Michael Storer Boat Design 

FAQ - Are 1 to 1 (1:1) epoxy mixes OK for boatbuilding?

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Most quality boatbuilding epoxy manufacturers have a structural boatbuilding product. They normally are "high solids" boatbuilding epoxies that have uneven resin to hardener ratios (2:1, 3:1, 4:1 or 5:1) which you have to add powder to make a glue or filleting mix The same companies often produce pregelled products that are mixed in a 1:1 ratio for more general woodworking - that don't require extra powder Just like good old araldite. I keep being asked whether these 1 to 1 pregelled epoxies are OK for boatbuilding applications. 1:1 Epoxy mixes are a compromise My understanding is that one to one resin ratios are quite hard to achieve and require some serious compromises in the strength of the cured epoxy. So if using epoxy for a strength critical application (boat, aircraft etc) stick to the uneven ratio standard resin and add the powder modifiers. This is the most flexible use as it is easy to adapt the mix to the timber being glued. eg Glueing a scarf and adapting for the absorbency of the end grain Laminating on the flat where the mix can be a bit more runny so it moves into any gaps more easily Making a thicker mix when working on a vertical surface Making up a peanut butter consistency mix when filleting One Answer won't resolve all problems Taking the example of dealing with end grain - with the normal boatbuilding epoxy it is normal to make the epoxy/powder mix a little bit more runny - or even better mix up resin and hardener, brush on end grain. Then add the thickening powder to the rest of the epoxy in the pot to make the gluing mix and apply to the surfaces of the scarf - then clamp. With a pregelled 1 to 1 mix it just ain't possible. Applications for 1 to 1 Epoxies - where stiffness is critical but strength not so important But the 1 to 1 makes a lot of sense for furniture and other non critical applications as it is so convenient - it's gap filling and stronger than just about any other woodwork glue. I used to be an agent for one of the major Epoxy manufacturers in Australia - and they suggested furniture as an ideal application for their one to one product :-) But the point is that the standard 2 to 1 resin/hardener systems plus fillers are much, much stronger and more adaptable in use than the 1 to 1 pregelled systems. So with boats - stick with the former - boats are actually under REAL load so have to actually be strong. Furniture is designed to feel STIFF - not deflect in use. But it is really WEAK. Give me a piece of furniture and I can pull it apart with my bare hands - NO PROBS - rip legs and backs off chairs - no worries, pull corners of sofas apart - woooohooooo. But try the same on any component of a boat - not a chance. So the glue has to be up to spec. By all means use either the 1:1 pregelled glues or the full "mix yourself" epoxy systems for furniture - both are strong enough for that use. But ONLY use the full resin systems on boats. A final argument I am pretty sure that most epoxy companies would love to be able to offer a single prethickened product with an easy 1 to 1 mix - but they don't - not one of the serious companies. That indicates that they don't think they work!