Finishing your Hull

Using an Autobody Shop for Clear Coating

 

 

 

 

Durable, Affordable Finishing

Wood is constantly undergoing slight dimensional changes in response to moisture content and temperature.

Sunlight warms the wood and the air in the wood expands creating pressure on the epoxy and glass and what ever finish you elect to use.

The air escapes through poorly sealed holes and unsealed end grain. When the wood cools due to declining temperatures, the air in the wood shrinks, creating a negative pressure. This draws air and moisture in the same holes and end grain as the pressure equalizes. Once inside, moisture causes the wood to expand. Given enough stretch/shrink cycles, the coating eventually cracks causing the finish to lift and peel from the wood. The exposed wood then discolors and eventually degrades. In the extreme, it will delaminate.

This is why it is important to eliminate places where moisture can find its way into the wood. This includes dripping/applying epoxy into any screw holes then running the screw in place. Quickly swab the screw hole with epoxy before running in the screws. This will stop the air from escaping and prevent water from getting in It is wise to apply wax or a mold release to the screw so you can remove the screw in the future. If you forget to apply some release agent to the fasteners, a soldering iron applied to the fastener head should allow removal.

I thinly coat the wood with epoxy to "bind" the wood fibers in the surface with a 1/8" thick foam roller. I envision the surface ply somewhat like a 1mm thick layer of 'glass cloth or mat. What I'm trying to do is "fill the weave." The Okoume marine ply is porous and soaks up the epoxy. After the epoxy has cured, I sand 1st with 180 grit to kill the fuzz then 320 to leave a smooth surface. The epoxy is mostly clear so the grain shows; it's still hard to see small surface irregularities. Doing this twice leaves a varnish or paint ready surface.

The varnish or paint finish not only protects the boat but does battle with UV rays. Good finishes are designed to address both stretch/shrink cycles and UV degradation. However the two forces in combination will eventually break down the finish and cause it to fail. The epoxy coating benefits by getting the protection from UV radiation that it needs. Epoxy and paint or varnish complement each other synergistically, the two in combination last longer than each coating would by itself.

Below is an Annapolis Wherry with "filler paint coat" being sanded away. The bow of the CLC "Lap Stitch" hulls have glass reinforced bow and bottom center planks. To hide this in the final painting you must fill in low sports.

The finish you choose also expands and contracts with variations in temperature. Finishes often fail near hardware mounting holes. Moisture finds its way in between the finish and the hardware, a result of thermal cycling (metal and wood expanding and contracting at different rates). If you are concerned about the epoxy curing, use a hair dryer or hot air gun to warm up the entire hull, staring at one end, and working your way slowly down the hull. This can be done a day or two after applying epoxy and prior to sanding

When finishing, ideally your shop will be brightly lit, possibly more so than while you were building. The best way to minimize potential dry spots, referred to as "Holidays" is reflecting light off the surface while you are varnishing. Nothing more maddening than finishing a great coat of varnish only to find you missed spots once you get it out in the light. A few days before finishing clean your shop. Sweep and vacuum everywhere a brush and vacuum will reach including everywhere around the heater won't send dust into the air if it will kick in. Use plastic sheeting and duct tape to block any drafty areas.

The Annapolis Wherry hull received automotive paint and was clear coat sprayed inside and out.

The shop and the hull should be warm before beginning. If the hull is too cool, the paint or varnish won't flow well. Make sure the epoxy is about 5 to 10 degrees warmer than room temperature to improve its flow properties. This can be accelerated by placing the can in a small basin of warm (not hot) water, stirring regularly. You may wish to have a practice surface to test before final brushing. On varnishing day, water the floor to hold down dust on the floor. carry in the canoe when floor is soaked. Immediately before beginning, wipe down the hull with a tack cloth to remove any dust that has settled from sprinkling water and walking around.

Supplies

I've become a convert to the disposable foam brush in the belief that the environmental impact of the manufacture and disposing of solvents used for cleaning brushes may be as damaging or more so than tossing the brush.

Fewer VOC's are released by not cleaning and the dirty solvent will eventually leech into the ground water somewhere. I keep a few fancy badger hair brushes which cost $40 to keep me humble. Pour varnish into new containers using paint filters to help minimize contaminates. This is especially true for re-opened cans.

Preparations for each subsequent coat of varnish should be the same as before, except that before the final coat, you can sand with 180 or 240 grit, or just steel wool. Apply the finish evenly without dripping, running, brush marks. After the second coat, I block sand with 220. The sanding pads you choose to use are a personal preference. Make certain the surface of any pad is consistently even with no undue ridges to avoid deep scratches. Be aware that pads will float over low spots and hollows. Start with pads and follow with hand sanding as needed. Sanding lightly between every coat assures good adhesion for the next coat. Then start to build up the coats. Five to seven coats will give you a good working finish. A show finish can be as many as 15 to 17 coats, with hand sanding in between.


