epoxy

[Jack Wood]

I am thinking of making a small john boat and will be using plywood. The plans I have call for using epoxy to seal the plywood and also the seams to make it waterproof. My question is, having never worked with the stuff other than the small tubes you get for repairs, is this as easy as the plans make it look? It calls for a gallon of
105 epoxy,
#405 Filleting Blend
# 423-6 graphite powder for the bottom(mix in the epoxy to make the bottom slick)
#407-5 low density filler
minipumps
Geez a gallon of the epoxy is near a 100 bucks and all of the rest will no doubt rack up the charge more. You can buy a really nice little puddle boat for $500, but of course if I'm here it's because I want to make it myself.
Bottom line is if using the epoxy is really tricky, I'd hate to sink in the middle of a pond Or is the learning curve easy to take? THANKS!

[Cecil Arnold]

Call me tacky, but I like the stuff. It generally has better open time than PVA, and you can adjust that by using slightly more or less catalist. The various fillers and micro baloons enable you to build-up, fill voids etc. Many high performance homebuilt airplanes use a couple of coats over 1/4 marine ply as a sealer/skin coat that holds up to 250 mph rain, etc. so if applied properly it should leave you high and dry in the lake/stream.

[Jamie Buxton]

Epoxy is expensive, which is why lots of fiberglassing is done with polyester resin. http://www.shopmaninc.com is one source for both polyester and epoxy. I notice that their price for West Systems epoxy is somewhat less than your quote, and their own brand is even less.

If I was building a plywood boat, and was already committed to using resin for waterproofing, I'd add fiberglass cloth, at least over the seams and at rub points. For almost no increase in weight or cost or hassle, you get a much much stronger boat.

[Kurt Loup]

Jack,

I have built 2 canoes and 4 kayaks, so I have a good bit of experience with epoxy (photos on my webpage http://www.loup-garou.net). On the first boat, I used West System. I switched to Raka http://www.raka.com epoxy for the other boats due to the lower cost. Raka was one of the cheapest epoxies on the market, but they went up a bit so I gave the US Composites epoxy a try. I like it as well as the others. I purchased the 2-1 slow hardener. I've never tried polyester resin, but from what I have read, the only benefit, if any, is the cheaper price. The fumes are supposed to be pretty bad.

Kurt

[Richard Allen]

Epoxy is mostly a no-brainer. Mix the right propotions and you are good to go.

When you buy the stuff in large quanities make sure you get a set of pumps as well. THe pumps make getting the right proportions as simple as pressing down on the pumps.

Don't mix to much at a time. Epoxy cures by the chemical reaction it makes. Part of that process is that the reaction produces heat. If you have a few ounces of epoxy mixed up when it starts to cook there will be a LOT of heat generated. This is NOT a good thing. So mix in small batches and spread it thin.

If you can warm the surface that you are putting the epoxy on there will be greater penetration of the epoxy. Just exposing the wood to sunlight in a still air can be enough heat to aid in the absorbtion.

"WET" the surface before thickening the epoxy. This is to say that a thin coat of epoxy should be applied so that the epoxy can soak into the wood before applying epoxy with thickener added.

If the epoxy hasn't fully cured (several hours) the applying additional epoxy will form a molecular bond. If you apply additional coats of epoxy after the first coats have cured then you need to rough up the surface so a mechanical bond can be formed.

To Recap:

Mix the right proportions (pumps help a lot)

"WET" the surface (with a thin coat of epoxy)

Warm the wood before applying epoxy.

If additional coats are needed apply within hours of the previous coat.

Wear gloves

Mix in small quanities.

[Mark Singer]

I use West Systems for a lot of projects....it is very consistent and the bond is strong. If your joints are not perfect it still works. A gallon seems to last a long time. I use both the slow and fast catalyst depending on the project. It seems as it ages it seems to "go off" faster in the mixing cup. I don't know why? It is waterproof and almost a must for exterior projects.

[Michael Sloan]

I have used both West Systems and System 3 epoxy to build boats, and both worked great. I have also use vinylester and polyester resins. Use the epoxy. The extra strength is worth the cost, also you are much less likely to really screw up a batch of epoxy than a batch of polyester resin.

I built a boat a few years ago out of a local brand of epoxy, that turned into a major problem (had to raise the shop temperature by a lot during the winter to get it to kick off). So I would use one of the major brands, (West Systems, System 3) at least until I new for sure what I was doing.

Most people screw up a couple of times before figuring out how to use the stuff. Usually happens because you mix too much and it gets too hot and kicks off before you are ready for it to. So mix small batches.

Also, mix thoroughly. Keep stirring for longer than you think you need to.

Also, epoxy can be a skin sensitizer, so use gloves, and use a respirator when sanding.

Good luck with the boat. As someone else said, you should cover the plywood with a layer of fiberglass if you want the boat to be durable.

[Jack Wood]

Thanks for all the info! I am going to go ahead and build the boat and use the epoxy. Thanks for the link Jamie, and Kurt that is a beutiful job you did on that kayak! I'll let you all know how it turns out.

[Dave Richards]

If its not too late, check out Raka for your epoxy. I bought mine from them and found it to be excellent. The mix is 2 parts resin to 1 part hardner making the mix ratio easy to get right. Price was better than the other common sources, too.

http://raka.com No affiliation, just a satisfied customer.

I lost track of how many gallons I've bought from them but I've done two boats and several miscellaneous projects with it.

[Lynn Sonier]

I like the Clark Craft Epoxy and it is not quite as expensive. Try clarkcraft.com. I used their epoxy to build a 10' dinghy and liked the way it works. If you allow it to set overnight, there is no blush for you to wash off.

[Jack Wood]

I went to the ClarkCraft site and it is a really good one! They are really in to "build your own". I also went to the Raka site and it too is good. Thanks for all the info!

[Byron Trantham]

Kurt, what a spectacular boat! Man I love the form and finish! It must take a boat load of patients (no pun intended) to build.

[Kurt Loup]

Byron and Jack,

Thanks for the compliments. Kayaks take me about 6 months or so to build. The wood work is easy. I can strip it in a couple weeks. The fiberglass and epoxy work takes the longest time. The last 10% of construction takes 90% of the time.

Kurt