Epoxy or finishing resin?

[Glenn (Gravitywell) Reach]

This may sound like a pretty dumb question, but what's the difference between Epoxy and Finishing Resin?  Other than one being thinner than the other, I really don't see or smell a difference.

[Tim Wescott]

If you mean what's the difference between epoxy glue and epoxy finishing resin, then not much, at least not chemically.  They add stuff to the glue to thicken it, they don't add it to the finishing resin.

There is (or used to be) polyester finishing resin, but you can smell that difference quite distinctly.

[Brett Buck]

This may sound like a pretty dumb question, but what's the difference between Epoxy and Finishing Resin?  Other than one being thinner than the other, I really don't see or smell a difference.

   You mean "polyester" finishing resin VS epoxy, or *epoxy* finishing resin VS regular epoxy adhesive? I guarantee you can tell the difference between polyester finishing resin and epoxy, polyester has an absolutely unmistakable and very strong smell, and epoxy is much different and much less smell. If you have ever smelled Bondo, that's what it smells like, because Bondo is polyester base. It's also the resin used to make fiberglass boats, car bodies, etc.

   Polyester finishing resin is long obsolete, the nitwit aside. Some people still use it, particularly when they in a hurry (because you can speed up the cure by using more catalyst, to the point its *way too fast*), but it is also extremely brittle. I would also caution you that the catalyst for polyester resin (methyl ethyl ketone peroxide) is one of the most dangerous chemicals you will come in contact with in normal life, and in particular, it will blind you *instantly and permanently* if it gets in your eye.

    Epoxy finishing resin VS epoxy adhesive is primarily about the viscosity and amount of filler. Most consumer adhesive epoxy "hardeners" are chock full of non-reactive fillers (sometimes, *castor oil*) to get the mixt by volume up to 1:1 or 2:1 from the normal about 4:1 or 8:1 or less, depending on the type. This also makes them more flexible and in some senses, tougher. Finishing epoxies tend to have much lower viscosity than adhesives, making them easier to brush, and much less filler, so it set up harder and is easier to sand, instead of getting all gummy.

     Aerospace epoxies generally have no fillers, and are mixed at the factory for quality control purposes, then frozen before they cure. To use them, you warm them up and then apply them.

   Epoxy and even polyester are useful because they are much more stable in a shorter period of time than air-drying materials like dope. They shrink *a little bit* but even the really slow ones are stable enough in a day or two. They use Bondo on cars because you can mix it, apply it, wait an hour, then sand it down and paint over it later that day. Epoxy usually takes longer but is a lot more suitable for our purposes, since our substrate is flexible wood rather than steel.

     Brett

[Glenn (Gravitywell) Reach]

Thanks for the quick replies fellas.  I did mean EPOXY finishing resin!  I would never use the other....far too toxic!

[Brett Buck]

Thanks for the quick replies fellas.  I did mean EPOXY finishing resin!  I would never use the other....far too toxic!

   And don't overlook the cost of a divorce, because polyester smell might be considered "alienation of affection" or "spousal abuse".

     Brett

[Brett Buck]

Thanks for the quick replies fellas.  I did mean EPOXY finishing resin!  I would never use the other....far too toxic!

    Epoxy (particularly the hardener) is moderately toxic, too, but not acutely so. The industrial types that are not pre-mixed scare me a bit, and I am more-or-less certain that exposure to them when making carbon fuel tanks contributed or caused Jim Tichy's unfortunate demise. I know he took nearly no precautions to avoid exposure, and a lot of his symptoms where classic chemical exposure affects.

     I am not a worry-wart, in particular, but I wear clear plastic chemical exposure gloves when working with significant amounts of industrial epoxies like Epon, etc, or finishing epoxy hardener (which also has an unfortunate tendency to destroy the polyethylene or polypropylene bottles it comes in). Just have to be sensible about getting it on you, small amounts won't matter, just avoid getting large amounts covering your hands, etc.

   You should also be aware that adding more "hardener"/Part B to most consumer epoxy will not make it cure faster or better, it will likely just leave more unreacted filler in the matrix and make it gummy or sticky. It works with unfilled epoxy, but it also does unknown and unpredictable things to the characteristics of the cured resin - usually, the faster it cures, the more brittle. Mix it as directed (usually 1:1 or 2:1 by volume, with the relative weights occasionally given). Also, *mixing it thoroughly* is critically important, the longer the better, you can't overdo it as long as you get it on the surface/joint before it starts to cure.

     Brett

[George Truett]

They call all of their Epoxy Z-Poxy (5, 15, 30 and finishing).  If you're asking about the finishing resin, according to the packaging 20-30 minute working time and 3 hour cure.

[goozgog]

Hey Motorman,

  I find the shelf life of most epoxies is between
one and two years before it starts to crystallize.
The hardener seems stable over six years.

  What everyone needs to know is that warming
crystallized epoxy RESIN melts it back to usable
liquid. Don't warm the hardener !

  I melt it in a cut off soda can using my hot air gun.
Go slow, warm it until it melts and goes clear,
like ice does.  It only takes a little heat.

 I have never seen any differences when using
warmed epoxy resin on model aircraft.

Cheers! - K

[Glenn (Gravitywell) Reach]

What an excellent tip Goozgog!  I knew that heat will release an epoxy glue joint, but never knew it will reconstitute old stuff.  I will have to use that.  I have resin that is totally yellowed with age and is crystalized.  I just don't use enough of it I guess!

Brett.....that comment about, "...overlooking the cost of a divorce, because polyester smell might be considered "alienation of affection" or "spousal abuse"."  That made me laugh out loud!  Made my wife ask what was so funny so I told her.....for some reason she didn't laugh.  Oh well.

[Tim Wescott]

   And don't overlook the cost of a divorce, because polyester smell might be considered "alienation of affection" or "spousal abuse".

     Brett

The folks that complained the worst about the polyester smell at my dad's factory were the dope smokers.  There's just something about smokin' dope that makes the smell worse.

Not that I'm, like, trying to insinuate anything.  Oh no.

[frank williams]

Glenn
The Zap Zpoxy Finishing resin is great stuff.  Its the new go to finishing method.  The beauty is that it sets crisp and hard no matter how thin you put it on.  Squegee it across the wood.  Squegee it again so there is nothing left.  Wipe it with paper towell so ther is really nothing left on the wood.  Come back in the morning and hit it with a piece of 320 paper and it just powers off.  It hardens the balsa so that your next dope and filler coats will not soak in at all.

[Will Hinton]

You're spot on, Frank, and I use it the exact same way on my custom guitar finishes.  It seals the grain without adding stiffness or weight and I can spray a minimum number of coats of finish so as to not suppress the resonance of the instrument.  I LOVE the stuff.

[Dennis Saydak]

You're spot on, Frank, and I use it the exact same way on my custom guitar finishes.  It seals the grain without adding stiffness or weight and I can spray a minimum number of coats of finish so as to not suppress the resonance of the instrument.  I LOVE the stuff.

Ditto for me, 

[Will Hinton]

Lookin' good Dennis, lookin' good.  A H^^lways a good place to get one to, sort of like finishing the cowling on a stunter.