Notes On Repairs To Composites (Fiberglass etc.) Kayaks

Regardless of whether your kayak is made of fiberglass, Kevlar, or carbon/graphite these are all composites, and the easiest way to repair them is with fiberglass (and resin).

KA does not sell repair fiberglass repair materials. Tap Plastics or Fiberlay are good sources locally and West Marine has some too.

The following are tips for buying the materials you need to do the job and for choices you need to make when repairing your kayak.


Fiberglass Repair Kits are not generally the way to go for at home permanent repairs. They are usually too small and sometimes have the wrong type of resin and/or catalyst. So make your own "kit" using the following guidelines.

For resin, be sure to use Vinylester (not the more common Polyester). Vinylester will bond to either one, but Polyester will only bond to Polyester. Your kayak is made with Vinylester like special epoxy (think of it as Vinylester).

For small repairs, you can also use epoxy, but don’t breath while doing it. And from then on you’ll need to use epoxy to bond to that repair.

And each type of resin can be formulated as either “Laminating” or “Finish” resin. Finish sometimes says “wax added” (which I think means it has styrene added, more on this below).

With Finishing resin, it will cure non-tacky with no bag covering it (open to the air). This is great unless you are going to have to add another layer in which case you’ll have to sand and prep (wipe with acetone) between layers.

With Laminating resin, if you are planning to add another layer then let it cure with no bag over it. It will harden but stay tacky and as long as no dust contaminates it you can add another layer without sanding or prepping the surface. Or if you are not planning to add another layer after it cures, then you can cover it to keep air out and then it will cure non-tacky. If later a second layer becomes necessary then sand and prep between layers.

You can convert Laminating resin to Finish resin by adding a small amount of styrene to the batch before adding the catalyst.

For small patches with Laminating resin I use wax paper to cover the repair to make it dry non-tacky. For large patches or where there are compound curves then I use stretchy plastic film (I forget what type of plastic it is but ask the store what to use)

There are at least a couple types of Catalyst. The best is MEKP. You only need an oz. or so of cat.

All the same applies to Gelcoat except you don’t get a choice of Polyester/Vinyester/Epoxy with Gelcoat. Gelcoat is just Gelcoat except it can be Laminating or Finish.

If the damage makes a leak, use a layer of fiberglass “matt” to seal it. Matt is sold by the yard or sometimes in a repair kit. If the damage makes it weak, use fiberglass cloth to reinforce it. You can buy fiberglass cloth by the yard like fabrics, but for small repairs I like using fiberglass seam tape (you can get it in 1”, 2” or 4” rolls). Seam tape has finished edges so it is less messy than if you cut a small square out of a fiberglass cloth.

For small repairs, I like to wet out (saturate with resin mixed with catalyst) my fiberglass (matt and/or cloth/seam tape) on a piece of cardboard and then lift the whole “pre-pregnated” patch up off the cardboard and apply it to the boat then squeegee it into place to get the bubbles and excess resin out. But the standard way is to lay the glass on the boat and then pour the resin with catalyst over it and squeegee it.

For mixing small (1oz) batches of Gelcoat I like using plastic cups made for medicine sold at drug stores. They are about half the size of a shot glass.

Round toothpicks and tongue depressors are good for stirring and dripping gelcoat into the repair.

Always use clean new sandpaper to prep the area. Usually 150 – 250 grit.

Unless you have a well ventilated shop with positive air flow and a vent-hood plus a great chemical respirator mask, do all your mixing, patching, and curing outdoors on a calm, sunny, 70F, dry day. And wear a mask if doing a lot of this, otherwise hold your breath.


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