[SOLVED] Best alcohol for thinning epoxy?

I use isopropyl 99% (1% water) rubbing alcohol that I buy at Safeway. It is a great epoxy thinner and I haven't noticed any loss of strength. I believe isopropyl doesn't attract moisture as much as the other alcohols. I have become a hero to my wife by painting a thin epoxy mixture on wooden kitchen utensil handles. It makes a tough waterproof plastic coating and she loves it. I have even used it to coat outdoor wooden and plastic parts to make them more weather resistant.

Marlowe

You are correct. The water in the over the counter "rubbing alcohol" will make the epoxy spongy. I used it ONCE. That was enough to go to the hardware store and buy denatured alcohol. BIG difference!

If you buy the 99% 'drug store variety' , it only has 1% water which is not enough to hurt anything. If you don't need a gallon , then $3 for a pint beats $8 per gallon in my book. Hmmm...how many gallons of epoxy could one thin with a gallon of alcohol ?

Ken Day

I don't know why you people keep recommending alcohol for thinning epoxy. I have always used laquer thinner. It evaporates fast, well before the epoxy starts to harden. Since there is less solvent left behind the coating is much harder. I have had a problem with a soft easily peeled off coat with alcohol especially if thinned greatly. With laquer thinner I can thin it about as much as I want.

Alcohol can be used with great results. The trick is, it must be used sparingly. Literally just a few drops or even less. Most people I suspect dump a capful or more in their mix and get the results mentioned. Experiment to see how little alcohol it takes to get the required results. I'm sure many will be surprised.

OK, go for it but don't say I didn't warn you when you end up with 'spongy' epoxy!

Alcohol evaporates faster than lacquer thinner. That's why I use it.

If you use the fast drying lacquer thinner, used mostly for primer coats, the opposite is true. In fact even with high gloss most of the product dries out before the alcohol. It's only the retarder that remains behind.

Thanks for the warning , but apparently you didn't read my post very carefully........the part where I said I've been using 99% for years with no problems.

Ken Day

Jim. Just found this info on the Bob Smith Industries web site.

Thinning Epoxy The one question that is answered most often by the technical experts at BSI is what can epoxy be thinned with. Isopropyl alcohol that is

90-99% pure is what works best. It is available from most drug stores at a reasonable price. Rubbing alcohol contains only 70% isopropyl with the other 30% being water, which can become trapped in the cured epoxy. Denatured alcohol (which is ethanol with an additive to make it undrinkable) has also been used to thin epoxy. Acetone will thin epoxy but will sometimes change the curing characteristics. Also, epoxy thinned with acetone can have an adverse effect on white foam. Epoxies can be colored with the various tinting compounds designed for acrylic and latex paints, which are available at many hardware stores. Colored FINISH-CURE, thinned with isopropyl alcohol, has actually been applied with a spray gun to form a beautiful final finish on several models. Of course, the immediate clean up of the spray equipment is extremely important.

Ken Day

I understand. the 99% is probably great! The rubbing alcohol has more water in it I guess. The rubbing alcohol is what is typically sold in the drug stores.

Many thanks to all for their responses to my initial question.

In separate batches I tried using straight industrial methanol and the 91% isopropyl. Both worked well enough for my needs.

I did come across one interesting effect. It would seem that WHEN the alcohol is added is important as well. I added about 8-10 drops of alcohol to both batches of 30 minute epoxy ( 15 ml total epoxy in each batch). This mix wetted out the cloth well enough. As I was finishing the spreading of the epoxy on the center section I noticed the epoxy in the cup had thicked very slightly, so I added 2 more drops of alcohol to thin it out in case I need it. As things worked out I didn't need it.

The surprise came about 12 hours later. The twice thinned epoxy in the cup set up VERY spongy and rubbery- if you rolled the cured epoxy between your fingers it just crumbled into bits.

I was in near panic as I checked the epoxy on the wings. To my relief the epoxy on the wings had set up well- not quite as hard as a true finishing resin would have been, but it was hard and the edges of the cloth sanded out as you would have expected.

Moral of the story- it seems the alcohol can only be added at the initial mixing of the A and B parts of the epoxy. If any curing has taken place adding even 1 or 2 drops more alcohol will destroy the mix.

Thanks again,

Mark D. Fain

On Tue, 12 Jul 2005 22:24:34 -0400, "Mark D. Fain" wrote in :

Thanks for telling us the rest of the story.

Your discovery about WHEN to add the thinner is very illuminating!

One good method for thinning epoxy without using lacquer thinner or alcohol is with a heat gun. Dab some on, blow it with hot air, and tilt the surface to make it run. Or use a small brush to move it around when it's warm. Works great.

Sport Pilot wrote: