Painting : How to Paint Boat - Exterior Wood

Types of wood finishes:
Paint.
Varnish (paint without pigments).
Oil (Cetol, Armada ?).
Acrylic urethanes (Bristol Finish, Honey Teak). Oils and varnish, from "Coating With Oil" article by Bob Flexner in Workbench magazine Feb/Mar 1992:

These all are marketed as "oils":
Straight oils (tung or raw linseed or boiled linseed).These are "curing" oils; they change to a solid in air.They are fairly soft after curing; you can dig a fingernail into them.Many coats to get a satin sheen.

Polymerized (heat-bodied) oils.Builds a hard, glossy film. Expensive and rare. E.g. gunstock finish.
Wiping varnishes: varnish thinned with mineral spirits.Often sold as "oil" or "Somebody's Tung Oil" or "Somebody's Tung Oil Varnish".Hard when cured. Cures glossy.
Oil-varnish blends: a mixture of straight oil and varnish.Often sold as "Somebody's Oil".Soft when cured; wrinkles if cured thick.Satin sheen after one or two coats.Varnish is made by cooking a curing oil with a hard resin (usually synthetic alkyd, phenolic or polyurethane) to make a new substance that cures fast to a hard, glossy film.

The protection any finish film gives depends largely on its thickness. The first coat is the only one that penetrates into the wood. Depth of penetration is controlled entirely by curing time, not by rubbing; rubbing actually makes it cure faster. Varnishing wood:

Types of varnish:
Alkyd resin: very pale, clear, doesn't yellow, but not lustrous.
Phenolic resin: deep luster, darkens and yellows on drying, excellent durability.
Polyurethane resin: paler than phenolic, ages better, extremely hard and durable, can be applied in very hot conditions. Want varnish that contains UV protection.Ways to strip varnish from wood: sanding, chemicals, heat gun


From Jeff M on Cruising World message board:
... Sanding to remove varnish on large areas is not recommended; use chemicals or a heat gun. ... The heat gun is a great idea, especially for long flat runs. I caution against waiting for the varnish to bubble though. Not very long after bubbling is burning, and if it is your first time, you have a large chance of burning the wood. (If you think your moisture-blackened mahogany looks bad now, try charring it.)

I recommend holding the heat gun in one hand, and the scraper in the other. Warm the varnish over a 1 foot area and keep test scraping every 15 seconds. You will feel the varnish soften, long before it bubbles. As it gets warm enough, it will peel off easily with a soft rubbery texture. The older the varnish, the more heat rquired. Keep the heat gun moving. Don't wait for all of the surface to bubble. Just a few bubbles indicates very soft varnish - scrape it off, and heat what's left.

Use a sharp scraper. If the scraper doesn't take nice paper-thin curls of unheated varnish, your scraper is too dull. If the scraper tears at the bare wood, reverse direction, scrape the other way. Always scrape with the grain. ...


From Dan on Cruising World message board:
Heat gun and 1" red devil scraper to remove varnish. Soften the varnish and it scrapes right off. Follow with light sanding to smooth out. Make sure that you keep a honing stone close at hand and use it frequently to keep the blade very sharp. Summarized from "Building Your Dream Boat" by Charles E. Wood:

Make a "tack rag" to use after sanding and wiping, just before varnishing:Take a cotton cloth, dip it in warm water, wring out, sprinkle with turpentine, rub gently, shake out excess, sprinkle with a little varnish, wring out, shake out excess, let cloth dry for half hour.Store in a closed container.Renew by sprinkling with water and a few drops of turpentine and varnish. Use deglossing fluid to remove sanding dust ???How to varnish, summarized from "Building Your Dream Boat" by Charles E. Wood:

Varnish on warm, mostly windless days.
Prepare surface well. Wipe with a "tack rag".
Don't stir or shake the can.
First coat should be thinned.
Work from unfinished area to finished area.
Use as few strokes as possible.
Stroke in one direction.
Don't apply too heavy; it will sag or run.
Sand lightly between coats, and wipe with a "tack rag".


From Charlie / Bliss :
... I went to a Behr spar varnish - 3 coats on the exterior teak, two on the interior. Looks great and has held up well. About every three months I lightly sand with one of those foam sandpaper pads and reapply - it takes me about two hours total. I know that to some of you this sounds like a lot of work, but it really is not - I guarantee you that I am one of the laziest boat guys at the marina.

I learned my lesson in choice of brushes, though. At first I was using those 69 cent throwaways, bu the varnish looks a thousand times better when I use a 7 dollar top of the line brush. Only trouble is the cleaning afterwards. About varnishing with partial batches, from Colin Foster on Cruising World message board:

I use the clear two-part awlgrip polyurethane for varnishing so I often need small batches from larger containers. It makes a long lasting, hard surface brightwork job with just 3 coats, but it doesn't go well over conventional varnish - it has a tendency to bubble. It may not look as good as a fresh conventional varnish job but averaged over the 2 years (or more) I go between refinishing, the AVERAGE appearance over the period is far superior.

The polyurethane mixing ratios are usually not 1:1 so you need to take a tongue depressor type stirrer and mark the depth on it that you think you need - (which can only come from experience) - with a ball point pen. Divide the space below it with a second line in the ratio of the mix, and add a third line above it for the 10% or ?% of brushing thinner that you need. Since it always runs out when you have just a little more to do, the extra % from the thinner will get you through the job (Yeah, right).

In really hot weather I give the mix a head start by cooling the components in the refrigerator before dispensing, and avoid leaving the mix in the sun while using it. Pour each of the components in slowly to avoid bubbles so each reaches the next mark on the stirrer held vertically in your mixing pail. Have paper towels handy and wipe the screw tops and caps very thoroughly before replacing them. Then stir gently but thoroughly.

The manufacturers say to wait 15 minutes after mixing before using and although I usually do this, however I have not had any problems when I skipped it. When painting with a brush, draw paint from one side of the container, but wipe the brush out on the other side so the bubbles have to traverse the width before getting to your brush.


From article by Tom and Vicky Jackson in 4/2004 issue of Cruising World magazine:
Hard finishes last longer, but are more susceptible to cracking from movement, and more likely to lose adhesion if dampness gets under. Soft finishes are beautiful and flexible and more tolerant of movement and dampness, but wear more easily and are more vulnerable to UV and frost.

Two-part products: hardest and toughest finishes, but hard to work with. One-part polyurethanes: tough finish and easy to apply, but require many coats, and peel off from dampness. Synthetics (Cetol, WoodPro, etc) are easy to use, but require many coats and often impose their own color. Modern traditional varnishes (Epifanes, etc) are easy to apply and build well.

True traditional varnishes are soft and easily damaged. Oil finishes are easy to apply but don't build (so don't last) and often alter the color of the wood.
Always wet-sand; less messy, and won't get floating duct landing on wet varnish later.
Within reason, quantity and frequency of applications are more important than quality. Build thickness; don't worry about perfection.

In general, don't try to keep horizontal surfaces varnished; traffic, sun and damp abuse them.
Aim for 9 or 10 coats. Lots of thinner in the first coats. Wet-sand between sets of three coats.
A quick coat at the end of the season protects during the off-season.
Varnish while in the water: little dust around. Avoid windy days. Avoid very hot days (if you can't, thin even top coats). Don't apply in damp air.

Do the job quickly, using a reasonably big brush, keeping a wet edge.
Keep air out of the container before closing it up. Maybe add well-cleaned pebbles to displace air.