Epoxy Work

by Bernd Kohler - The Netherlands

Boats can be built in a wide range of ways. From the traditional wood construction to the new infusion techniques. For a newcomer to boat building, it can be a bit bewildering.

As some of you will know I am a strong a proponent of the plywood/glass/epoxy system, because any handyman who can handle a screwdriver, a saw and a brush can build a boat. Epoxy is the most versatile material to put the wood pieces together and by adding glass cloth, thickeners on strategic places end up with an almost maintenance* free boat which can give you many years of pleasure.




Some builders are not interested in a long lasting boat and are happy to trow it away after one or two seasons, so be it. Almost on a daily basis new glues, coatings and paints coming on the marked that claim that the are equal or better as Epoxy. Time will tell. By the way, the rudders on my Cataproa prototype are from a 25 year old DUO 425.

So what are the drawbacks of epoxy?

Old claim, the hardener is toxic. This period is over, see for instance the new Epoxy sold here at Duckworks and some companies in Europe who produce them too.

I have worked since 1967 with Epoxy and never had a problem**. Paramount is to work clean and in a well ventilated environment. By the way, if you get some Epoxy mixture on your skin, do not remove it with Acetone, MEK or any other chemical product – use vinegar*** and wash off afterwards with soap.

The most heard complaint, my epoxy stays sticky, doesn’t get hard or doesn’t cure. Obviously, the mixing ratio was incorrect. The amount of component A and B must be right, because when mixed together the form new macro molecules form the “epoxy”. If one component is to much in the mixture it can not “connect” because it misses the other part, so the mixture can not cure. This is the most common failure. An easy to avoid one though. Use a balance which can be made for pennies. No calculation necessary. When the balance is in equilibrium the quantities are correct. No calculation needed, nothing can go wrong. Of course the melange has to be properly stirred.

Many find the curing time of about 24 hours a hindrance, boring. Okay this is a matter of organization. You can have a beer and an other etc to watch the curing process, or you can start with an other piece, for instance with a rudder or whatever part has to be made next. An other often heard complaint is, I get runners and sackers when I apply epoxy on vertical surfaces. This can happen, one epoxy is more prone to this effect as the other. This can be lessened with some additives. But it will not happen when the pieces are coat horizontal. And this is the main reason for this sermon.

All my instruction manuals start with, “pre-impregnate the plywood panels.” But almost nobody is doing it. It is boring work and many think a waste of the expensive Epoxy.

A customer was showing my his way to coat a plywood panels in the shortest possible time. He uses window cleaners instead of a foam rollers. Normally, you need 80 grams of Epoxy per square meter. He needs only 60 grams. Besides, when you use a roller, you waste about 200 grams of epoxy which you can not squeeze out. So in the end, you use more epoxy instead of less. The best part, coating a plywood panel with the window cleaner takes only 7 minutes. This is significantly less time than with a roller. Here a video from the procedure on a plywood panel and on bulkheads. Watch the action on the plywood panel and imagine doing the same length with a roller.

 

7 Comments

  1. well stated!

    i try to always have more than one project/step to do at any given time, which allows me to keep moving fwd while the POX cures

    window squeegies or auto body BONDO spreaders work quite well and when the POX is cured just flexing the tool will release the cured stuff and the tool can be used again

    written descriptions are good, written descriptions W/ pics are better AND written descriptions W/ MOVIN PITCHERS ARE WAY MO BETTAH

    THANKS

    sw

  2. I have used this technique and it is superb. Best results include pressing hard on the spreader on the first coat to help force the epoxy into the grain. Don’t try for too much thickness on the first coat. As Bernd suggests, the goal is to impregnate the would more than coat it over.

  3. Many complain about all the sanding and more sanding required with epoxy coating. That is just not necessary and mostly caused by the uneven or lumpy nature many get in the first coat. That roughness results from raised wood fibers and uneven soaking of the first coat. I can almost completely avoid this by squeegeeing on a very thin first coat, as thin as possible. By pressing hard to fill surface grain, the fibers are trapped and there is not enough resin to cause them to swell or float. After cure, sand lightly with 220 grit and the result is a very smooth surface to accept later coatings that will be smooth enough without any aggressive sanding.

    This first coat method can also help prevent rupture in extreme torture of compounded plywood by spreading the stress over larger areas of surface by preventing point loading of the most critical or weakest area.

    • I use squeegees made by Thalco, They are rubber and heft eough to allow considerable force in spreading resin. They can be renewed by cleaning or sanding a new edge so that mine are about 25 years old. They are bought in any length you need and price is by length. A professional tool that is far better than plastic stuff.

      • Hello Tom, years ago I used squeegees by Thalco. Haven’t been able to find a source today. Where do you get yours please, thanks. Mike

Leave a Reply

Your email address will not be published.


*