Epoxy problems
 

I race R/C sailboats in AMYA clubs. My Soling 1M developed a crack at the deck/hull joint. I sanded the crack and put fiberglass and worked epoxy into the material. After three days, the epoxy has not dried and remains sticky. The epoxy was about one year old.

Since it doesn't seem to be curing I think I need to take off the epoxy. What solvent will do this?

thanks for your comments....

Hi Ibrannnan ,

The solvent of choice for uncured epoxy is good ol fashioned rubbing alcohol . If it's been 3 days and still uncured , this should clean it off easily . In fact , when we fuelproof RC plane firewalls with epoxy , we use alcohol to thin it with , the alcohol evaporates and the epoxy cures just fine and we get a super thin layer that keeps the fuel from softening the wood .

PS , the alcohol usually comes in , what , 70% or 90% solution when bought at the local pharmacy ? , make sure to the the 90% stuff . Hope this helps ....

Id try a heat gun on it. Epoxy cures by heat. Dont get it too hot.

Thinning epoxy with other than the manufacturers suggested products leads to such problems as yours in many cases. While some get by with using alcohol, it is not recommended. To often this alcohol has a large percentage of water in it and this leads to problems. If you must use alcohol, be sure and get denatured alcohol at the paint store or hardware store as it is water free. That you get at the local drug store is often heavily diluted with water. By far the best solution is to just warm the epoxy when applying it as that lowers the viscosity and lets it flow out well and speeds up the cure. Epoxy does not dry, it cures; i.e. undergoes a chemical reaction which is easily impeded by contaminates such as water.

Thanks! I'll pick up some 90% alcohol today.

Good tip - thank you!

I've used 73% rubbing alcohol for both thinning & clean up W/O any issues.

Just rub in a thin coat of CA and the epoxy will cure.....

Larry

I buy the alcohol wipes at the drug store. These are the same thing they use on your arm before they give you a shot. They are 90% alky and are great for cleaning around glue joints and getting the stuff off of your fingers. They usually come in boxes of 100 for about 3 bucks.

My PERSONAL choice is Acetone. Have used it to clean up both epoxy and CA, with no after effects.

90% alcohol buddy. 100-90=10% water. You call that high water content

I'm with you on this.

Denatured contains water. With rubbing alcohol, you get water and a little oil. Neither are good in epoxy.

Denatured alcohol does not contain water. It is ethanol with a little methanol so you will not drink it!

Lots of misconceptions about epoxy here. The solvent of choice for clean up and clean prior to bonding is acetone. CA WILL NOT make epoxy cure. Heat helps and we either heat cure or post cure just about everything we do at work ( I"m a composites technician by trade ). After 3 days unless it has been sitting in 50 degree temp all that time heat will not help. With additional heat it may cure up enough to not be sticky but it won't have the strength required. My suggestion would be to clean all the previously applied epoxy with acetone and start all over. The OP did not mention exactly what epoxy he was using but should be using a quality laminating resin. Most readily available would be West Systems or Z Poxy. Most 1:1 ratio hobby epoxies are pretty much junk and are a poor choice for this type of work. After cleaning well, mix up some laminating resin, it is important to get the mix ratio exact. Mix in some milled fiber until you have consistency of tooth paste and then force into your crack then cover with Mylar packing tape. The tape will keep the resin mixture from running out the other side of the hull if the crack goes all the way through. Put next to a heat source that will maintain 70 to 90 degrees temp on the area. A shop light with 100 watt bulb works well for this. After a few hours you will be good to go.

For the discussion of alcohol usage with composites Isopropyl alcohol is what should be used, it can also be referred to as isopropanol. Not what I prefer to use as all alcohols once opened will start to attract moisture.

:p:rolleyes::eek::confused: All of the above but the purer the alcohol the better the fix. Acetone could damage other finishes like paint in the process. Are'nt you glad you asked? :rolleyes:

I though denatured alcohol was called denatured because it was modified to be non-drinkable and thus able to be sold without all the alcohol taxes

There are a lot of things that will remove epoxy - any drug store or solvent alcohol, lacquer thinner, acetone, MEK, Xylene (Xylol) all work. I've also heard that plain old vinegar works but I've never tried it.

My concern would be not damaging the glass hull with a solvent that attacks it. So first I'd try alcohol and then if that wasn't getting the job done (it should though) I would try lacquer thinner. I would stay away from acetone and MEK even though lacquer thinner has acetone in it sometimes.

When it's clean just degrease the crack really well with TSP or something (not dish soap). Let it dry thoroughly and go at it again.

I hope the OP will clarify this but just about every sailboat hull I have ever seen has been painted in the mold. If its an epoxy lay up the the finish is also epoxy based, if its polyester then it will be gel coat. Either way the acetone will not hurt either. The OP could even add a pigment to the epoxy to better hide the repair.

The reason your expoxy did not cure is because for some reason it did not get mixed properly, not enough hardner unless you have bad expoxy but I have expoxy that is over a year old and it has never given me any problems. The correct way to fix this is really to sand off the uncured epoxy and then redo it.

Did a little searching around and the hull in question could actually be made from styrene plastic. If that is the case then obviously do not use acetone. If it is a styrene hull then there would be better alternatives to epoxy for the repair such as Shoo Goo or Goop .If used correctly acetone could actually be used to fuse the parts back together.

I use a considerable amount of epoxy in model airplanes. Been so since I remember the first ones on he market. Then the 5 minute came out and some of us thought we had died and gone to H---en. ;)
Regular Alcohol has always been the choice for clean-op. 70 - 90 whatever is in arm's reach. Sometimes when the shop is cool, and so is the epoxy, I hit it with the heat gun. It gets runny, then cures in a rush. That works well for me especially when I want all possible cracks and crevices fuel proofed.

Do you see what I mean buddy?

Bob

One of the problems that causes epoxy to not cure is mixing different epoxies; such as part A having a 45 minute cure time and part B having a 5 minute cure time, or vise-versa. Another, is the fiberglass has oil residue, or still having certain types of paint on it that was not completely sanded off the repair area.

I've used acetone with great success (plus a lot of rubbing with colths) to remove uncured epoxy.



I'd cut out the section that did not allow the epoxy to cure, then re-glass.