If you really have only a few surface scratches in your paint, a scuff sanding should be all that is necessary before a new coat of paint. Sanding down to the canvas is not just pointless -- sanding into the canvas could harm it. Similarly with interior and trim varnish -- a few scratches can be sanded down, and the whole surface scuff sanded, and then apply a good grade of marine varnish with ultraviolet inhibitors.
But if there is any chipping or peeling, or any deep gouges, some more preparation is needed.
No paint job is any better than its foundation – surface preparation is critical. Painting over peeling paint is pointless – the old paint will continue peeling, taking the good paint with it. But if the old paint is basically sound, and/or if you scrape/sand off the loose paint, a fresh coat of paint can make a canoe look better, even if the new paint job is not perfect, and even if the old paint is a bit cracked.
Repainting canoes is done all the time with all kinds of paints. Most use an oil based paint, and many use “marine” paints. Some use various other paints intended for exterior use – house paint, porch and deck paint, etc. Oil-based gloss paints are most commonly used. Water-based paints can work well, as can semi-gloss paints. They are easier to apply, and may be easier to touch up in the future – the chief disadvantage I have found with semi-gloss is that it is not so easy to keep clean, a particular problem with a light color.
Using premium marine paint over an old paint job is likely a waste of money. A good exterior paint – house paint, porch paint, Rustoleum enamel, or something similar – should do the job.
My experience suggests that, at a minimum, removing loose, flaking paint, and then brushing on a coat or two of paint, either water or oil based, will get you through a season or two of paddling for only a couple hours of minimal work, until you have the time and the inclination to spend the time on a proper restoration.
New paint will not keep old paint from flaking, so if you have flaking paint, it is important to remove all suspect paint, and then take steps to make the new paint stick. Sanding the flaking paint away may be sufficient, as long as what is under the old paint is compatible with the new paint to be applied. Spot putty may fill in very minor scratches and dings. In any case a light sanding over all is called for to help new paint adhere. After sanding, at a minimum I would thoroughly wash the surface (soap and water, or TSP) and rinse completely, and let the canoe dry completely before applying new paint. It may also pay to use a primer (Zinsser or Kilz).
More sanding, more spot putty, more primer will give you a somewhat better looking surface, with almost no improvement in function – at the cost of whatever extra work you wish to undertake – but you will not be able to make a silk purse out of a sow’s ear. It is very difficult to completely hide old cracked or crackled paint. To get that “silk purse” look, you will need to replace the canvas and then do a proper fill and paint job, when you have the time and inclination to do it right.
If the paint is tight, even if crackled, a coat or two of paint will prevent most, if not all, leaks and give you a serviceable canoe. But discretion being the better part of valor, it is wise to have a small roll of duct tape along if some of the old paint/filler under your newly-applied paint decides to flake off. Even without a duct tape repair, the resulting leak will likely be very slow and will likely not interfere with a day of paddling.
On our Old Town 50 pounder saw 5 seasons of use with old canvas, chipped filler, crackly paint, and a few unrepaired cracked ribs and planks, for just a few hours of necessary work -- sanding, spot priming, painting. (and a few more hours just messing around with unnecessary painting of decorative triangle designs) -- I didn't have the time to restore the canoe without losing a season of paddling. I used semi-gloss water based Benjamin Moore porch and deck paint for a paint job that served well for five years (with some easy touching up each season) before I beginning a full restoration.
Our Old Town Ideal, professionally restored, was painted with semi-gloss Benjamin Moore oil based porch and deck paint that has served well now for going on four seasons.
Here are some links to some discussions in these forums of painting over old cracked or chipped paint, when you want the paint to last only a season or three or five before re-canvasing:
http://forums.wcha.org/showthread.php?t=5790 see pp. 2-3 of this thread
http://forums.wcha.org/showthread.php?7769-Painting-over-existing-paint&p=41339#post41339
http://forums.wcha.org/showthread.p...t-Restoration-advice-please&p=32358#post32358
http://forums.wcha.org/showthread.php?7775-Temp-repair-to-bare-spot-on-canvas&p=41357#post41357
http://forums.wcha.org/showthread.php?7619-time-is-not-on-my-side!&p=40689#post40689
http://forums.wcha.org/showthread.php?8564-Smoothing-Canvas/page2 starting at post 12, on bondo spot putty
http://forums.wcha.org/showthread.php?6607-sanding-or-not&p=35286#post35286
[URL='http://forums.wcha.org/showth...cha.org/showthread.php?8906-Repaint-Tips[/url]
As for the tear in the canvas -- it is usually possible to slip a small piece of canvas or cotton cloth under the existing canvas, through the rip. Glue in place (Ambroid used to be the glue of choice, but it's no longer available; Titebond 2 or 3 or Duco cement should work). After the glue has set, smooth over the rip with Bondo spot putty or a bit of epoxy, lightly sand to smooth a bit, then a touch-up coat of paint over the disturbed area will finish up. It won't look perfect, but it should not be too noticeable -- especially if the rip is below the waterline. For a very short-term repair, there is always good old duct tape -- it will keep the water out, but won't do much for the appearance of your boat.
