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What would you use to thin out epoxy, and does it weaken the bond?

britbrat

Isopropyl alcohol -- no it doesn't weaken the bond.

bbmass

My Feedback: (2)

I prefer denatured alcohol. I use the rubbing stuff to clean up epoxy, but when thinning it to go over fibergalss I use denatured because you don't have to worry about water.

Sport_Pilot

Rubbing alcohol is about the worst thing you can use for thinner. It is about 30% water and much of the water stays in after it cures. This can cause the epoxy to be cloudy. This greatly weakens the bond. Don't use thinned epoxy for anything structural as some of the thinner will stay behind and weaken the epoxy. If you are using the epoxy for fuel proofing rubbing alcohol will work fine, but if you use a fast drying thinner such as laquer thinner or acetone, the finish will be harder and more scratch resistant.

J_R

Depends on what you're doing.

If this is the bond between, say, two pieces of wood, I would not thin the epoxy. The solvent could be trapped and the joint will have no integrity. Any solvent you use to reduce it has to evaporate before the epoxy sets. If, on the other hand you are fiberglassing or fuel-proofing a firewall, reducing it is fine.

Use a longer setting epoxy, give the reducer time to evaporate. PURE isopropyl alcohol, or denatured alcohol will work fine as a reducer. Do not use typical rubbing alcohol... it contains water and will be trapped.

You can also mildy heat the epoxy with a heat gun to make it thinner, however, this has the added affect of causing the epoxy to set faster. I do not perfer this method. If you get it too hot, you run the risk of fumes and fire. If you heat reduced epoxy, it will probably trap some solvent.

Sport_Pilot

Not entirely true. Here is a simple experement, Mix a couple of dab's of epoxy in an epoxy mixing cup, then fill it up with your favorite thinner and mix. It will take a while to cure but when it hardens you will find a soft white, almost foam like material. It will be very weak. The reason it is white is all of the liquid thinner trapped by the cured epoxy.

âûñøåå îäíî

ok, so i shouldnt use rubbing alcohol (isopropyl) as a thinner, and pick up some denture alcohol

i am using it to re-enforce my fire wall on an RTF .40 trainer with a .46 in it, i want to stregthen the wood its self, and the joint (i used CA on the joint, and then saw that Epoxy was better) because of a crash

J_R

Sorry, that was meant to imply that if it did not evaporate, you have a problem.

J_R

Personally, I would put triangular stock at the joint and use aliphatic resin (titebond or similar). With just a few exceptions, like glassing and fuel-proofing, I hate epoxy because of it's weight.

If you are bound and determined to use epoxy, add some glass to strengthen the joint. Epoxy relies on a surface bond, and has very little tensile strength. Pour some on paper, let it set and bend it... it snaps with very little effort.

Sport_Pilot

Since not all of it ever evaporates you will have a problem, just to a much lesser extent. If it dries well enough that the thinner is not making molecular contact with itself it will dry clear and strength loss will be minimal.

Sport_Pilot

I would use the triangle stock as JR mentioned. If weight was not a large concern, and often it is not near the engine, then I would also lay 2 ounce fiber glass and one coat of unthinned epoxy.

britbrat

Rubbing alcohol is not Isopropyl alcohol -- Isopropyl is OK.

JetflyerJ

My Feedback: (67)

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JetflyerJ

My Feedback: (67)

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the bottle says
"Isopropyl
Rubbing Alcohol
70% by volume"

britbrat

Ooops -- pure isopropyl is OK.

Schpankme

As to your Epoxy Thinning question (strength):

There are two methods of temporarily thinning epoxy. One is to heat the mixture and the other is to add solvent to the mix. The goal of both methods is to reduce the epoxy’s viscosity.

Adding solvent is a simple method of thinning epoxy, but unlike heat, the strength and moisture resistance of the cured epoxy are drastically affected. There are a large number of chemicals available to thin epoxy - acetone, lacquer thinner and denatured alcohol are the most commonly available and do a good job of reducing viscosity. For a variety of reasons, "fast evaporating" lacquer thinner is more appropriate for thinning purposes than acetone or alcohol.

Adding 5% lacquer thinner to epoxy:

reduces viscosity by 60%
reduces compressive strength by 35%

Adding solvent extends the pot life and cure time and jeopardizes the reliability and predictability of cure.
Adding volatile solvent may cause shrinkage of the cured epoxy.
Adding solvents alters the color of the cured epoxy.

Solvent thinned epoxy cannot be used as structural adhesive.
The solvent used to thin epoxy may damage the substrate.
The addition of more than 5% solvent results in an excessively flexible cured material.
Solvents may be hazardous to your health and proper ventilation is mandatory.


Utilizing a Hot Box (small insulated box with light bulb) to pre-Heat the resin/ hardener components of epoxy, substantially lowers its viscosity. Large batches of pre-warmed epoxy cures much more quickly than you may be accustomed to, excessive heat (more than 120F) may cause the epoxy to harden too fast, especially in thick applications.

__________
Schpankme

"Far Out" - John Denver

JimTrainor

methyl hydrate (a.k.a methanol) from the paint department at the local hardware store will do it

pt19 flyer

My Feedback: (1)

hi

you do not want to use the 70% stuff, use either 95% isopropyl <from drug store or walmart> or go to liquor store and buy 190 proof alcohol. I have used both with great success. here the less water content the better.

happy flying

pt19 flyer