Repairs and Maintenance [45]

by David winkworth

This Repairs & Maintenance article is specifically for glass fibre boats (and possible glass-sheathed wooden kayaks too).

I need to start with a word of warning:  If you have never mucked around with glass fibre/resin repairs, I strongly suggest that you get some experience with the system before tackling a repair on your kayak or setting off on a major expedition with a repair kit in your hatch. There is nothing difficult about it but doing the wrong thing could affect the integrity of your repair job.

So, getting experience? You could find a friend who has done glass fibre repairs and ask them to show you what to do… maybe get into their shed and do a few test patches on a piece of cardboard. You could buy one of the inexpensive Selleys glass fibre repair kits and have fun with that. Also, there are plenty of club members with experience with the stuff… so, use the ‘phone-a-friend’ option. Whatever you do, if you have a glass fibre boat, you should make it your business to know how to do minor repairs.

Nearly forgot… another word of warning… polyester, vinyl ester and epoxy resins are toxic and inflammable as is acetone, the solvent we use. Read the safety directions on the cans and avoid breathing the vapours by doing repairs in the open air or wearing the correct breathing mask. Wear glasses when pouring and handling catalyst. Wear old clothes and latex disposable gloves too (Andrew Eddy has a good supply of these… and probably shares in Ansell).

Glass Fibre Kayak Construction

Your kayak hull and deck is made up of the following: An exterior surface coat called gelcoat and a laminate behind that.

The gelcoat is a protective and waterproof layer for the laminate, and it is important that we maintain this layer in good condition by the occasional polish and repair of deep gouges through to the laminate. Gelcoat has no strength – all its strength comes from the quality and integrity of the laminate bonded to it. Gelcoat is also relatively brittle – extreme, repeated flexing and impacts of the gelcoat will cause ‘spider-web’ cracking and possible water intrusion into the laminate.

The laminate is usually made up of multiple bonded layers of resin-impregnated reinforcement material such as glass mat, cloth or rovings. ‘Higher-end’ boats may also have reinforcements of Kevlar, carbon or hybrids of both. The laminate may also contain ‘sandwich’ materials used to space reinforcement layers for greater flexural strength. The most common resin used is polyester. More expensive and higher performing vinyl ester and epoxy resins are also used. You should find out which resin your kayak is made from and use a similar resin in repairs for best results.

Know Your Enemy

Sun, sand, water and salt are the enemies of your kayak.

Just as your car has duco to protect the steel, your kayak has gelcoat to protect the laminate and naturally it is the gelcoat that will show the wear and tear first.

UV damage to the gelcoat will show up as a faded or dull surface. In more extreme cases it may be chalky – some of the gelcoat colour will come off with a finger wipe. You can easily restore gelcoat lustre with polish. I use an ordinary silicone car polish such as Kitten Cream Polish. It’s cheap at Coles or Woolies and works well. All the guff you read about special fibreglass polishes is just an attempt by the manufacturers to get you to buy 5 cans of their product instead of one or two! Silicone polishes (most available polishes are silicone) will give a deeper lustre than carnauba waxes.

A word on silicone polishes: they don’t mix with glass fibre molds and gelcoat spraying. Keep them away from your moulds at all times.

If you have light scratches to remove, the cream polish is unlikely to do much. You need an Extra Cut polish. It’s available in the same cheap brands and it will move more material than the cream polish. Use this for badly faded decks first and follow up with the cream polish. Apply both these polishes with a small cloth in the shade and polish off promptly. Rotate cloth often – you’ll see the colour the polish is removing on the cloth. Don’t worry, your gelcoat should be thick enough to spare a few microns!

Deeper scratches in the gelcoat may need the use of ‘wet and dry’ paper prior to using the above polishes. Usually dark grey in colour, they are designed to be used with plenty of water to ‘float off’ the spoil.  Mask up the area to be sanded first and then start with perhaps a 320 grit paper, working in small circles with EVEN pressure. Stop often, wash off the spoil and look at your work. Then go to 600 grit and repeat. You can then go to the polishes to complete the job. With wet and dry, the higher the number, the finer the grit. You can get 1200 and even 2000 if you want to but you’ll be there for quite a while – they are very fine papers.

