Shop Tips » Finishing
The Varnished Kayak
A majority of kayak builders finish their kayaks "bright," or with a natural wood finish. Wooden boats can be lighter and stiffer than other types, and with an entirely varnished hull you can show off how much prettier than plastic boats they are.
An all-varnish finish is a brave choice, however. Varnish will show every wart and misstep in your carpentry work, so you'll have to be wary of blemishes from the moment you start. Personally, I've always liked painted hulls with varnished decks, a tasteful approach that shows off both the wood texture and the hull shape. This approach also has the advantage of hiding my (frequent) mistakes.
Nevertheless, a clear-finished kayak is a worthy goal of craftsmanship and the "oohs" and "aahs" from passersby are worth the extra hours of sanding. And sand you will.
|How I Learned to Love Sanding
Paddling the seas
You'll spend more time sanding your wood-epoxy kayak than anything else during construction. Sanding can be seen as drudgery, or it can be a sculpture exercise, depending upon your outlook. Having built a hundred kayaks, I know that the quality of my finish work depends largely upon patience with the sander. Accept that sanding is going to be the difference between a good finish and a bad one, and equip yourself accordingly: buy a good sander, lots of sandpaper, a respirator, and ear protection.
A 5" random orbital sander will be all you need, the more powerful the better. I endorse the Bosch, Makita, Porter-Cable, and DeWalt brands. Bear in mind that they last a long time and you can use a sander for all sorts of projects, so a good one is worth the money.
A common mistake among boatbuilders is not changing the sandpaper frequently. This is deadly when sanding epoxy. Epoxy fills the sandpaper quickly, especially the types of epoxy that "blush". As the sandpaper fills, it stops cutting as easily, so the builder presses down harder on the sander to keep cutting. This in turn builds up heat between boat and sander, softening the epoxy so that it fills the paper more quickly, and so on in infinite regression. Change the paper often. Find a wholesale source and lay in a supply of 80, 120, and 220 grit paper, and expect to use it all. The discipline of keeping sharp sandpaper on the sander is rare outside of professional shops, but it's an essential practice for smooth hulls.
Epoxy sanding dust is a toxic sensitizer, so you must wear a mask. The high-end disposable dust masks (such as 3M #8511) will do for a short project, but the cartridge-type respirators are far more comfortable to wear. The vibrating whine of the sander can also be tiresome, so invest in a set of ear protectors or plugs. Anything that makes the job of sanding more comfortable means you'll stick with it longer.
Always keep the sander pad flat against the work. There's an urge to lift the pad and sand with the faster-spinning outer edge of the disk, but this will always result in a lumpy hull, often covered with unsightly half-moon shaped cuts that will glare at you through the varnish. Not cutting fast enough with the pad held flat? Switch to a coarser paper. On hard-chined boats, avoid the chines once you've 'glassed the boat, as the sander will quickly cut through the 'glass on these hard points. Use a hand-sanding block instead.
I start with 80-grit paper on a 'glassed and epoxied kayak hull, mostly concentrating on epoxy runs and sags and areas where the fiberglass cloth must be feathered. 120-grit is next, then I continue on to 220-grit. 80- or 120-grit paper will leave little swirl marks in the epoxy that will almost always be visible through the varnish, ruining or at best dulling the gloss of the varnish. You know you've sanded enough when the entire hull is a uniform cloudy gray, without little dark indentations in the epoxy indicating a low spot. Try not to sand into the 'glass; this may expose a weave pattern that shows up in the final finish.
Remember, any wooden surfaces that are to be displayed under varnish must be sanded up to 220 grit prior to applying epoxy and fiberglass to eliminate the swirls caused by the sander.
That's what it usually says on the varnish can, but these vague instructions hide a lot of methodical work. These days you have to think like a chemist to get your polyurethane varnish to stick to your epoxied hull.
