Montana Riverboats Test Domain Roadkill

Part Two Working with WEST SYSTEM Materials

 Part Two Working with WEST SYSTEM Materials 


Tools for applying WEST SYSTEM resin include a 1.5" or 2" bristle brush with a wooden handle, 1.5" to 6" putty or drywall knives, and foam paint rollers of various sizes. Clean your tools regularly with WEST SYSTEM solvent or acetone. (Caution acetone is flammable). Keep the brush and the smaller putty knives in a can filled half-way with solvent, and keep a lid on the solvent can to keep the solvent from evaporating. Hardened epoxy can be burned off putty knives with a propane torch. Use a wide, flat container such as a roller pan with a plastic liner or a plastic dishpan for mixing epoxy. A wide container dissipates the heat created by the reaction of the #105 resin with the #205 hardener. Heat can build up in a small container creating a chain reaction that will harden the resin in a matter of seconds. Overheated resin that is setting up fast does not penetrate or adhere well to wood. Whenever a chain reaction does occur immediately discard the overheated resin and start again. Use rubber gloves at all times when handling epoxy resin. Epoxy resin is a skin irritant, and some people develop allergic skin reactions to it. You may also want to wear a good respirator with activated charcoal elements designed for organic vapors. Always wear a dust mask of some kind when grinding or sanding epoxy- fiberglass. Cheap, disposable vinyl or latex rubber gloves are handy, but I prefer heavier, chemical resistant gloves that can be washed in solvent after each use and reused indefinitely. Chemical resistant gloves can be purchased at most janitorial supply houses.

Gluing, Filleting, and Fiberglassing Procedures 

Follow the manufacturer's instructions for using WEST SYSTEM products but also read the following supplementary information. For every gluing, filleting, or fiberglassing process, you will use WEST SYSTEM #105 resin mixed with #205 fast hardener. The ratio is 5 parts resin to 1 part hardener. WEST SYSTEM mini pump dispensers automatically measure the resin and hardener in the right proportion. One squirt of resin mixes with one squirt of hardener. The mixture of resin and hardener will be referred to as "resin" for the duration of these instructions. #105 resin is never used without its corresponding component of hardener, so it is now understood that the term "resin" will mean the proper mixture of resin and hardener.

Priming the Pumps 

Unscrew the caps from the #105 resin and the #205 hardener and replace them with the corresponding mini-pumps. Hold a Dixie- cup or other small container under the hardener pump and push down repeatedly on the pump. Let the plunger rise up slowly by its own spring-loaded power. Once the pump stops spitting air and is completely primed the hardener collected in the Dixie cup can be returned to the hardener can. Repeat this process for the resin pump, using a fresh Dixie cup. Always mix the glue thoroughly. This is the number one most frequently encountered problem beginning boat builders have. If you do not mix the resin well it may never harden properly.


Always wet out both sides of any joints to be glued with resin as a first step. Usually one wet coat is enough, but for porous woods and end-grain, you may need a second coat. The wet-out surfaces should look wet. After wetting out the surfaces, mix a second batch of resin and thicken it with #403 microfibers until it is the consistency of sour cream or yogurt. Apply the thickened mixture to one side of the joint to be glued. Clamp the joint until the glue is hard. Hardening times vary considerably with temperature and humidity changes. Immediately clean up any squeeze-outs.

Filleting and Puttying 

Filleting is the rounding out of inside corners to reinforce the joint, and to produce a smoothly rounded corner prior to fiberglassing. Use a mixture of 60% #407 micro balloons, thirty percent #403 microfibers and ten percent #406 colodial silica for all puttying and filleting operations. (This mixture works well for me, but don't be afraid to do a little experimenting. Epoxy resin is strong, versatile stuff, and you can get satisfactory results from a variety of thickeners.) Wet out the area to be filled. Mix another batch of resin and thicken (with micro balloons, micro fibers and colodial silica) until the mixture is the consistency of thick peanut butter. Use a physician's tongue depressor (or cut a rounded tool from plywood) to apply and smooth the filleting. Apply the mix thickly in the area to be filled. Then smooth repeatedly with the depressor to form a smooth rounded shape. Press down hard on the filleting tool to squeeze out the excess putty as you form the fillet. Immediately clean up squeeze-outs with a putty knife. For puttying to fill up dings, use the same mix as for filleting.

Scarfing Plywoo

Full length plywood has become impossible to find. Even if you can find it the price of the plywood is high, and so is the shipping. It's better to buy plywood in 4x8 foot sheets and do the scarfing yourself. To make a single length out of two shorter pieces, you make two slanting beveled edges at one end of both sheets. Then you spread glue over the joint and clamp it together.

Scarfing reduces the overall length of the two sheets by approx 1-1/2" This is OK. Side panel layouts are made from front to back. The transom ends up at the rear end of the panels, attached to back end of what the scarfing process gives you. Later on in the plans, when I refer to 4x16 plywood, I really mean 4x15'x10-3/4"'s not much of a difference, and 4x16 is easier to say (and write).

