How To: Six reasons for using epoxy in fibreglass boat repairs
Not sure whether epoxy has what it takes to fix your fibreglass boat? “It’s versatile, strong, reliable – and more than a match for polyester resin”, says Hamish Cook, Technical Advisor at West System International.
Fibreglass boats – like all boats – get damaged. It’s inevitable. Collisions and groundings cause everything from small nicks to serious structural damage. And longer-term problems like water osmosis, delamination and blistering can leave you frustrated and off the water too.
For many years, the automatic response to many issues was to reach for polyester resin. But as hulls have become thinner, lighter and more flexible, they’ve become harder to repair – especially with polyester resin. Step forward epoxy…
Epoxy is a great adhesive
One reason that an epoxy product such as WEST SYSTEM® Epoxy is so useful for fibreglass boat repairs is that it’s an incredibly effective adhesive. It creates a resilient bond to fibreglass, cured polyester laminates, wood and metals – even when you only use a thin film. Polyester resin struggles in comparison.
Epoxy is ideal for wetting out fibreglass
If you’ve ever tried to spread cold butter on a piece of toast, you’ll know roughly what it’s like to wet out fibreglass using polyester resin. You need to work hard to get an even, consistent coating – normally using a foam roller, brush or metal paddle roller. With epoxy, it’s like using warm butter – the epoxy does the work for you. Brush the surface you want to wet out, leave it, and the resin will get to the right places and wick right into the fibres. Which means less time working, and more time eating toast.
Epoxy works well as a thin film
Polyester resin struggles to cure when it’s exposed to air. So when it’s used as a thin film it stays sticky and tacky, because a higher percentage of the resin you’re using is exposed. As a result, it has limited use if you want to repair well-cured fibreglass laminates using only a thin film. Epoxy doesn’t have the same problem. It works as an adhesive, coating and laminating resin even when used as a thin film – and it’s less likely to develop micro-cracks too.
Epoxy works at a range of temperatures
Polyester resin manufacturers typically recommend that you use their products in temperatures of 15°C or higher, which can be a problem if your workshop drops below that. Use the right hardener in your epoxy mix, however – for instance WEST SYSTEM 205 Fast Hardener® – and you can work on repairs at temperatures as low as 5°C by following our guidelines for using epoxy in cold conditions. Epoxy works well in hot conditions too – with the WEST SYSTEM 105 Epoxy Resin® and 209 Extra Slow Hardener® specifically designed for extremely warm and humid conditions.
You can control how quickly epoxy cures
By using different hardeners – such as WEST SYSTEM 205, 206, 207 or 209 Hardeners– you can tailor how quickly epoxy cures, giving you more control over your repair. And while you can add a catalyst like MEKP (methyl ethyl keytone peroxide) to polyester resin to tailor curing times in cold temperatures, using a catalyst creates a less effective bond.
Epoxy shrinks less than polyester
Polyester shrinks as it cures because the styrene molecules evaporate. That’s less of a problem on small fixes, but if you’re repairing a big area it can cause a major headache. The shrinkage adds stress to the repair before you’ve even towed your boat back to the water, immediately putting extra pressure on the adhesive. Epoxy shrinks far less. So the bigger the repair, the more important it is to use epoxy.
Still unsure about which product is right for you? For expert advice on product selection, email our technical team at: techsupport@westsysteminternational.com.
