Thinning Epoxy

[Dick Pacini]

I noticed today that my can of lacquer thinner says it can be used to thin epoxy.  Has anyone ever tried this?

[Steve Helmick]

Yes. It seemed to make Hobby Poxy II glue quite brittle. I've used alcohol since, and can't recall what sort of alcohol it is...but whatever they sell in the paint/hardware store for shellac thinner. I wonder if you can still get shellac?  Steve

[Paul Wescott]

Steve, shellac is still available through specialty woodworking stores and also online.  Last package I saw in person looked like a bag of very coarse brown sugar.  Hard to believe that something secreted by bugs can make furniture look so nice.

Paul

[Perry Rose]

You can use acetone also.

[Dallas Hanna]

Worth reading some of this on thinning epoxy.

http://www.westsystem.com/ss/thinning-west-system-epoxy/

HH

[SteveMoon]

I use thinned epoxy on every plane I build. I thin it about 50/50 with
denatured alcohol and brush it on the entire engine bay and tank
compartment for fuel proofing. Makes it much easier to brush on and
also allows it to run into any tiny gaps and cracks.

Steve

[Gerald Arana]

I prefer to use heat. Simply brush it on with an acid brush and heat with a monocoat heat gun. I remove all the excess......

Works great.

Jerry

[Lauri Malila]

Dallas,

Thanks for the West Systems link. It's quite good information but between the lines I can read the same thing as many epoxy suppliers and specialists somehow miss: they have allmost allways MUCH thicker laminates in mind and in that case the results of thinning epoxy are allways much more catastrophic. (And by the way, same applies to some post-curing instructions).
For gluing hardwood, heating the glue joint (50...70C) allways helps. The quicker setting the epoxy is, the bigger is the difference between a joint thats been cured in room temperature and a joint that has been cured in an elevated temperature. Years ago, as a part of my studies, I did very systematical lab tests with that. With normal 15-30 min. epoxy the shear strenght of glue joint (hard wood) can easily be doubled by curing it in higher temperature.
But about thinning; said simply, the problem has 2 aspects:
 -As mentioned also by West, you are altering the chemical balance of resin. Some specialists have also said that some components of the chemical cocktail can evaporate with the thinner and that naturally changes the end result.
But what we do is not rocket science and we glue mostly soft & porous materials. It's very easy to experiment which resin/thinner mix cures the hardest, i.e. which is easy to sand and then use that. With one epoxy it may be acetone, with another it's alcohol etc.
 -another thing is that you must be sure that the solvent has completely evaporated when the polymerization begins. That causes problems in vacuum bagging and with thicker laminates/closed molds but very rarely when you just lay a layer of thin glass cloth over wood. That's one good reason to use slower epoxies.

Lauri

[Randy Ryan]

Well, I'm not a chemist or an adhesive expert, but I've been thinning epoxy for years with lacquer thinner or dope thinner. Using the garden variety 30 minute epoxy sold under various hobby shop of dealer names, I mix per ratio, usually 1:1 and thin to suit. I do this for several reasons. Gluing large areas or even more for gluing skins on ribs or bulkheads it does 2 things for me, first is slows the kick time but second, it reduces the amount of epoxy used by a significant amount. I apply with acid bushes, squeegee, knife or popcicle sticks, whatever is the best for the application.

Flame suit is on, but in 35 years I have personally never experienced a problem and my models are a bit lighter.