Note too that AA marine plywood sometimes comes a little longer than 8'. In that case, you might well end up with a full 16' It doesn't really matter. In a later step, when you layout the side plywood for temporary rib stations, start the layout for both side pieces from the same end: front or back end, take your pick. Just make sure you don't start measuring from the front on one side and then from the back end on the other side.

West System sells the above tool at many of its retail outlets. Instructions come with the tool. I bought one of these scarfers nearly 20 years ago, and still have it. But I do now prefer my own home made scarfing tool. The literature that comes with this tool claims (when used with a 7-1/4” circular saw blade) it will successfully scarf plywood to 3/8" thick (approx 9mm in Okoume). But it works fine for 1/2" too. To scarf 1/2" plywood, use a new, full-diameter 7-1/4" blade (not sharpened down to a smaller diamter) and then be prepared to sand or hand plane a small ridge of wood approximately 1/2 a surface ply thick, where the saw blade doesn't quite make it through the panel. (These plans don't call for using 1/2" plywood anyway, I just added that for perspective). After making any such scarf cut, build up a long flat working surface with 3 or 4 extra-straight 16' 2x4's layed over saw horses. Then put scrap plywood or chip board over the 2x4's and then cover the chipboard. Then make the scarf cuts. Then put the panels aside temporarily. Then cover the chipboard with visqueen. Then lay the gluing panels on top of the visqueen. Wet the scarf joint with unthickened resin. Then mix up some standard gluing putty with resin and micro-fibers and cover the face-up side of the joint. Press the panels together and align one 16' edge with a string line. Then drive drywall screws right through the still wet scarf joint, down into the scrap chip board below the visqueen. Back the screws out 4-8 hours later. That's it! You now have full length plywood. Ok, now we need to talk about plywood and what to buy. The materials list (in part- one) lists 2 4x8x1/4" panels as needed to make the sides (or two 4x8x6mm okoume, or two 4x8x5mm sapele...sapele is stronger, so the thinner panel is ok). To make the side panel, you follow the above scarfing instructions to make one 4x16 panel. To do this, you make a pair of matching scarf joints at the ends of two 4x8 panels and glue the two together, end-to-end. To make the bottom panel takes a little more explaining.

The Honky Dory is wide boat. It's 56" wide in the middle, which is (obviously) wider than a standard 4x8 panel. Why? The extra width is a godsend when rowing. The Honky Dory is extra-stable. Fishermen can walk around in the boat, change ends and even sit a little off- center in the boat without problem. The Honky Dory breaks big waves like an arctic ice breaker, and yet it holds very well and it turns on a dime. The wide bottom makes it one of the best all-purpous fishing boats ever built. Building it does require a few extra hours of elbow grease. For a long time, for each boat, I would buy two 5x10 panels I got from Harbor Sales in Baltimore or from Edensaw in Port Townsend Washington. (links are on the boatlinks.html page). The extra plywood left over after gluing the two 5x10s together went into seats and dry storage lockers, so nothing was wasted. This is still a good way to build, but 5x10 is hard to find now, and it is getting very expensive. Another approach is to limit the high cost of 5' wide plywood to one sheet of 5x8: IE you can build the bottom panel from one 5x8 and one 4x8. Edensaw usually has 5x8 panels in stock. To build this way, you scarf both 5' ends of a 5x8 sheet. Then you split the 4x8 into two 4x4 pieces, and scarf one 4' edge onto the center of each end of the 5x8. Finally Given the current cost of 5x10 plywood, the smartest way to build the Honky Dory bottom is from three sheets of 4x8.

Two full size sheets are scarfed together to make a 4x16. Lay this over top of a recently completed strongback and trace a pencil line around the edges, at the ends, where the panel is wider than the boat. Cut the corners off, with a skill saw set to 25 degrees. Now you have a bottom panel that fits nicely everywhere except the middle of the boat, where there is a long skinny, double pie shaped piece missing from each side, approximately 4" wide at its widest, tapering to a point at both ends, approximately 60" long. Clamp a straight edge on the bottom panel, on each side, so you can make a standard, sharply slanted scarf cut on each side, where the new pie shaped piece will go. Rip two full length pieces off the remaining 4x8 x 3/8 bottom piece you still have, that are 6" wide. Measure and cut those to the right length (approx 60"). Scarf one edge of each 6" x 60" piece and glue those onto the sides of the main bottom panel.

Now you can lay that back over top of the form, scribe one more time, and you now have an ultra-strong bottom panel, ready to install.


Fiberglass is a generalized term that refers to a wide assortment of woven fabrics that are layered and bonded together with various plastic resins. The best resin, in fact the only resin suitable for wood- fiberglass construction is epoxy resin because epoxy is the only resin that adheres well to wood. Fiberglass fabric is a woven laminate material that is made from glass fibers.