Maybe, like me, you've had paint or varnish shrink away from an epoxy coating like oil from water, making an almighty mess of your kayak. This is actually a fairly apt description of what's happening: as they cure, many epoxy brews form a greasy film on the surface called "amine blush." This film is mostly water, one of the byproducts of the epoxy cure, and it's the very devil to stick paint or varnish to. You can wash it off, but the epoxy keeps curing, and "blushing," for a long time, so it may be advisable to let the epoxied hull cure for weeks or months before you apply the finish. A lot of people just go paddling with bare epoxy on the hull, but all epoxies lack UV protection and will break down in sunlight, turning yellow and brittle in time, so this is not a good idea.
One alternative to the amine blush aggravation is to use an amine-free brand like MAS Epoxy. MAS resin, used with their "slow" hardener, will yield a hard, clear, blush-free surface that you can sand and varnish within 72 hours if you have a warm shop.
With the epoxy cured and sanded, you should clean off the hull with some sort of solvent, an essential step to prevent the dreaded "fisheyes" in the finish. Most brands of paint and varnish have a proprietary "solvent wash," which I seldom use because it is expensive and hard to find. I use generic denatured alcohol and a clean rag to wipe off the hull, being careful to ventilate the shop and let the solvent evaporate for at least 30 minutes before applying the finish.
Some Varnish and a Place to Apply It
A bewildering array of varnishes are available for coating your epoxied boat. You should stick with a marine polyurethane varnish; "spar varnishes" sold in hardware stores aren't likely to have much durability or UV protection. Here at CLC we've covered scores of kayaks with Interlux Schooner Varnish, which we like because it's inexpensive, easy to apply, and has a nice amber tint.
A clean workspace is essential at this juncture to avoid the dreaded "nonskid finish". Every floating speck of dust in your shop will fly into your wet varnish, as if on cue, so you will have to go on the offensive, purging dust from every surface, including your own clothes. A puddle of water on the floor around the boat will prevent dust from being kicked up. Banish kids and insects from the shop.
If you're lucky enough to own an HVLP sprayer, know how to use it, and have access to a spray booth, you can stop reading here, because that's the way to go. Most of us will be brushing on the varnish by hand, however, so we should talk about brush selection. Largely out of laziness, I've forsaken my badger-hair collection for foam brushes. Foam brushes are cheap, disposable, and ideal for applying thin coats. The good foam brushes have wooden handles running all of the way into the foam head, without a plastic insert.
A glossy finish without brush strokes is a matter of brush technique. The objective is to apply a thin, even film. I varnish kayaks upside down, the left hull bottom and right hull bottom first, and deck last. The exact order really doesn't matter much.
Beginning at the bow, I apply the varnish with vertical strokes to an 18" patch (less if it's hot weather). Then, without dipping the brush in the can again, I follow this with lengthwise strokes smoothing out the vertical strokes. In this second step, it is crucial that the brush strokes go from dry to wet (right to left in the drawing). Never put the brush down into wet varnish. The vertical strokes get the varnish onto the boat, and the horizontal strokes even out the varnish. The "cross-hatching" pattern also virtually eliminates "holidays."
Without delay, repeat the process in the next 18" patch, overlapping the finished patch slightly to maintain the "wet edge," so that you don't have vertical lines where you finished one patch and started the next. Continue right around the stern, finishing at the bow on the other side of the hull. The varnish "seam" between left and right sides is on the keel and won't be ugly. I varnish the deck in one swipe, from bow to stern.
24 hours between coats is a typical drying time. You need a light sanding between coats, at minimum to give the first coat some "tooth" to stick to. It's also a chance to fix runs and sags before the next coat goes on. Before the final coat, I always wetsand with 400 grit. (Wetsanding, which requires special paper sold at any paint or hardware store, permits sanding with grits finer than 220.) The kayak will require a minimum of three coats for protection of the epoxy. It will start to look really glossy at five coats. More than 7 or 8 coats is probably overkill.
P.S. Now That You Have a Floating Coffee Table, don't be afraid to use it---I know of kayak builders who put their boats on display in their living rooms. The first few scratches will be painful, but after that, you'll remember that you have a kayak that is light, stiff, and fast on the water, not just gorgeous on the top of your car.