by Mike Elliott, Kettle River Canoes
email: artisan@canoeshop.ca

A little research into traditional wood finishing methods shows that, for over a hundred years, there were three basic steps to finishing the interior of the canoe – Oil, Shellac, Varnish.  That said, I get a lot of e-mails and comments asking me about this.  It appears that much of the knowledge about finishing wood for outdoor use has been lost over the years or clouded by conflicting information.

Note: Oil, Shellac and Varnish are applied to bare wood.  If you are not stripping the old finish and simply want to add a coat of varnish to the existing interior finish, start by cleaning the varnished surface with TSP (tri-sodium phosphate) mixed in water.  Rinse the interior with clean water and let it dry.  Then, use fine steel wool to scratch the surface of the old varnish and make sure that all dust and debris is removed.  With the varnished wood properly prepared, it is ready for the application of new varnish as described below.

MYTH #1: Applying linseed oil to bare wood will hamper the adhesion of other finishes. Traditionally, linseed oil was the foundation of all interior finishing in canoes.  I must add that I am referring to “double boiled” linseed oil.  The name is rather misleading since the oil is not boiled but rather contains a variety of drying agents (japan drier is often used).  Raw linseed oil takes years to dry.  This is useful when you want a compound to remain flexible for years (i.e. Marine Bedding Compound such as Dolfinite).

A mixture of boiled linseed oil and turpentine – usually in a ratio of two parts oil to one part turpentine – has been the mainstay of wood preparation for exterior use for centuries.  The mixture soaks into the wood and keeps it supple and strong for decades.  It also prevents water from soaking into the wood thereby helping to prevent rot.  I apply a coat of the oil/turpentine mix to the entire canoe and let the oil dry for a couple of weeks (again, if you are leaving original varnish on the interior of the canoe, apply the oil/turpentine mixture to the hull exterior only).  The wood in old canoes is very dry and brittle, so lots of oil is required.  I apply a single coat of oil and let it dry for at least a week.

MYTH #2: Varnish will not stick to Shellac.  Shellac is fundamental to hard finishes on wood.  It creates a superb base for varnish and seals the wood in order for the varnish to ‘build’ properly.  It is easy to apply, dries in an hour or two, and polishes quickly with extra-fine steel wool.  Back in the days when woodworkers made their own varnish, shellac (as well as other gums and resins) was added to heated linseed oil to create the varnish.

Shellac is made from resins exuded by the female Lac beetle in India.  The resin is refined and dried in the form of flakes that range in colour from almost clear, through various shades of amber to dark orange (almost brown).  The shellac flakes are sold typically in one-pound bags which are then dissolved in denatured alcohol (ethanol mixed with a little methanol to prevent people from drinking it.  Methanol — also known as methyl hydrate can also be used on its own to dissolve the shellac flakes).

The concentration of shellac in the alcohol is referred to as the ‘cut’.  I normally buy pre-mixed shellac at the hardware store which is typically a ‘four-pound cut’ – four pounds of shellac flakes dissolved in one gallon of alcohol.  This is a rather thick mix.  Most woodworkers prefer a two-pound cut.  I dilute the pre-mixed shellac with lacquer thinner (a cocktail of volatile organic solvents usually including acetone, toluene, xylene and methyl ethyl keytone) in a 1:1 ratio.  Normally, shellac dissolved in alcohol is anhydrous and turns cloudy white when it comes in contact with water – not a good thing for canoes.  The addition of lacquer thinner prevents that from happening and gives a nice two-pound cut to work with.  In fact, shellac dissolved in lacquer thinner (primarily acetone) is often called lacquer.  If you are mixing your own shellac from flakes, dissolve them in lacquer thinner alone in order to create a coating that will not become cloudy when it contacts water.

Apply shellac with a natural bristle brush.  This stuff dries almost immediately, so application is fast and indelicate.  Apply lots of shellac to a small area to ensure full coverage with one brush stroke.  Shellac is more slopped on than painted on.  Once applied, do not go over an area again — one sloppy brush stroke and move over to the next small area.  It is important to maintain a wet edge as you move down the length of the canoe, so speed is the key. Allow the shellac to dry for a couple of hours at room temperature.  Then use extra-fine steel wool to polish the surface and create small scratches in the shellac.  Vacuum the canoe toemove any dust and debris and you are ready to apply varnish.