If you don’t have an ‘even’ finish and you can still see scratches after you’ve finished, go back a step or two and sand or polish some more. Piece of cake.

The Keel Line

The keel line cops the most abuse. Over time you may have to put some material back instead of sanding it off. No problem.

Mask up the area to be covered. Sand well with a coarser grit DRY sandpaper. Keying the surface is vitally important. This will give grip for your covering and also remove any polish residue – nothing will stick to the polish!

You should now wipe the sanded area with acetone solvent. It will dry in a few seconds.

Here we need to explain the difference between gelcoat and flowcoat which is what we’re going to use here. Gelcoat is designed to cure in the absence of air such as in a mold beneath layers of a laminate. Exposed to the air, it will remain tacky and un-sandable for days. To exclude the air, we can cover the repair with non-stick kitchen cling wrap or, more simply, add a solution of wax-in-styrene. The gelcoat (now called flowcoat) can be applied as you would a thick paint and it will cure fully for sanding in an hour or two.

If you apply it too thickly, you’ll have quite a sanding job to do to sand it smooth.

Deep gouges in the deck or hull can be repaired easily with flowcoat. Get the repair area level – sand the repair area, wipe with solvent to remove all traces of wax, etc, maybe feather the edges of the hole slightly. Overfill with flowcoat, working it in well with a toothpick or similar. Sand and polish when cured – that is, when your fingernail doesn’t mark the flowcoat!

For repairs in coloured gelcoats other than white, you should try to use gelcoat from the same batch as the boat was made from for a perfect colour match.

Why Polish And Repair Every Little Nick?

I do this for two reasons:
Firstly, smooth boats are faster than scratched boats. You probably won’t notice a drop-off in speed as your boat gets scratched over time but the difference is there. Over a full day’s paddle or a long expedition, there will be a real difference in effort.

There is a formula for the relationship between hull ‘roughness’ and speed. Basically, it says that the faster you want to go, the smaller the surface defect is that will affect your speed.

Secondly, when doing this sort of maintenance, you look closely at your boat and find things like star cracks from that last gauntlet, etc that you might otherwise miss.

Gelcoats, wax-in styrene, pre-mixed flowcoats and all resins are all available from the major suppliers. You may have to buy a few kilos though. Check the Yellow Pages.

Holes Right Through!

You may be able to patch these temporarily with duct tape – the sea kayaker’s ‘repair-kit-on-a-roll’, but you will have to repair the hole before the next paddle.

How you do this will depend on access to the inside of the hole.

Firstly, you need to clean up the hole using really coarse grit paper and maybe a knife. Roughen the inside of the laminate and the gelcoat edges of the hole too, and wipe with solvent. You should plan on the patch being half as big again as the hole.

If you can get at the inside of the hole: tape up the outside and apply the patch of layers of reinforcement wetted out with resin from the inside. You could also apply gelcoat before the patch – this might save some work later. Using brush and preferably a small roller, work the air bubbles out of the patch. Remove the tape when cured, sand and apply flowcoat. Sand and polish.

If you can’t get to the inside of the hole to apply a patch, you will have to work from the outside. Prepare the edges in the usual way. Cut a piece of cardboard  bigger than the hole. Fix a piece of string or fine wire to the middle of the cardboard, thread on the required pieces of glass mat the same size as the cardboard. Wet them all out with resin on the cardboard, then bend the cardboard piece through the hole and pull back into position with the string. Fix somehow until cured. You may need to use 3 or 4 pieces of string if the patch is in an area of concave shape. Gosh this is fun and games isn’t it! Plan your work before you start or you can end up in a real mess with this! Fill the outside with flowcoat, sand and polish and you’re done.

That’s about it. Some great little aids to all of these steps are:

  • masking tape
  • stiff cardboard (sometimes called pasteboard)
  • hot glue
  • Glad Wrap (use the good stuff only)
  • plasticine

Good luck and happy repairing!