On Sunday night's post about stretching canvas, I was a bit light on detail. There are, however some excellent resources for detail.
Two of them are books. One is by Jerry Stelmok and Rollin Thurlow and is called The Wood and Canvas Canoe. Another book is by Jerry Stelmok and is entitled, Building the Maine Guide Canoe. Both titles are widely available from places like the WoodenBoat Store and the Wooden Canoe Heritage Association's (WCHA) online store.
In these books are some places to find materials that you will need for the job. In particular, the canvas, brass tacks, stem band and filler. There is also an excellent list of suppliers over at the WCHA. I would be remiss in not mentioning that WoodenBoat offers an excellent school where you can take classes (see my earlier posts on the topic) and many builders offer both building and restoration instruction at their shops for a fee - very often all you need to do is ask.
Showing posts with label stretching canvas. Show all posts
Showing posts with label stretching canvas. Show all posts
Tuesday, December 16, 2008
Thursday, December 11, 2008
Stretching Canvas
One of the things that I've found in talking about cedar and canvas canoes with people is their absolute terror at the thought of replacing canvas on a canoe. I don't know why that is, but it seems to be one of those psychological roadblocks that keeps people from restoring and repairing their canoes. It's not that difficult. The big downside is waiting for the filler to cure once the actual canvas work is done.
Before you start, you need to take off the old canvas. This usually involves removing the outwales and removing the tacks hidden beneath that held the canvas in place. You may also have a keel and brass stem-bands to remove. Typically, all of the fasteners are found along the gunwales and from stem to stern at the centerline of the canoe.
Once the canvas is removed, you will want to inspect the woodwork to see if there is rot, cracked planking or ribs, loose tacks or any varnish work that it needs. If there is such damage, now is the time to repair it.
Once any necessary repairs have been made, make sure the outside is smooth and fair and give it a light sanding and a light coat of linseed oil and turpentine. This helps to waterproof and preserve the wood. When done, the boat looks like this:
You should also have your materials collected. You'll need a few specialty items and a few tools.
After cutting the appropriate length of canvas, fold it in half the log way with the opening at the top and clamp both ends with the keyed wooden blocks. The key keeps the canvas from slipping out under tension. The blocks are clamped together using two or three C-clamps. When this is done, pull up the tension on the canvas to make sure there aren't any wrinkles.
Let the tension off and put the boat in the envelope of canvas. Think of it like a hammock for your boat. Be sure it is well seated in the canvas. Pull up on the tension again, but not so much that you rip the canvas or it slips from the clamps. You will then need to either weight the canoe with bags of something heavy or if you have a ceiling overhead, you can use some wood to prop the boat down from the ceiling. The best way is to protect the inside of the boat with cardboard, put a 2x6 in the bottom of the boat and use another piece of lumber to wedge between the 2x6 and the ceiling joist. Install the canvas "clothespins" at either end as close to the stems to hold the canvas near the hull at the ends.
The longer tacks are then put in. There are two at each rib, just below the top edge of the planking. Usually a scrap of wood is used to protect the inwale. You then grab the canvas with the canvas-stretching pliers and rock the handles into the hull on the block of wood. (In the picture below, the pliers are upside down - see the rounded top?) Placing tacks is done by Braille - you need to feel for the rib location and the top of the planking - sometimes you can see the rib through the canvas. You'll want to be about 1/4" down and 1/4" in from the edges so you don't split planking and ribs. If you get the tension correct, there will be little puckers above the tacks. Make sure any wrinkles in the canvas are being moved from the center of the hull towards the stems. Tacking the canvas is most easily accomplished with two people.
Alternate sides to keep the tension on the canvas even. If there are wrinkles, pull up on the canvas a bit harder. As you get close to the ends, you will also find that you need to trim the canvas near the gunwale so that the pliers can "bite" the canvas for a good grip as there will be too much fabric. You will also find you have to pull the canvas towards the stem to get rid of the wrinkles. When you get all of the tacks put in at the gunwale line, you need to make a choice. You can:
A) Simply let down the tension and cut the canvas (vertically) about a foot beyond the end of the stem. The excess canvas helps you to pull the fabric around the stem to finish this area.