Myth #3: Varnish is difficult to apply.  Traditionally, varnish is made by dissolving gums or resins (such as shellac, rosin, mastic, amber, copal and damar) in heated oil (such as linseed oil or cotton-seed oil) and thinned with turpentine (distilled pine sap).  These days, most commercially manufactured varnishes contain petroleum-based alkyd polymer resins in oil thinned with mineral spirits (petroleum-based solvent).  A side note here is that some commercial manufacturers of varnish use the label Varathane® for a mixture of resins dissolved in linseed oil.  Meanwhile, a mixture of resins dissolved in cottonseed oil is known as Urethane®.

If varnish is used straight from the can, the high concentration of solids (alkyd resins) makes it almost impossible to apply without ending up with sags, drips, streaks or bubbles in the finish.  Consequently, conventional wisdom states that it is very difficult, verging on impossible, to achieve a smooth, even coat of varnish.  However, there is a simple solution.  Just thin the varnish about 12% with mineral spirits (paint thinner).  Some top-quality varnishes come with a higher concentration of solids and therefore require a little more thinning.  In any case, once thinned, the solvent allows the varnish to flow more easily which means that it will self-level to create a smooth surface.  The solvent also allows the varnish to dry faster thereby eliminating sags in the finish.

Before applying varnish, prepare the surface of the shellac base-coat or previous coat of varnish by scratching the surface with fine steel wool.  Too much rubbing will remove the previous coat, so quick and light is the key.  The scratches give the varnish something to hold onto.  Otherwise, the varnish will dry and then peel off.

Vacuum the surface thoroughly to remove dust and debris.  Then, go over the surface quickly with a tack-cloth to remove any remaining dust.

The interior of a wood-canvas canoe is irregular with lots of gaps and uneven surfaces.  Use a natural bristle brush to get the varnish into all the little nooks and crannies.  I use a 2” (55mm) brush.  It is a relatively major investment (currently costing about $48USD) and well worth it when called into service on a regular basis.  I used one brush on more than 100 canoes over a period of about eight years.  I finally had to retire it because the bristles had worn down to less than half their original length.

Set up your canoe in a well-lit space with good ventilation, away from direct sunlight.  Pour about two inches (5 cm) of thinned varnish into a clean, empty one gallon (4 litre) paint can.  Load the brush with varnish and rap the brush against the sides of the can to shake off excess varnish.  Apply the varnish quickly and vigorously making sure that it gets into all of the corners.  Work on a short section of the canoe.  Then, look at the surface from an angle with work lights set up at an opposite angle to reveal any areas that were missed.  Apply enough varnish to achieve full coverage while at the same spreading it thin enough to avoid drips or small pools.  Don’t worry about streaks or bubbles.  If the varnish is thinned properly, it will spread evenly and bubbles will disappear in a few minutes.  Once you have full coverage, ‘tip’ the surface by touching it lightly and quickly with the brush bristle tips.  It is best to tip the surface first across the grain of the wood and then with the grain.  However, it is difficult to tip in both directions in the canoe interior, so I usually just tip in one direction following the grain of the ribs.  The varnish is both applied and tipped very quickly.  Then, move over to the next section of the canoe.  Always maintain a ‘wet edge’ as you apply varnish to the full length of the canoe.  Work in small sections to make sure that the varnish in that section is still wet when varnish is applied to the next section.  That way, the entire surface will be smooth.  Once done, go away and leave the canoe in a well-ventilated, dust-free space for 48 hours.  I normally apply two coats of shellac and three coats of varnish.

Clean your natural bristle brush in three stages.  First, clean it with mineral spirits or turpentine.  Then, clean it with lacquer thinner.  Finally, clean the brush with a heavy duty cleaner such as Lestoil®.

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All of this (and much more) is described in my book – This Old Canoe: How To Restore Your Wood Canvas Canoe.
If you live in Canada, CLICK HERE to buy the book.
If you live in the USA, CLICK HERE to buy the book.
If you live in the UK, CLICK HERE to buy the book.
Si vous habitez en France, CLIQUEZ ICI acheter le livre.

If you have read the book, please post a review on Amazon and/or Goodreads and/or any other review site.

