Gelcoat Repairs; Storage of Unused Product

I have some upcoming repairs to perform around my Impex Assateague’s skeg box, as you’ve probably seen in some of my previous posts. I now have the supplies to do the job, so to put it off any further would constitute procrastination. I have a pretty good plan in mind to effect the repair, but despite being handy and technically competent I have little experience with fiberglass and gelcoat.

The I’d like to make up a few larger batches to colour match three different colours on my boat, plus a smaller repair on another. I’d like to then catalyze a small amount for the repairs while keeping the same colour for future repairs, or to make small adjustments to if the colour is not acceptable.

questions at the top of my mind right now are regarding the storage of gelcoat with added pigments but no added catalyst. Do I need a perfectly air tight seal? Are there particular container materials that the gelcoat will chemically react with, and thus to be avoided? Is this even a worthwhile thing to do? What’s the shelf life of gel coat in general?

I don’t know about specific types of containers, as I’ve only stored mine in the original can. And I’ve never stored after tinting, although that sounds like a really good idea if possible. But the can I have that I just used must be over 5 years old, and seemed to work as good as new just a few weeks ago. The catalyst is relatively cheap to buy, and in my experience, if it’s a year old, replace it. It’s no fun when the gel coat doesn’t set up, and not worth the risk of using bad catalyst.

Please share if you can confirm that storage after tinting doesn’t cause any issues.

@CapeFear said:
Please share if you can confirm that storage after tinting doesn’t cause any issues.

It’ll be a while before I know anything, but I’ll try to.

For storage, I’ve decided on short wide mouth canning jars. These are intended for jams, jellies, and such. The glass won’t have any problem with the gelcoat. I’m not sure about the seal material in the lid, but I’m going to give it a shot.

I’m assuming you are dealing with polyester gelcoat, since vynil ester has a very short shelf life. However, you might want to read the information on before you proceed with your project. I have used vynil ester gelcoat with excellent results and I was lucky enough to get the perfect match color from the boat manufacturer.

I think the information about the flexibility, adherence to the underlying layup, relative strength and water tightness as compared to polyester gelcoat might be of interest to you. Possibly a phone call to a gelcoat manufacturer would answer your questions about the shelf life of tint-mixed gelcoat.

In any case, if you have not previously worked with gelcoat, it is imperative that you find a very detailed instruction in exactly how to proceed. I could provide that, but it is a bit lengthy and you might already have taken that step.

You’re probably right about the superiority of vinylester, but it sure isn’t very popular among the sources I have to obtain supplies. If picking epoxy is difficult, picking gelcoat is virtually impossible! I ended up going with Evercoat Polyester Paste.|11344&product=42887585&code=023289006952

I’ll soon see what it’s like to work with, and time will tell how it holds up. After all, it’s a kayak - not a luxury yacht. I don’t expect it to last forever, and it doesn’t have to look perfect either. I’ll do my best work (which is usually better than average) but a few cosmetic blemishes aren’t going to detract from the functionality.

This little project is largely a learning experience. I’d love to have practiced on something easier, but it’s easier when there’s a “need” to do it, as there is now.

Current Designs says 90 day shelf life
Expand. I had some 1.5 years and it worked great. I kept it in the refrigerator. Make a test batch. Also watch catalyst amount and temperature you’re working in.

As long as your container is absolutely airtight, you can store it in a freezer and it will extend the shelf life dramatically. Use the smallest possible containers and split your large colored batch among them. That way, you don’t have to expose a large quantity to the air again when you do future repairs.

If you’re trying to match an existing color, make sure that you test it. Gelcoat often changes color as it cures, so a good match in liquid state is not necessary going to match once it’s cured. Frankly, the only colors that are easy to color match are white and black. Colors fade with use and even getting the original color from the manufacturer doesn’t guarantee a color match.

The paste-type gelcoat you have is excellent for the type of repairs that you’re doing, as it won’t run all over the place. Don’t waste your time trying to put Mylar over it to get a perfect finish as is often recommended, it’s not practical except on small and/or flat repairs. Just build it up a little proud of the surface, then sand it to shape. Blend and polish it with progressively finder wet/dry paper (up to 1500 grit), then using polishing compound to get the perfect sheen.

Thickening epoxy is really only necessary if you’re using it as a filler. If you don’t have any fumed silica, you could always use several small pieces of fiberglass to build up the area, shape it as necessary, then put larger patches over it. Be careful with the chopped strand mat; it generally has a binder that will only work with resins with styrene in them (polyester or vinylester), not with epoxy.

I have instructions for fiberglass and gelcoat repair on my website:

Thanks, @bnystrom . Great tips! Do you think I need to be concerned about adhesion to the epoxy? I have a small test piece that I laminated up when I first started. I’ll be using this to test out the gelcoat adhesion and flexibility before I apply it to the boat. That’s at least a few days off though, as I can only work on this in the evening.