OR
B) Roll a scrap of canvas to be a small "sausage" about 5 layers thick an inch wide and about 4' long (depends on stem length) and staple parallel to the stem through the "sausage" and the canvas into the planking and stem on both sides of both stems from deck to keel. Then cut down the hull as above. You will need to work any wrinkles out as you staple this in place.
The advantage of B is that as you're tacking the stems in place, there is not tension. This is an advantage if you are working alone.
Put the canoe upside down on a pair of saw horses and remove the clamps.
Before you tack the stem slit the canvas down the middle of the envelope. You start this cut at the keel where the fabric would overlap. Put one tack in the stem just above the slit. Then, apply a thin and even layer of bedding compound over the stem and pull the canvas off "normal" to the stem so you get no wrinkles. Starting at the keel and heading towards the deck tack every 3/4" or so. It should look like the the picture below. The wrinkle to the right of the stem shouldn't be there...
Trim the excess canvas close to the stem on the that hasn't been tacked. Apply bedding compund again and repeat in the other direction. Trim the excess canvas again and repeat for the other end of the boat:
The next step is to apply the filler to the canvas. The filler is a tough, abrasion-resistant coating that fills the weave of the cloth and effectively waterproofs the boat. There are leaded and unleaded fillers. I personally prefer the leaded filler for the anti-microbial properties of the white lead. If you avoid contact with the lead, you should do OK. I think it's nice to label the inside of the boat somehow to let a future restorer know that they are dealing with lead... The leaded and unleade filler apply almost the same way, but the leaded tends to inhibit mildew in the canvas for many, many years.
It's applied by brushing on with a heavy brush and then rubbing in with a canvas mitt. (Wear latex or nitrile gloves underneath if it's leaded filler!) It may take several coats. You'll know when to rub with the glove when it rubs smoothly and leaves you with a slate-like finish.
Whe the filler is applied, it will take a few months (yes months - 2-3!) for the filler to cure or "polymerize". When cured, you can sand (wear a mask!) and apply primer and paint - usually a porch and floor enamel and re-install keel, stem band and outwales.
Happy Paddling!
Before you start, you need to take off the old canvas. This usually involves removing the outwales and removing the tacks hidden beneath that held the canvas in place. You may also have a keel and brass stem-bands to remove. Typically, all of the fasteners are found along the gunwales and from stem to stern at the centerline of the canoe.
Once the canvas is removed, you will want to inspect the woodwork to see if there is rot, cracked planking or ribs, loose tacks or any varnish work that it needs. If there is such damage, now is the time to repair it.
Once any necessary repairs have been made, make sure the outside is smooth and fair and give it a light sanding and a light coat of linseed oil and turpentine. This helps to waterproof and preserve the wood. When done, the boat looks like this:
You should also have your materials collected. You'll need a few specialty items and a few tools.
- Canvas - It should be an appropriate weight for the boat your building - typically #8 -heavy, #10 - Typical or #12 - lightweight and longer than the boat by about a yard or two.
- Brass Tacks - AKA Canoe tacks - in two lengths - 7/8" to 11/16" for the at the ribs and 5/16" or 3/8" for the stems.
- Bedding Compound - a peanut butter consistancy material for the stem ends.
- Filler - a thick paint mixed with or without white lead for "killing the weave" on the canvas. More on this later.
- Brass Stem Band and Screws
- Cardboard
- Prop sticks or weights (sandbags, garden fertilizer, etc.)
- Winch - AKA "come-along"
- Chain and hooks
- C-Clamps
- ~3' Blocks with "key" for clamping canvas as stretched and eye bolts to pull canvas. - one set for each end of the canvas.
- Canvas "clothespin" - a piece of hardwood with a wide kerf cut up the middle (lengthwise) and a bolt to prevent it from splitting at the closed end of the kerf.
- Canvas Stretching Pliers
- Small Hammer
- Razor Knife
- Screwdriver
After cutting the appropriate length of canvas, fold it in half the log way with the opening at the top and clamp both ends with the keyed wooden blocks. The key keeps the canvas from slipping out under tension. The blocks are clamped together using two or three C-clamps. When this is done, pull up the tension on the canvas to make sure there aren't any wrinkles.