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by Mike Elliott, Kettle River Canoes
email: artisan@canoeshop.ca

repairs 06 SG

Without a doubt, the most horrible job in the restoration of a wood-canvas canoe is stripping the varnish from the interior.  It is messy, stinky, agonizing work that takes forever and cannot be rushed.  Truly, the only positive thing to be said about stripping varnish is that as long as you keep going, the job will end.

clean 03 CM

However, it is not always necessary to strip the old varnish.  If the interior varnish is in good shape – not peeling, cracked or gone altogether – you can simply clean the interior with TSP (tri-sodium phosphate) and rough up the surface of the varnish with fine steel wool.  After vacuuming the interior and removing any residual dust and débris with a tack cloth, you are ready to apply new varnish.  In my experience, if the varnish is stripped with chemicals, the canvas has to be replaced as well.  As a result, one big job leads to another.  That is why many people opt for simply cleaning the interior and applying new varnish to whatever is still there.

before 12 LCCa

If, as is often the case, the interior varnish is peeling away, breaking apart or gone completely, the varnish has to come off in order to rebuild the interior finish from the ground up.  Sometimes, the varnish is peeling so much that it comes off with a combination of a paint scraper, coarse steel wool and a lot of elbow grease.  I have tried sanders and “sandpaper stripping wheels” powered by a variable-speed drill, but soon gave them up when I saw that I was removing just as much wood as varnish.

strip 02 CL

When it comes right down to it, the best way to remove all of the old varnish (and still have the original ribs and planking left intact) is to apply chemical strippers. I strip the old varnish before removing the old canvas.  This way, the chemicals tend to stay inside the canoe.  They soak into the old canvas and lift the filler and paint from the canvas, so unless you are extremely careful with the chemicals, you cannot strip the interior varnish without then putting a new canvas on the canoe.

I have heard of some people using a pressure washer to remove the chemicals from the hull once they have done their job.  This would work well as long as the nozzle is wide enough to reduce the pressure to avoid ripping the planking apart.  One downside I see to removing the chemicals with a pressure washer is that the work is usually done outside, often in your backyard.  Consequently, all those nasty chemicals end up on the ground and (probably) in the water-table.  At the very least, you succeed in killing the grass in that corner of the backyard.

repairs 03 JK

When stripping varnish, the first step is to protect yourself from all those nasty chemicals.  The commercial products usually contain dichloromethane (commonly used as a propellant in aerosol cans) and methanol (wood alcohol).  Sometimes toluene (lacquer thinner) rounds out the mix.  Besides long sleeves, long pants and an apron or coveralls, be sure to wear gloves (heavy-duty latex/neoprene), a respirator and eye protection.  Have lots of water close at hand to wash off any stripper that contacts your skin.

repairs 03 SG

It is essential to maintain a wetted surface when using varnish strippers.  It evaporates quickly, so be sure to use lots of this stuff and do the canoe in small sections.  I usually divide the job into four quarters of the canoe.  Once the stripper has been poured onto a section of the canoe, use a sturdy scrub-brush (natural bristles) to spread the chemicals around and ensure that they get into every corner and let it work on the old varnish for about 20 minutes.  When it turns dark brown and becomes thick, you know it is working.

strip 02 EL

Use a scrub brush and a scraper to remove the stripper.

repairs 10 SG

Any stripper remaining in the canoe can be cleaned out with TSP mixed in a pail of water.  Use a scrub brush, a scraper and/or steel wool to ensure that remaining stripper is removed from all of the nooks and crannies.  Once the hull interior has dried, I go over the wood again with medium or fine steel wool to remove the last of the TSP and/or chemical stripper residue.  Then, vacuum the interior to remove the dust and steel wool fragments to finish the job.

students restoring canoes in penticton

This takes as long as it takes – no short cuts.  As with almost everything in life, if you don’t do a good job on the foundation work, it just creates problems later on.  As much as I want this job to be done as quickly as possible, there is no way to speed it up.  It takes time to do a thorough job.  In 2014, I coordinated the restoration of two 30′ C-15 Racing War Canoes (circa 1949) for the museum in Penticton, BC.  A crew of six people took five weeks and four times through the canoes with those nasty chemicals to remove all of the old varnish.  They were happy to see the end of that job.

mockup 02

All of this (and much more) is described in my book – This Old Canoe: How To Restore Your Wood Canvas Canoe.
If you live in Canada, CLICK HERE to buy the book.
If you live in the USA, CLICK HERE to buy the book.
If you live in the UK, CLICK HERE to buy the book.
Si vous habitez en France, CLIQUEZ ICI acheter le livre.