Preparing for a fibreglass boat repair


In this blog on fixing a crack or hole in your fibreglass boat, David Johnson explains why – before getting to work – you need to carefully assess the damage and plan exactly what’s required.

Abraham Lincoln once said that if you gave him six hours to cut down a tree, he’d spend the first four sharpening his axe. And that focus on getting the groundwork right before you get to work is useful for many tasks involving WEST SYSTEM® epoxy products – including fibreglass boat repairs.

Of course, if you’re faced with major structural damage or are simply not confident about what needs to be done to get your boat back to its best, you should seek the services of a surveyor or a professional boatyard.

But for many small fibreglass boat repairs you don’t need to be an expert. You just need to make sure you assess your boat and prepare carefully before starting work.

Assessing the damage to your fibreglass boat

It’s vital to look carefully at any damage to understand how bad it really is. Scrapes, dings and cracks are easy enough to spot but invariably there will be crazing through the polyester resin that extends beyond the point of impact – especially if the area has flexed over time since the damage was done. It’s not unusual for a ding the size of a dessert spoon to require a repair the size of a dinner plate. 

So begin by measuring the true extent of any damage. Shallow cracks that only affect the gelcoat layer can often be repaired by scraping out the crack then troweling in catalysed gelcoat.

Minor cracks that run through the gelcoat to the first chopped strand mat layers should be filled using a mix of WEST SYSTEM 105 Epoxy Resin®/205 Fast Hardener® thickened to the consistency of peanut butter using WEST SYSTEM 406 Colloidal Silica.

But deeper cracks that extend into the woven fabric require a structural repair. You can read more about the processes involved in part two of this blog: Ready to repair your fibreglass boat?  

Preparing to repair

The next stage before beginning your repair involves measuring the thickness of the damage. You need to use a pair of callipers for this – and then prepare the surfaces for adhesion.

If the damage has gone right through your glass fibre, you effectively need to create a circular scarf joint, tapering in to the point of impact. So begin by removing all damaged material using a grinder to cut down to solid laminate or a saw to enlarge a hole to solid undamaged laminate. It’s a good idea to tap the surrounding area using a metal object (a coin is ideal) afterwards to check you’ve done this properly: any remaining voids or fractures will sound dull when hit.

You then need to grind a bevel around the edge of the repair with a minimum ratio of 12:1. So if your laminate is 6mm thick, the outer edge of the bevel should extend about 72mm (i.e. 12 x 6mm) from the inside edge of the hole. This creates an enhanced surface area for your bond, meaning you’re now in the perfect place to create a strong, reliable and long-lasting repair. 


Looking for the right epoxy products for your fibreglass boat repair? You can find all of the products mentioned above on our website.

For further information on anything mentioned in the article, contact our Technical Experts on the West System International support page.


Leave A Reply