Amateur gel-coater, not

Man, do I suck at this. Coming from a wooden trawler which I Awlgripped myself to a fiberglass boat with an Awlcraft painted hull and a gelcoated topside, I figured that someday I'd want to learn the art of gelcoating. As an introduction to this art, I attempted to gelcoat and small polyester resin coated box I made to cover the fist-sized air compressor for my new air horn (replacing the anemic sounding electric OEM). I used a two-year old can of UNOPENED waxed gelcoat and mixed in the exact amount of catalyst for 1.5% mix (73-degree F, about the temperature yesterday), and, at the behest of a friend, I spryed on PVA to help the hardening process. Today I found the whole box covered in a sticky mess and just rubbed it all off with acetone for a fresh start.

I called the company I bought the gelcoat from, and they said the shelf life of their product is six months. But it was never opened. Anybody buy that excuse?

A true expert is coming by in a couple of weeks to experiment on touching up some Hurricane Michael scars on the hull, and I intend to turn this box and the gelcoat (which he thinks should have been ok on the shelf unopened for two years) over to him. He mentioned some other chemical which he would use to enhance the process, but I cannot remember it. He did a superb job making a couple of vanity sinks out of fiberglass/gelcoat on the trawler; so I am just gonna wash my hands of this one. At least I got the box made and fiberglassed with polyester and ready for the gelcoat.

Ya know, sometimes you just have to hire out! ��*

Yes, resins do have a shelf life. So do caulk and some paints.

I guess you are both right. Time to let the expert mess with the "expired" GC.

This guy can teach you about fiberglass repairs. And yes, he even says that gel coat has a shelf life. http://www.youtube.com/channel/UC0kDqq-pSzdqFUk3oTaHBuA

You can probably make it work, but I spend too much time and effort getting ready to do glass work not to use good and current supplies. And I agree that Boatworks Today has some great how to videos.

Did you leave it in the open air? Someone I know once told me to put plastic wrap like on it so that it couldn’t breathe while curing. I don’t know where I remember that from though. But it made me cover a little thing I was doing with a plastic soufflé cup taped over the repair (filling small hole) because of this old tale I remembered...... at 60, I do other silly things as well ....

everything seems to have a shelf life. Even the kids seats in the back seat of my car.
I have done a little gelcoating. I patched the holes left by screws when I removed some snap fasteners around my windows one year, the holes left when I removed a pair of undersized life rings another year, chips and gouges fixed several other years.

The gelcoat I use has been opened several times over the last 15 years, but was re-closed with a hammer after every use, so very little new air has been introduced into the pint can. I used so little of it that I still have enough at that rate for another 20 years. The last time I used it, it was as good as the first time, so no, I don't think its shelf life is a problem.

I have tried the saran wrap trick to get a shiny surface. I ws never able to get it perfectly flat and smooth in filling holes, so I generally don't. Instead I use a good cutting compound for a shine and it turns out much better.

He said he used PVA on it to exclude air so it would cure. PVA is one way to cover the gel coat, saran wrap or something similar is another way to cover it. If not covered to exclude air, the gel coat will not go off and harden.

More likely the catalyst was old. MKEP will get weak and will not set up. I found out the hard way. It’s cheap so best to always use new. Once you get a few successful batches under your belt you will find out its EZ. I prefer now to epoxy.

Hardener has a shelf life as well. If you're using waxed gelcoat, the wax surfaces and provides the air barrier to allow it to harden. Mixing is key. An experienced guy who worked with me on rebuilding my muffler taught me to use a balance scale to mix in precise proportions. It was enlightening. Mixed a small test batch, then adjusted the ratio. The objective was to insure the mix kicked right and would cure out in the correct amount of time. Although we were working with epoxy, the same applies to polyester resin. Allows you to control the mix for consistent results from batch to batch. That's key, particularly for a novice.

