something and applied you'll never notice any warmth.

Second by the time it begins to stop giving off heat it's getting too gelled and thick to use correctly. Mix it, spread it and stick the parts together as soon as it's well mixed and applied. By using it while it's still the most liquid you'll get a much better bond to the surfaces of the repair parts.

If it needs to be thickened a little to fill some gaps then mix in wood sawdust or some form of light filler such as phenolic or glass microballoons. Again do not wait for it to thicken from curing or you'll simply hurt the bond strength.

Glue spread around the edges of a joint does very little other than add weight. So I don't recomend the idea of hot glue then smearing epoxy around the edge. If you want to do such a thing then the right way to do it is to use some fiberglass tape along with the epoxy to create a strong skin around the edges that extends over the joint. A repair of that sort will connect the motor mount back onto more of the foam. But simply smearing glue over the joint is a waste of time. And hot glue simply does not stick to metal all that well.

To do this repair with epoxy you want to ensure that the mount will fit back onto the fuselage very accurately. If it's a clean break it'll sit in place with little or no slop. If there is any slop then you'll want to devise some way of shimming or pinning the mount with something or building up the foam with scrap and reshape the nose in preparation for re-attaching the mount so you know it will sit back in place at the right spot and at the right angles of down and side thrust. For such things 1/4 inch of fore or aft displacement will matter and as little as a half to one degree for the down and side thrust angles of the mount will show up in how the model flies.


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