The time to strip your canoe of old varnish is before you recanvas. The chemical strippers necessary for the job will seep between the planking and affect the filler and paint on the canvas if it is done either with existing canvas on the canoe or after the canoe has been recarnvassed. If the varnish is old and in poor shape, but you aren’t planning on recanvassing, then the best you can do is to sand and scrape thoroughly brefore varnishing.
Stripping old varnish from the inside of a canoe is a messy job best done outdoors. I use a chemical stripper called F400 that I get from Four-Most Chemical in Streetsville, ON, Canada ( 905-826-2022). It is a liquid stripper containing methylene chloride and who knows what other deadly chemicals. I find the liquid to work better than the semi-paste. Depending on how heavy your varnish is, it will take at least two gallons. It works best at temperatures between 15 -20°c, (60 and 70°f), and on an overcast day or in the shade. A hot sunny day makes it very hard to keep the varnish wet with stripper and you will either have a poor result or use much more stripper than is usual. I finish the process with pressure washing the inside and this stripper is compatible with this method. If you use a different stripper it will probably be a good idea to do some tests first. It could be that because this is not a semipaste, it is more compatible with the water wash.
I like to cover up with coveralls, hat, goggles, and latex gloves under a pair of heavy rubber gloves. Be aware that the stripper will eat plastic so watch out for your glasses. I don’t believe that a charcoal filter mask actually keeps out the methylene chloride - I don’t use mine, somehow thinking that working outdoors will take care of the fumes!?!
Set the canoe up on sawhorses in the shade. I haven’t found the stripper to affect grass but then I choose a spot out of the way in the long unmown area behind the shop. I find it best to leave on the old canvas as it catches and keeps the stripper in the canoe where you want it to do its job.
Pour the stripper into a 19 oz can and slop it on with a pure bristle brush. Be generous and work quickly down the length of the canoe. It helps here to have a friend to share the job. I go right back again and slop on a second coat and then cover the whole canoe with a sheet of plastic held in place with spring clamps. I leave it for about a half hour and then go back, peeling back the plastic part way down the canoe and applying more stripper. The trick is to keep the inside pretty wet with the stripper - if it dries right out then it just re-adheres and you are starting from scratch again. This time around I apply the stripper with an old plastic kitchen scrubbie brush and gently work the now loosened varnish down to the floor of the canoe. You can reuse the liquid that puddles in the bottom even though it looks all dark and vile - as long as it is wet it will still strip. I gradually work my way down the canoe, lifting back plastic and replacing it as I go. By this time the varnish will be pretty much off and be a gucky mess in the bottom.
I take an old spoon and plastic squeegee now and pick up as best I can the majority of goop from the bottom and place it in an old paint can. Finally I go over the whole canoe again with paint brush and new stripper and make sure every part is moistened. Now is the time to blast it out with a pressure washer. I set the canoe up on one sawhorse with the other end on the ground, tipped on its side and pressure wash the inside. It takes patience but if you go rib by plank by rib you will find that any varnish left on will have been loosened by the stripper and will come off with the water stream. When it looks good, I then remove the canvas from the outside and spray off the exterior taking care to work along the plank lines. Now a final spray of the interior and the messy job is over.
The canoe will be soaked at this point and will need several days to a week to dry out sufficiently before work can begin. Before any varnishing you will want to replace all broken ribs and planking. I have found that my stripper needs no rinsing other than the water before starting the varnishing phase. You will have to check into the stripper that you use, as you might find it necessary to rinse with alcohol (methyl alcohol) or other thinners first.
Before varnishing I thoroughly sand the interior with 120 grit on the ribs and either 3M purple pad or 220 on the planking. It is next to impossible to sand with the grain on the planking so I go up and down, across the grain but do so very carefully so as to leave very little scratching. If the stripping job has been really good sometimes I won’t touch the planking.
Once all the woodwork is done, now is the time to stain any new wood to match the old. And it is often a good idea to give the interior a coat of boiled linseed oil and thinner mixed 2:1 to give back some flexibility to old brittle wood. I like to let it dry now for 2 or 3 days before proceding with the varnishing.
The first varnish coat should be cut 50% with mineral spirits to aid in its absorption into the wood. After 24 hours I knock off the raised grain of the ribs with 180, and again usually don’t touch the planking. Coat 2 is usually cut by 20 to 25 %. This is followed by sanding the ribs with 220 and the planking with the purple pad. Coat 3 is cut by 5%. I usually find that 4 coats is enough on an interior so the sanding now is 220 on ribs and 320 on planking. This is the time to be diligent and sand out any sags, runs or dust before the final coat of varnish.
I use Epifanes Varnish and find it builds up quickly and has incredible gloss. Petite or Woolsey Hi Build is also good varnish and a little thinner and easier to apply. Its gloss doesn’t seem quite as good and it is a little more yellowing. I have found it helpful to hang a light bulb down into the middle of the canoe, and up off the floor of the canoe by and inch or two - it set up an air current that moves the solvents out of the inside of the canoe and helps the varnish to kick.
It is usually a good idea to do all varnish coats on the interior before canvassing and filling the canoe. Occasionally, depending on the filler used, varnish after recanvassing can affect the canvas where it seeps through the planking creating unsightly blemishes on the exterior painted surface.