The gelcoat is usually not the problem but the MEK needs to be a current bottle. Do not use inexpensive or hardware store hardener. I have used many products from www.FGCI.com in St. Petersburg, FL. They gave me a mixing chart for 1.25%-3.00%.
When in doubt, pour an ounce of gelcoat in a mixing cup (do not use a wax lined paper cup), and then count in 10 drops of MEK. Mix for a slow 60 seconds, being careful to mix the sides in to the middle.
Do your gelcoat in a well ventilated space and wear gloves.

I’ve done a lot of gel coating over the years, and the big lesson I’ve learned is to not use it unless it’s absolutely necessary to do so.
2 part PU paints are so much easier to use, more waterproof, last longer, more scratch resistant, and when you’re done with the application, you’re done, not just ready to sand three more times and buff out, then wax.

Bite the bullet , paint the boat , old gel just keeps getting older and worse looking.

HenryD said:

The gelcoat is usually not the problem but the MEK needs to be a current bottle. Do not use inexpensive or hardware store hardener. I have used many products from www.FGCI.com in St. Petersburg, FL. They gave me a mixing chart for 1.25%-3.00%.
When in doubt, pour an ounce of gelcoat in a mixing cup (do not use a wax lined paper cup), and then count in 10 drops of MEK. Mix for a slow 60 seconds, being careful to mix the sides in to the middle.
Do your gelcoat in a well ventilated space and wear gloves.

Click to expand...

Agreed on FGCI, they have a lot of knowledge and stuff there. However, they won't mix less than a gallon of gel coat. I use Fiber Glast (I believe in Atlanta) for smaller quantities of gel coat.

Right about the MEK (and it's not off the shelf MEK, it's MEKP... quite expensive, but you don't need much). If not used, it won't dry.

kapnd said:

I’ve done a lot of gel coating over the years, and the big lesson I’ve learned is to not use it unless it’s absolutely necessary to do so.
2 part PU paints are so much easier to use, more waterproof, last longer, more scratch resistant, and when you’re done with the application, you’re done, not just ready to sand three more times and buff out, then wax.

Click to expand...

Agreed that PU paints are a better product, but would argue they are not easier to use. They are often very thin and have to be sprayed carefully. Applying by hand it really hard and requires really high quality brushes and skill. Also, almost impossible to do a repair and blend in. Have any suggestions on that?

at least you got the fiberglass right . i have just sanded off my first attempt .

Waxed gel should need to be covered or need PVA...that may have been the issue.


While paint has its pros and cons...no need to paint a boat with good gel that just needs repairs.

I've used expired gelcoat many times. Never had an issue with it.
Also never covered it with anything, just pretty much brushed it on.
I keep it in a "cool can" so I can get several coats with one mixed batch.
I've also used old MEKP, Home Depot MEKP, never had an issue with either.

I’d say the OPs failure was most likely the MEKP.
It is especially susceptible to UV degradation, so keep it in the dark, not on the windowsill. I throw away what I don’t use, buy fresh for each project.
Old gelcoat seems to work ok for me, I’ve even revived it with some laminating resin, but wouldn’t recommend that for critical finish work!

I had a quart of Spectrum Color gel coat that I needed to repair some cosmetic storm damage in 2006. I've been using that can to make ding repairs ever since. With age and constant exposure to air, the gel coat has the "consistency" of frozen ice cream. It's is stored in an air-tight container down in a cool cellar. It will form a hard crust on top over time. When needed, I punch through the crust, take a dab of it, work in some MEK to a paintable consistency, then use the normal 2% MEKP catalyst. On any flat surface, I'll cover the area of repair with a taped-down piece of acetate sheet. The PVA is OK to cover small horizontal areas. The acetate sheet gives you a finished feathered, smooth, and flat surface. I wouldn't use old gel coat for any extensive repair. Either new gel coat or 2-part polyurethane, sprayed or roll-and-tipped. For spot repairs, gel coat is softer than 2 part PU, making wet sanding and buffing easier.

This may not work with gel coat material, I seal my paint cans with propane, I ‘squirt” unlit of course propane into the can to drive out all the air and carefully put the cover back on. Unfortunately there is enough moisture in latex paint that if you leave it too long the interior of the can will rust.

The two components were kept in the unopened shipping cardboard box until the day before it was used.