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Is there an alternative to epoxy resin for sealing a plywood boat? Answered

 I am planning on building a version of the CC14 or NC16 from bateau.com. I would like to keep my costs down on this project as I just bought a car, but would still like to build this boat so I can get out on the water along with my wife who has a kayak. I was wondering if I could just use epoxy/fibatape combo to seal the seams and add strength where the panels come together, and then just use something like rubberized roof sealant (like used on the CozyBoat by TimAnderson) to seal the rest of the plywood from rot. Anyone have any ideas on this?




Best Answer 8 years ago


 I originally considered paint, and after discussing this with some tech ed teachers I know, they suggested that paint would not be durable enough. If I scratch it on a rock, no more paint to protect wood. :S

Paint is the traditional solution--been around for generations longer than epoxy.

I've built a couple boats. You'll find a lot of debate over epoxy "encapsulation." May people feel it just leads to "checking" on plywood--particularly Douglas Fir (which is great boat building wood, BTW.)

And at the most, epoxy alone just penetrates a millimeter or two into the wood. A scratch penetrates that pretty easily. If you completely "glass" the hull, it'll increase the weight by 1/3 to 1/2.

And most epoxy has minimal UV resistance...so people have to paint it anyway...

The secret to wooden boats is routine maintenance. If the paint is scratched, you repaint it. If you start with "durable" wood and good fasteners, preferably bronze or SS, you'll be fine.

It is marine-grade ply?


 Exterior grade fir is what I was thinking...

"exterior" sounds like "waterproof". It may look better with marine yacht-varnish, and you should really use a product which is designed for the conditions, but paint (as a one-word best-answer) would probably be as good.


 Spar urethane and paint

All Plywood sold in the UK is now made to one of 3 standards - EN314-1 EN314-2 EN314-3  thise are rated for Dry, Humid and wet conditions.

EN314-3 is what is normally sold as exterior quality ply and the glue used is water proof. Marine ply is high quality water proof ply with a guarantee  that there are no voids in the inner layers. Also generally has a better surface finish as well.

All that said  I have a 10 foot sailing boat made from EN314-1 (interior quality) about 9 years ago. Taped seams with fibre glass tape and polyester resin (i.e. normal car repair fibre glass materials, painted with a normal gloss paint for exterior wood. It is still water proof and works well.

I have also rebuild sailing dingies with standard interior faced ply well varnished on both sides with good results.

Even standard household emulsion paint (USA Latex paint) will defy the elements for a long time especially if you put a coat of varnish over the top.

No matter what you do a painted boat will need repainting periodically.

For the Plywood try to get a ply that is even thickness of veneer throughout. IF you can afford it get Birch ply as there will be fewer voids and more even thickness of veneer.

If  your considering a canoe have a look at gaboats.com/boats/ these are not hard to make once you have made the strong back and can be made with strips of  6 mm plywood rather than solid wood - The bracing need not be exotic Kevlar either but packing strapping will do the same job.

For a cover ballistic nylon gives you a slightly heavier but stronger cover although I have plans to try Tyvek and see how it goes.


8 years ago

As a contractor I have seen many a case of elastomeric (rubberized) roof coatings gone bad. Once there is a penetration made into the coating from a scrape or sharp object, a minute amount of water can get under the coating and then, when heated up by the sun, vaporize, causing blistering and separation from the deck and the resultant failure of the waterproof membrane.
Don't use it on a boat. Sooner or later, it will fail.
Presuming you are wanting to build a canoe that will last for many years, I would suggest that you not scrimp on the materials. If you're just looking for a season or two's use, The elastomeric coating, if properly applied and maintained, should work for a couple of years.