We’re about to start filleting our Chester Yawl at the Bow and Stern (page 29 of our instruction manual) but before I commit an egregious error, I want to confirm that the Epoxy Mix used to fill and create the fillet ACTUALLY covers the wires holding the Bow together and the Transom attached to the planks. There is no mention of removing the wires (and in fact, I think the pieces would come apart if I did) however, there is also no mention of whether to avoid the wires (for later removal) or bury them in the Epoxy mix.
So, do the wires get permanently buried or am I missing a step???
I expect that, whatever the answer, it also applies to the fillets used to secure the Frame pieces in place.
It’s your choice. The default in the manuals is to leave the wires in place and bury them in the fillets. Once the fillets set up, the external portions of the wires are clipped and removed.
Option 2 is to do the same, but rather than leaving the wire bits in the fillet, heat the wires by applying a soldering iron to the protruding bits until they’re hot enough to break the epoxy’s grip and pull them out with pliers.
Finally, option 3 is to tack the stitched pieces of wood together by applying dabs of epoxy/woodflour putty between the stitches and then removing the copper wires after the tacks have cured. Then it’s just a matter of filleting as normal. The picture shows a WD12 deck assembled this way, ready for filleting. If you look closely you can see the stitch holes between the tacks. Also, in some boatbuilding circles this method is incorrectly referred to as tack welding. Welding is where 2 pieces of material are liquefied so that they flow into each other and form a mechanical joint when they re-solidify. Try melting the wood and see where it gets you. This is actually chemical bonding, not welding.
Option 1 is the fastest and has the least steps. It’s also the heaviest and uses the most epoxy because of the need to bury the stitches.
Option 2 adds more work for hardly any return. The fillets are just as heavy and use just as much epoxy. Note that the wire may break during extraction. That individual stitch then reverts to option 1.
Option 3 takes the most time and prep but it uses the least epoxy, yields the most efficient fillets in terms of strength per weight and makes for the lightest boat. It also has an economic advantage in that you can get by with less epoxy, AKA liquid gold, and you have all the copper stitches available for reclamation (currently almost $6/lb).
Any of these options will work and yield a fine boat that you will have lots of fun with, so pick whichever you’re the most comfortable doing.
CA Glue isn’t cheap but I can see that working as a temporary joint. Is it strong enough to hold during assembly? I’m a beginner at this (although have done woodworking for years) and it seems as if there is a tremendous amount on tension on the copper wires and the joints would fail as soon as there is any movement at all.
Option 4, which I much prefer, is to do the tack gluing with cyanoacrylate (CA) super glue, then pull the wires, then filet. The CA is cheap, light, and sets up very quickly. You can even use the accelerator spray (which I think is simply acetone) for nearly instant set-up of the glue. The CA joint is NOT very strong when the wires are pulled, prior to getting the epoxy filet done, so it is possible to hear a CA joint pop or crack if for some reason you were to put a lot of stess on the boat by trying to roll it over or tighten up additional panels with stitches. This isn’t a big deal - just avoid doing that when the only thing holding the joints is the CA glue. You also might find that you want to use epoxy to tack some very high-stress joints, or joints with large gaps, prior to pulling the stitch wires. I do recommend always pulling the stitch wires prior to filet, no matter what tack method you use.
Using CA glue for most tacks is a huge time saver - both because there is no prep time for the glue, and because it goes into the joint so accurately and with no mess. This subsequently allows you to filet without having to filet over any wires, or filet over any epoxy tack bumps, resulting in smaller, more uniform filets. Even if you decide to use epoxy tacks, get in the habit of making the tacks as small and infrequent as possible - in many places you don’t need to tack between every stitch.
Also, no matter what method you choose to use, read up on filet technique. By using a frosting piping bag (highly recommended in most cases), making a neat filet, choosing a smoothing tool of the proper radius based on the size and joining angle of the joint, using a scraper to clean up any random drips, sometimes using blue tape on the outside of the filet (which is pulled immediately after the filet is laid in), and using the rubber-glove-alcohol-finger technique to smooth the filet (a VERY IMPORTANT skill to develop) while it is in a semi-plastic state (30 minutes to two hours after laying in the filet, temperrature/epoxy set speed dependent), you can lay in filets that need no, or next to no sanding. Achieveing no-sand filets is a huge time saver and makes your boat look better.
Finally, if you use about 50 percent wood flour and 50 percent cellofill to thicken the epoxy for your filets you’ll find you can nearly match the color of the okume plywood. This prevents the dark “stripes” created by 100 percent wood flour filets in areas, so is worth doing in areas with a visible, bright finish. Be advised cellofill in epoxy is always a little more difficult to sand than wood flour, so again, neatness counts.
Note the filet at the right side of the dash on my Rhode Runner. You have to look closely to see it . Color matched, laid in neatly, smoothed with the finger technique, and next to no susequent sanding.
I checked the CLC website. They sell medium viscosity, so that is what I used. I think two of the 2 oz. bottles will be enough. If not, getting more is a pretty quick pursuit either through CLC or the local builder supply/hardware store. If too much, of course the stuff is always useful around the house, but shelf life is limited once opened. I’d get one of the spritz bottles of accelerator, too. I never used the de-bonder on the boat, but did find it useful to help clean up fingers. I don’t know why I can’t keep gloves on all the time, and I always find myself sticking my bare fingers where they don’t belong, no matter whether I’m painting, caulking, varnishing or gluing a boat or anything else around the house. The stuff also works well to seal up stitch holes once wires are removed - preventing drip-thru of epoxy or varnish when you are coating pieces.
Concerning CA glue and alcohol fillet smoothing, first let me say that I know that there are at least hundreds, if not thousands of builders out there who have successfully used those techniques in their builds, so they definitely work.
That said, I still can’t bring myself to use them because it’s introducing a possible contaminant into the joint. I know that the evidence shows that they all work together - epoxy, CA glues and denatured alcohol - but my concern is that’s for the case of past formulations. These days every manufacturer seems to be constantly hunting for ways to save a dime here and a nickel there. The supply chain is also extremely unstable since COVID 19. Toss in the scrambling to avoid tariffs on raw materials, as well as changing environmental regulations around the world and you really can’t be certain of what exactly is in your epoxy, CA glue and alcohol and if they will still play nice the way they did last week.
One thing that is absolutely certain is that the epoxy in a bottle is compatible with itself. That’s why I use epoxy to tack between stitches and why I smooth fillets with unthickened epoxy. Jeff’s point about no-sand fillets is spot on and unthickened epoxy works just as well as denatured alcohol for that without a risk of contaminating the joint.
(BTW, epoxy tack bumps can be avoided with good technique. By using thin smears instead of miniature fillets for tacking, the final fillets can be very thin, indeed, and not protrude above the wood. In the picture below you can see that the final fillets fit entirely between the stitch holes, even though they were applied over epoxy tacks.)
Anyway, that’s why I prefer not to use foreign substances in my fillets. I know they’ve worked beautifully for others, but I don’t trust trying to integrate 3 different chemicals made by 3 different manufacturers in these uncertain times.
I am also a fan of using CA glue (also known as super glue) during stitch and glue builds. I would not worry about chemical contamination because this is the prescribed method in the CLC build manuals for S&G Petrel and Petrel Play kayaks. You can buy CA and accelerant directly from CLC but it is re-labeled product made by Bob Smith Industries, which is available at most hobby stores or on Amazon. Picture below is the deck of my S&G Petrel Play prior to filets. The copper wires were removed after CA was dots were applied about every inch.
. Color matched, laid in neatly, smoothed with the finger technique, and next to no susequent sanding.
