Tech Tip Tuesday

I would guess that this is one of my more overdue posts.

It is about the steps between the finishing process and the 'glassing process. After the canoe is stripped, outer stems (if you have them...) are installed and shaped, and any fasteners used to hold strips in place have been removed (if you didn't go staple-less..) you need to fair the hull. At this point, the hull has facets made up of the individual strips.

You want a nice, smooth, fair hull - by fair, I mean "canoe shaped" without dips or lumps. Fairing is accomplished with planes, spokeshaves and longboards. I've talked about fairing and longboarding before so I will not go into detail here.

After you've faired, take a cloth with warm water and dampen the hull slightly - this will make any residual glue spots show up more clearly. Circle these areas with a pencil (lightly - so as not to make dents!) so when they dry you will know where to sand to remove the glue. It will show up as light spots when you fiberglass the hull.

In the process of building a cedar strip canoe, most beginning builders will have some small areas where there are gaps, checks or holes in your boat. First, I should explain that they're not a problem for how waterproof the canoe will be - they're mostly cosmetic, but can cause some problems during the fiber-glassing process. The major problems are bubbles caused by air escaping from the gaps and epoxy running between the hull and the forms - either bonding the hull to the forms or the forms to the strongback. This can also lead to "starved" spots in the fiberglass cloth.

To deal with any of these areas, we make what Nick Shade of Guillemot Kayaks refers to as "Dookie Shmutz". This is a mixture of epoxy that has wood flour added to it to color the epoxy and some fumed silica to make a non-sagging mixture. Wood flour is simply what it sounds like - fine wood dust - you can get a good color match by saving any sanding dust from the fairing process. By non-sagging, I mean that it doesn't run. The mixture should be about the consistency of peanut butter.

Some people have recommended mixing white glue with the wood flour to make a paste filler, using wood putty (i.e. "plastic wood"), auto body fillers or even some of the pre-thickened epoxies such as System Three's Quick Fair or Gel Magic. First, I can't recommend wood putty or auto-body fillers as they are brittle. I don't recommend using wood glue mixed with wood flour for two reasons - the epoxy doesn't bond to the glue and cosmetically it's not very good-looking on a bright-finished canoe. If you are not going to have a bright finished canoe, (i.e. a painted canoe) you could use the other epoxy-based fillers.

So, if you are going to have a nice looking bright finished boat, you'll mix yourself up some Dookie Shmutz. We usually use poly squeegees to apply the filler to the cracks. The best way to think of it like spackle for holes in the wall, but for your boat - you want it in the cracks, but not all over the wall. Dookie Shmutz that gets on the lighter colored wood will show if you don't remove it by sanding later. This material is very, very hard when cured, so you don't want to get too much excess on the hull. It's not out of line to use some masking tape around the gaps to help keep as much of the filler off the hull as you can.

This is what the bow of the Prospector Ranger looks like after some filler has been applied:




In the bottom picture, you can see that some of the material near the stem has been sanded away. In the next image, you can see some dark lines that are showing between the strips and all the excess has been removed from the wood.


While the filler looks dark now, once the hull is saturated with epoxy and 'glassed, it will darken. Over time, the cedar will mellow and darken, getting closer in color to the the filler. Still, you must keep in mind that both the Dookie Shmutz and any areas of the cedar that have been damaged by staples, nails or any other mechanical damage, will be slightly darker because the fibers have been damaged and simply are darker in color.

Building a Cedar and Canvas Canoe : Friday

Friday was a very big day in terms of work. The major woodwork for the hulls was complete. This is what we started the day with:

The line of blue tape was holding a chip that we'd glued back into the rib. It had split out when we were doing some clenching the day before.

The hull was grossly fair and straight, but required some minor fairing to get rid of some lumps and puckers in the bow and stern quarters at the turn of the bilge. This was accomplished with a good size disk grinder and a smaller palm sander to follow up. At this point, the ends of the planking at the stems was made flush and tapered a bit to make the ends a bit finer.



After this operation was complete, the outside of the hull was given a light coating of boiled linseed oil and turpentine to help to make this part of the hull a bit waterproof. It is also used to help inhibit the growth of mold and mildew on the planking. We thought the hull looked nice at this point.

After the hull was prepared, we folded a length of canvas in half lengthwise and used large wooden clamps to hold the ends, one end of which was attached to a large post wedged between the floor and the top beam of the canvas stretching assembly. The other end was attached to a fixture that was in the window opening and had a come-along which is used to tension the canvas. The inside of the boat is protected with cardboard and props wedged between the ceiling and the boat are used to push the boat down into the canvas.



Here's Jerry checking on the props used to force the boat down. One of the clamps is in the foreground on the right. This method was a departure for me. I'm used to stretching canvas outside between two trees and using bags of sand and other heavy objects to push the boat into the canvas. There are many ways to skin that cat.

Big "clothespins" are used at both ends to bring the canvas together at the stems. The canvas is then stretched up using special pliers commonly used for other tasks (Artist's canvas stretching pliers and welding Vise-Grips) The canvas is then tacked into the ribs and inwale just below the edge of the planking. Here is a picture of that task (Not our boat, but still the same class.)



You can just see the desired puckers that appear in the canvas if you've got good tension.

After all the tacking at the gunnel line is complete, the canvas was cut and the boat taken down. Here's our boat on sawhorses with the "clothespins" still in place.



At this point, the canvas hasn't been wrapped around the stems yet. A layer of bedding compound is put on the stems and the canvas is cut from the point at which it makes good contact with the stem and out away from the boat along the centerline. The first side is then drawn off across the stem and tacked every 3/4" or so with short tacks. This gets rid of any wrinkles along the sides of the boat in the front quarters. The leftover canvas is trimmed up against the stem. Another layer of bedding compound is applied and the process repeated for the other side. What you are left with looks like this:



You can just see a bit of bedding compound at the edge of the cut.

Before you can fill the canvas (No, I'm not giving away the formula for the filler! Old Timers guarded these trade secrets carefully...) you have to get rid of the nap (AKA : fuzz) on the canvas. this is done like this:



Yes, that is a propane torch we're running over the surface of the canvas on a nearly finished canoe. You can see the burn marks from previous passes. You need to be very careful and work fairly quickly avoiding any hanging threads or frayed edges.

I didn't get any pictures of applying the filler, but suffice it to say, it is mostly like painting the boat with rollers. If you look at my post from Saturday you can see the smooth slate gray finish. This is achieved by taking a canvas "mitten" and rubbing the surface of the hull after the filler is applied with the roller to smooth the surface and "kill" the weave of the cloth. It's not difficult, but takes quite a bit of energy. I also scorch the surface of my mittens to avoid getting lots of fuzz in the finish.

The other important thing to note is that we didn't paint or varnish the hull because the filler needs to cure. The filler contains oils that need to polymerize over a long period of time (4-6 weeks or even longer, depending on conditions) to be properly cured. After the hull is cured, 5 coats of varnish will be applied to the interior and 5 coats of good enamel paint applied to the exterior. Stem bands and (if desired) a keel are installed after this finishing.