Kirby's Canvas Filler for Wooden Canoes is a traditional oil-based filler It contains alkyd oil and silica-based fillers. Cures to a durable finish.
How much is needed?: One gallon of filler will do a 16-foot canoe covered with #10 canvas. Order an additional quart for a 17 or 18-foot canoe.
Filling canvas on a wood/canvas canoe:
Instructions by Bill Clements, Boat Builder and original maker of Kirby’s Wooden Canoe Canvas Filler
Use in a well-ventilated area. Avoid skin contact by wearing gloves.
This filler contains a high percentage of silica and calcium carbonate that will quickly settle to the bottom of the can. The filler must be stirred well before use and throughout the operation.
With the canoe upside down on sawhorses, start at one end working from the horizontal centerline (keel line) down to the gunwale. Apply the filler with a 9” foam paint roller in 12” to 18” wide sections. Roll on the filler until the canvas retains a wet look. Then, using a canvas mitt, rub it in using a circular motion until the mitt starts to drag. Roll filler onto the next 12” to 18” section in the same manner as above and also roll a light coat over the previous section. Rub this second section with the same circular motion as before. Go back to the first section and rub it with lengthwise strokes parallel to the keel. Still on the first section, using a piece of scrap canvas, about 8” or 9” square, polish the area much like you would use sandpaper on wood. Carefully examine the surface for any areas for thin spots where there is fabric showing or pits. Add a small amount of filler to any of these areas and rub it in with the scrap canvas. For the final step, using only your gloved hand, do one more rub-down. If your glove sticks to the surface, it means the filler has not set up enough yet so give it a few more minutes. Proceed in this fashion, section by section, until you have completely filled one side. Follow the same steps on the other side. The reason for working back and forth between two sections is that the filler needs a few minutes to “set up” before it can be properly finished.
The idea is to just fill the weave without getting a heavy surface buildup. If you find that the filler is setting up too fast, which can occur under warm or dry conditions, thin the filler with a 50/50 mixture of mineral spirits and linseed oil. If you do not have any linseed oil, use just mineral spirits, only not as much. Use no more than ½ pint of this mix per gallon of filler. As you work your way around the canoe, look closely at the overlap areas for excessive build-up. You can use pieces of canvas scrap to blend in these overlaps.
Use as much time as it takes to get the surface smooth. Cured filler is very difficult to sand. The filling operation should take about 3 to 4 hours and must be completed in one operation. Avoid taking breaks of more than half an hour.
The filled canoe will need 6 weeks to cure. Do not try to rush the curing process by placing the canoe in the sun as this can cause the filler to crack. I speak from experience. Once cured, the filler can be lightly wet or dry sanded with 120 or 220 sandpaper. Most paints are compatible with the filler.