Wooden
Boatbuilders'
Trade
Association

Using Epoxy in Traditional Construction

by JAMIE CLAY

I have seen a teak-on ply deck laid with red lead putty as the bedding between the two, and a 5 inch diameter wooden rudder post with the blade built out with epoxy-glued sections to the back of it with no other fastenings. The rudder blade, a few days after launching, floated off down the river, unnoticed by the owner. I don't know the fate of the teak and its plywood sub deck, but I don't hold out great hopes. Mixing the old and the new can be dangerous, and if it is to be of benefit, it must be done with an understanding of how both work.

You sometimes hear a builder proudly announcing that not a single drop of epoxy was used in the making of a boat. That might be admirable in the making or restoring of a boat for a museum exhibit or a 'live archeology' exercise, but there is surely a place for epoxy and other 'modern' materials and methods in traditional boatbuilding. I'd maintain they can improve longevity and in some cases, strength. Anything that improves longevity also helps to justify our use of the world's resources in making a boat. If we can only say of a job "well it'll last me out", that's not ideal. We should be aiming to make and rebuild boats which will last at least as long as it takes to replace the trees we used to make them!

I have gathered a few instances below. I don't want to be dogmatic about it, because someone will always come up with a contrary opinion or case where it didn't work or something else worked much better. But if it starts a discussion, that would be good.

HULL PLANKING AND FRAMING

If you go over a carvel hull with a moisture meter, it will usually give a high reading in the area of planking butts and hood ends. This is often where deterioration starts - corroding fastenings, leading to movement, cracking paint, more moisture uptake, and so on in a vicious circle. On the last carvel hull I replanked, we epoxied the butts and hood ends of the planks as we put them on. Some people paint them, but the epoxy is much harder, seals the end grain much more effectively, and when you come to caulk up, resists the scuffing of the caulking process much better than paint.

Scarphs properly formed and placed in carvel or clinker work, have to have something between the faying surfaces. I don't see any reason why that something shouldn't be epoxy, rather than any other bedding compound. You might just as well have a strong adhesive and waterproof bond backing up mechanical fastenings, as mastic or luting or varnish.

I took some cracked sawn frames out of a 1910 yacht to replace them. Between the planking and the frame (bare wood to bare wood) was a thickish layer of moist dust and grit which had built up over the 100 or so years of the boat's life, the movement of the oak frames causing gaps to appear where dirt could get in, but there was no sign of decay - a tribute to well-selected and well-seasoned wood. More often this is where the rots starts, and you find the back of the frame or the face of the plank going soft. They might both have plenty of strength left in them, but if the faying surfaces are squashy, the whole boat will be working and the fastenings struggling to hold it all together. A heated discussion began in Maldon, when one builder, replacing old sawn framing with laminated framing in a class of 35ft yachts, started gluing the new frames to the planking. A lot of people including me, thought this was an epoxy mix too far. But 20 years on, there is no sign of any problem at all. The boats are all raced hard, but well looked after. The glue must contribute significant extra strength as well as keeping moisture out of a place where it can fester and start trouble.

I have subsequently heard of a Dragon class yacht refitted here which had planking glued to the frames from new - with Rescorcinol glue - dating from the 1950s; still going strong.

You have to evaluate the benefits against the possible draw-backs. The 1910 boat referred to above, sank in an accident, and was under water for two tides. When she was raised and cleaned out, a week or two of fine summer weather caused her topside planking to cockle outwards horribly. The sun and free movement of air externally meant the outer surface (though well-painted) dried much more quickly than the inside (which in part was kept damp by all that muddy, dusty stuff between frame and plank). Everything settled down eventually, and the next season's paint job put her back to rights. But how would that planking glued to the frames have faired? Would the swelling and drying cycle have overpowered and broken the glue joints? Teak decking is often bonded to the substrate, and caulked with something flexible, so that the upper face of the plank can swell and contract, while the lower face is held immovably to the ply (or grp or aluminium, etc.). So maybe the hull planking would be OK - as long as it is not too thick, and as long as the framing is laminated and therefore more stable.

One common mistake among epoxy-happy boatbuilders is to glue together components that are of too great a section. It is difficult to come up with a 'rule' here, but we soon get a feel for chunks of wood (some types more than others, obviously) which are going to do what they want, irrespective of whether we glued them to some other piece of wood or not. Once the glue line has failed, often the situation is worse than if the two components had been joined on mastic of paint.

ON DECK

When it comes to beads, quadrants, rubbers, and that sort of thing, you often - very often - hear the die-hards say "you shouldn't glue that, it should be set on mastic, otherwise, what happens when it needs replacing". My reply to that is that if something needs replacing, it is usually for one of two reasons - either because the water has got behind it, or because it got broken. If the water got behind it, it is usually because it wasn't bedded properly or it moved on the bedding - which it wouldn't have done if it had been glued, - and if it got broken it doesn't matter if you mash it off with a chisel or planer anyway! One of the great advantages of epoxy over Rescorcinol or Cascamite types (urea formaldehyde) is that it softens with heat. You can usually 'undo' epoxy bonds with the application of heat from a heat gun.

I put a new ply deck on a Folkboat and set a glass cloth in epoxy over it, butting the cloth against the cabin sides (solid mahogany) and running an epoxy fillet over it in the corner. I then made up mahogany quadrants, knocked the back corner off them, to house the fillet, and glued and screwed them into the deck/cabin joint over the fillet. A (embarrassingly) few years later, the owner, - admittedly notoriously neglectful of his boat, - rang to say the quadrants were going rotten. I am ashamed to say I had used some unidentified 'pink' wood, and it certainly was rotten. In places, I could just scrape it all away, leaving the glue that had glued it to the deck and cabin, and the fillet in the corner, which was perfectly intact and keeping the joint completely waterproof still. In that instance, using epoxy to glue the quadrant rather than bedding it on mastic, had just about rendered the quadrant itself redundant, and made that area of the deck neglect-proof!

I have only touched on epoxy glue here, begging lots of questions, and not even mentioning sealant/adhesives such as Saba and Sika produce. They hold large chunks of aeroplanes together these days, as well as helping to stop the constituent parts of the bottoms of Hacker and Chris Craft type speedboats from rattling to bits.

There are always new products coming onto the market to tempt us with promises of wonderful problem-solving properties. It is crucial to get to understand how they work, and in each case what you are asking them to do. And of course, the one characteristic they all have in common, is that they are 'fussy', the products of precise chemical engineering, and you ignore the instructions for mixing, surface preparation, temperature, etc., at your peril!

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