In 1994 I built a glued clinker dinghy which I described to the North-west winter meeting in 1995. I promised at the time to write up my experiences with epoxy resin glues. For those of you not familiar with epoxy glues: they consist of a liquid resin glue and a hardener which when combined in the right proportions set to form a hard solid. The mix can be used straight as a protective coating for wood or mixed with various powders to form a gap-filling wood glue or a variety of fillers.

I am not going to give a ‘how to do it guide’ as the manufacturers supply a deal of helpful literature to that end, but rather a ‘consumer report’:

1. Some of the advertising material put out in the past has tended to suggest that epoxy coating saturates the wood throughout and effectively preserves it resulting almost in a plastic boat. This preservation treatment was one factor which helped to sell me the product. In practice the treatment does not saturate the wood in depth. The epoxy forms a hard surface coating which penetrates the out layers of the wood only. The coating is highly resistant to abrasion but epoxy without fibre reinforcement is brittle and will shatter on impact from a sharp object allowing water to penetrate to the wood beneath. Also the glue is expensive if you start covering large areas.

2. Another claim sometimes made for this coating is that it can be varnished over to give a wood finish. The thought of a glue which would not show through varnish despite my indifferent cleaning up was attractive indeed! However only pure epoxy is clear. The wood glue version is white, like wallpaper paste, and the fillers come in a variety of colours including one, low density, which in its unset state strongly resembles chocolate whip. Children beware! Coating with straight epoxy imparts a honey-yellow colour to the wood. This is pleasant on pine but disappointing on mahogany where it instantly produces the effect of many year’s fading. Equally annoying; the epoxy-glass tape joints in the deck show up as yellowish strips against the richer colour of the surrounding ply.

3. Another problem is ‘amine blush’; a whitening of the surface of the epoxy due to adverse setting conditions. In theory this can be cleaned off; in practice it is not that easy to see until you have varnished over it, when it shows up very clearly. The same is true of smears of wood glue left around joints. There went any aspirations I might have had of competing in the Wooden Boat Show boatbuilding competition.

4. One merit of epoxies is their gap filling properties, i.e. their ability to bridge the holes in ill-fitting joints and so give the less handy woodworker a boat that is still waterproof. Indeed it is claimed that glued clinker planking does not need the underlying plank to be bevelled at all in order to make an effective joint. I could well believe this would work but I bevelled mine roughly, for appearance sake and to economise on glue.

5. Cleaning up: when set the wood glue is extremely hard and some of the fillers are harder. It is therefore important to remove as much as possible of the surplus glue, squeezed out of joints, before it sets. The glue is too expensive to waste so each larger job needs to be accompanied by a range of smaller ones on which the surplus glue can be used up. Cleaning off the remainder once set is hard work… and requires care else your efforts are more likely to grind away more of the surrounding wood than the glue. I ended up using metal-working files on the outside of the boat. The inside was inaccessible during planking up so that large lumps of epoxy remained to be removed afterwards. These had to be ground off using a Black and Decker with an emery wheel. I soon found out that attempts to cut glue off with a mallet and chisel resulted in lumps of glue coming away intact, with pieces of hull still attached to them.

6. Coating with glass cloth: an even tougher finish can be produced by coating wood with a layer of woven glass cloth soaked in epoxy. I used this technique on the two broad garboard planks of the hull. It was easily the most stressful part of the job. Two methods of application are possible; apply resin on top of dry cloth — or dry cloth on top of resin. I chose the latter thinking that it would be easier to avoid trapping air bubbles. You would think that spreading a flat piece of cloth over something the shape of an upturned saucer would result in the cloth fitting well in the middle, but with fold radiating round the sides. Not so; the sides fitted beautifully leaving a huge crease athwart the centre of the hull. All this work has to be carried out within a setting time of about ten minutes measured from the time you mix the first batch of resin. I smoothed the cloth this way and that, but could not shift the crease. So faced with a soon to be ‘permanent wave’ I cut the cloth across with a craft knife and folded the edges down over each other. Happily the joint does not show through the paint.

7. Safety: the harder is an irritant but I had no problems using the recommended kit, i.e. goggles, disposable gloves, barrier cream etc. Resin removing cream coped when the gloves tore, usually because I had clamped them to the boat.

I did have a little fun in another direction however. Epoxy sets by a chemical reaction which is accompanies by the evolution of heat. The rate of reaction and hence heat production, increases with rising temperature; so you have the potential for a catastrophic runaway if you are not careful. This occurred only once when, working in winter, I absentmindedly held the pot close to the heat lamp I was using to warm the work. I noticed that the pot was getting hot and apparently ‘steaming’. Then realised that the steam was smoke and shot out of the workshop like the proverbial scalded cat. Apart from losing that mix nothing more spectacular occurred, no bursts of flame… but a sobering experience all the same.

Conclusion

The mechanical properties of the glue seem to be all that is claimed for it; strong and gap-filling. However producing a beautiful varnished epoxy glued boat is not easy and required considerable care. I am still using the glue for other marine jobs and there have been no problems with the boat yet.