Building a kayak seat out of fibreglass is a repair solution for a broken plastic kayak seat or a means of cutting weight out of a kayak for those who want the lightest possible craft. Working with fibreglass is not something you need a great deal of experience with in order to do correctly. All you need to build a fibreglass kayak seat is a mould -- another kayak seat -- and the proper materials.
Spread release agent over your mould -- the kayak seat you are going to replicate. Cover the entire top of the mould. If you leave areas exposed, your fibreglass seat will tear or break when you try to pop it off the mould. Cut 2-by-2 foot sections out of your fibreglass cloth.
Mix the resin and hardener in the bowl. Stir them together. Lay the sections of cloth over your mould. It is not important if parts of the cloth hang over the edges of your mould, you will cut the extra off later. What is important is that you cover the entire top of the mould with cloth leaving no part of it exposed.
Dab the cloth with a resin soaked paintbrush. Do not wipe or spread the resin over the cloth or the fibres of the cloth will bunch and fray. Dab the cloth making certain to completely saturate it with resin. Allow the cloth to cure for two hours, then add a second layer. Allow the second layer to cure, then add a third and let it cure overnight.
Grab the edge of your cured fibreglass seat and pull it off the mould. Usually, it will make a popping noise when it comes off. Cut any extra off the sides that are not a reflection of the mould with your tin snips. Sand the top of your new seat gently. You just want to remove any rough edges or drip spots. Your seat is ready to paint if you choose to do so.