In its raw form, fiberglass fabric is very soft and flexible, and looks a little like white canvas. When fiberglass fabric comes in contact with resin, the fabric turns transparent and loses its white color. Fiberglass fabric is easy to work with, and can be used for every fiberglassing step in the construction of this boat. Other laminate materials that work well with epoxy include Kevlar, graphite fibers, and polypropylene fabric. If you are familiar with these other laminate materials, feel free to use them in place of the standard fiberglass fabric specified in these instructions.

Working with resin and fiberglass fabric 

In order to cover any piece of wood with a layer of fiberglass, start by rough- cutting the fiberglass fabric to the size needed, one to one and a half inches large on all sides. Wet out the wood surface with resin. To apply, pour the resin directly onto the wood surface and spread it with a four or six inch drywall trowel, or pour the resin into a roller tray and spread the resin over the wood with a foam roller. Lower the fabric onto the wet-out wood surface, and pull on the edges to get any wrinkles out of the fabric. A helper is particularly handy when lowering dry fiberglass fabric down onto a wet surface.

Two or more workers can lower the fabric into place with a minimum of wrinkles. Use a plastic squeegee or a 6" metal trowel to smooth the fabric. Use the trowel to stretch and tension the fabric, stroking the trowel from the center out toward the edges. Once the wrinkles are gone, apply more resin and smooth evenly until the fabric becomes transparent and disappears. But be careful! It is important not to use too much resin. Too much resin will float the fabric on thick puddles of resin. This weakens the finished fiberglass laminate. Use just enough resin to make the fabric transparent. Trowel any excess resin off the fabric to leave the rough, pebbled texture of the fabric showing on the surface. Avoid slick, glassy puddles of resin on the surface of the fabric. Some glassy spots are inevitable, just try to keep them to a minimum. On the other hand, don't use so little resin that cloudy- white areas remain in the fabric. Use just enough resin turn the fabric transparent, but not enough to float the fabric over thick, glassy puddles. Once the first wet-out coat has saturated into the fabric, you can quit for the day and then proceed with subsequent finish coats at a later date. Or you can wait two or three hours for the resin to become tack free, but not necessarily fully cured, and proceed immediately with one or more finish coats of additional resin. If you let the first wet-out coat harden completely, you must sand off any hard lumps of resin before finish coating. If you choose to go ahead and finish coat as soon as the first wet-out coat becomes tack free, sanding is not necessary. Use one to three finish coats as needed to obscure the texture of the fabric and to produce as glossy and as smooth a finish as you choose. Spread finish coats with a four or six inch drywall trowel, and then immediately brush out the lines left by the edges of the trowel with a bristle brush. To smooth out trowel marks that have already begun to set up, it may become necessary to dampen the brush with acetone or WEST SYSTEM solvent.

Paint Vs. Varnish 

The last step in the boat building process is to cover the boat with an ultra- violet shield--in other words to paint the boat. Ordinary oil-based porch and deck paint is the cheapest alternative. Linear polyurethanes are the most durable and the most expensive. Any pigmented paint is a better ultra-violet shield than a clear finish. When a paint finish is planned, all layout lines, pencil marks, dings, and scratches can be left in place during the construction process with no effect on the finished appearance of the boat. If you want a clear, natural wood or stained finish, you will have to plan for it from the beginning. Your first choices will relate to the materials used in the gluing and filleting operations described below. Filleting is the filling of inside corners with a thickened resin mixture to reinforce, and to round out inside corners before fiberglassing. All gluing and filleting operations involve the use of various thickening agents in addition to the resin that holds everything together. Many of these thickening agents are white or red in color, and they don't look very good under a clear finish. If you are planning a clear finish, use a mixture of fine sawdust, #406 colloidal silica, and #403 microfibers as thickening agents for all gluing and filleting operations. If you want to stain any parts of the boat, use an alcohol based stain, such as Watco Five Minute stain, rather than oil based stains. Epoxy will not adhere to wood that has been stained with an oil based stain! Do the staining right away, before any assembly process or contact with resin. If you are planning a stain finish, pre-stain the sawdust you plan to use for any filleting or puttying before you mix it with resin.

RE> paint

All fiberglass skins breath a little. Enclosed standing platforms people sometimes build into the front end of a fishing boat will eventually fill with water, not because they leak water but because they leak air, gasses. vapor, that has dissolved water vapor which eventually condenses. 

To apply a finish coat on top of any glass over plywood it's important to get the shop very warm, for at least an hour. Then back off on the heat a bit, so there is a warm but steady or even slightly falling temperature as you apply the finish. That minimizes the tendency for gas to bubble up out of the underlying panel. Problems like this are worse in cold wet weather. In dry areas like Montana we have less water vapor in the air and therefore less moisture lurking in the underlying plywood.