Let the tension off and put the boat in the envelope of canvas. Think of it like a hammock for your boat. Be sure it is well seated in the canvas. Pull up on the tension again, but not so much that you rip the canvas or it slips from the clamps. You will then need to either weight the canoe with bags of something heavy or if you have a ceiling overhead, you can use some wood to prop the boat down from the ceiling. The best way is to protect the inside of the boat with cardboard, put a 2x6 in the bottom of the boat and use another piece of lumber to wedge between the 2x6 and the ceiling joist. Install the canvas "clothespins" at either end as close to the stems to hold the canvas near the hull at the ends.
The longer tacks are then put in. There are two at each rib, just below the top edge of the planking. Usually a scrap of wood is used to protect the inwale. You then grab the canvas with the canvas-stretching pliers and rock the handles into the hull on the block of wood. (In the picture below, the pliers are upside down - see the rounded top?) Placing tacks is done by Braille - you need to feel for the rib location and the top of the planking - sometimes you can see the rib through the canvas. You'll want to be about 1/4" down and 1/4" in from the edges so you don't split planking and ribs. If you get the tension correct, there will be little puckers above the tacks. Make sure any wrinkles in the canvas are being moved from the center of the hull towards the stems. Tacking the canvas is most easily accomplished with two people.
Alternate sides to keep the tension on the canvas even. If there are wrinkles, pull up on the canvas a bit harder. As you get close to the ends, you will also find that you need to trim the canvas near the gunwale so that the pliers can "bite" the canvas for a good grip as there will be too much fabric. You will also find you have to pull the canvas towards the stem to get rid of the wrinkles. When you get all of the tacks put in at the gunwale line, you need to make a choice. You can:
A) Simply let down the tension and cut the canvas (vertically) about a foot beyond the end of the stem. The excess canvas helps you to pull the fabric around the stem to finish this area.
OR
B) Roll a scrap of canvas to be a small "sausage" about 5 layers thick an inch wide and about 4' long (depends on stem length) and staple parallel to the stem through the "sausage" and the canvas into the planking and stem on both sides of both stems from deck to keel. Then cut down the hull as above. You will need to work any wrinkles out as you staple this in place.
The advantage of B is that as you're tacking the stems in place, there is not tension. This is an advantage if you are working alone.
Put the canoe upside down on a pair of saw horses and remove the clamps.
Before you tack the stem slit the canvas down the middle of the envelope. You start this cut at the keel where the fabric would overlap. Put one tack in the stem just above the slit. Then, apply a thin and even layer of bedding compound over the stem and pull the canvas off "normal" to the stem so you get no wrinkles. Starting at the keel and heading towards the deck tack every 3/4" or so. It should look like the the picture below. The wrinkle to the right of the stem shouldn't be there...
Trim the excess canvas close to the stem on the that hasn't been tacked. Apply bedding compund again and repeat in the other direction. Trim the excess canvas again and repeat for the other end of the boat:
The next step is to apply the filler to the canvas. The filler is a tough, abrasion-resistant coating that fills the weave of the cloth and effectively waterproofs the boat. There are leaded and unleaded fillers. I personally prefer the leaded filler for the anti-microbial properties of the white lead. If you avoid contact with the lead, you should do OK. I think it's nice to label the inside of the boat somehow to let a future restorer know that they are dealing with lead... The leaded and unleade filler apply almost the same way, but the leaded tends to inhibit mildew in the canvas for many, many years.
It's applied by brushing on with a heavy brush and then rubbing in with a canvas mitt. (Wear latex or nitrile gloves underneath if it's leaded filler!) It may take several coats. You'll know when to rub with the glove when it rubs smoothly and leaves you with a slate-like finish.
Whe the filler is applied, it will take a few months (yes months - 2-3!) for the filler to cure or "polymerize". When cured, you can sand (wear a mask!) and apply primer and paint - usually a porch and floor enamel and re-install keel, stem band and outwales.
Happy Paddling!
Wednesday, August 27, 2008
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.
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.
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