The epoxy MUST be fully cured before you apply paint or varnish. A cool area at one end of the work shop (i.e. garage door) could cause one end of the hull’s epoxy to cure more slowly than the rest of the hull. If the epoxy is not fully cured, it is most likely the paint or varnish in that area will not cure/dry and harden. A fully cured hull should make a hard brittle sound when you tap lightly with your fingernail, just like the hull on a Kevlar canoe. If it sounds the least bit dull or heavy, it's not yet cured. High spots need to be sanded down. Low spots can be built up with another coat or two of epoxy on just that area. Wetting the hull with a wet cloth and looking at it from a very low angle with a strong back light will help you see any problem areas that need further attention.

Spraying the Finish

Varnish can be sprayed but requires the proper equipment and an understanding of how to use it. The odds of the first timer getting a sprayed varnish fish right the first time are remote. In my case, I go to a professional and have them spray the finish on. They know what they are doing and have the proper equipment.

Having an understanding the equipment and material are crucial to the success of a sprayed finish. Material has to be properly thinned to flow though the gun properly and the amount of thinner or reducer typically varies from different temperatures and moisture conditions,

You don’t really save any material spraying. In the end analysis you use up the same amount of varnish brushing as you would spraying if you have to thin the varnish to spray it and make repeated coats.The material needs to be thinned dramatically to get through the gun. With all the over spray and bounce back, the amount of material actually transferred to the surface is relatively low. Much of it ends up floating in the air until it settles on the floor or anything in the immediate vicinity. Until it settles and cures the over spray is highly flammable and potentially explosive.

Due to the shape and angle of the spray fan, material doesn’t naturally coat the surface evenly. Unless you know what you are doing it is difficult to get the material on the hull evenly with its curved surface. This is especially so in the tight confines of the inside ends of the hull. Since the material is so thin the likelihood of getting runs and sags in the finish is relatively high. It just can’t be helped. In general, work I get back from a professional still has the occasional run or sag which needs some light sanding and buffing. Still it is better than anything I imagine doing.

Safety in the spray area is critical. Not everyone is set up with the proper spray space. You certainly can't spray in the basement and have the atomized volatile product circulating around near the furnace or in a workshop with a wood stove or typical open flame garage heater. It isn't safe. Clean-up is a major operation. Getting the equipment clean and doing it repeatedly is rather time consuming ideally requiring some training and experience.

Painted Finishes

Primer has three roles; to serve as a binder for the topcoats, to fill very small holes. to give a consistent solid color base for the topcoats. After the first primer coat is applied, surface irregularities just jump out at you. This is the time to apply surfacing putty, filler, etc., to fill dings, gouges
Apply the filler as carefully as possible; it dries harder than the primer. If large bumps or blobs of epoxy remain, it is all too easy to sand through the primer when sanding down the filler. Consider adding color to the epoxy (it comes in white and gray) to get some grain masking as early in the finishing process as possible. When you inadvertently sand through the last coat of primer, reapply it to get the all important opaque base for the topcoats. I use white primer under light colors.

This Sawyer Summersong Solo was refinished with epoxy automotive body filler and
spray paint for plastics from a can.

Marine Paints

Is the extra cost worth the money? You decide. I believe the boats I build rarely if ever stay in the water 24/7. I like to believe my customers will exit the boat without running it up on shore. This is not always the case but if your boat is used lightly, the home builder may save a few pennies on paint for their hull. When using marine paint you want a very thin coating, apply with an 1/8" foam roller much like the epoxy rollers. Never re-coat until the paint sands to dust without clogging the paper. This typically takes 2 days, depending on conditions. The longer you let the last coat dry the better. Sam Devlin recommends a month if you can stand the wait!

Exterior Acrylic Latex House Paints

Latex paints have developed to the point where 100% acrylic latex paints can be as durable and tougher than oil paints. They resist chalking and fading, retaining their color especially well when exposed to bright sun. They are easier to apply, going on more smoothly and with less brush drag. They have fewer tendencies to grow mildew. They have almost no odor and no fire hazard. Cleanup is with water. They can be recoated in as little as one hour under ideal conditions. I currently don't use them for exteriors at this time however I have used them on occasion for the finishing coat on the interior of kayaks.

I've learned to coat the epoxy with acrylic latex exterior paints now and then to protect interior epoxy from degradation. The weather resistance of these polymers and all the top quality exterior primers, paints, and porch and deck paints is good, they don't seem very scratch resistant. But neither is bare epoxy and acrylic exterior paint is the least expensive protection available. Custom colors can be mixed to your desire and it is relatively quick to touch up scratches.

Thomas Firth Jones, “Dynamite” Payson, Jim Michalak, and Philip Bolger and even Chris Kulczycki reference using latex paint in their boat building books.

Here is the schedule. Sand the hull completely with 180/220 grit and clean up the dust.

Put on the first coat of latex primer. That raises the hairy fuzz. Let it dry a couple of hours then give it a once over with 220 grit to smooth the surface. Put on a coat of your exterior latex paint. Gloss is the toughest and most durable, but also shows surface imperfections best. Semi-gloss is almost as tough, durable, and easy to clean as gloss while not showing surface imperfections. For me, this would be the one to use. I've read it is better to stay away from the flat paint.

You won’t have to sand after the first coat of finish paint and you can easily re-coat in the afternoon. That finishes half of the boat. The next morning turn it over and repeat the schedule for the other half of the boat. If you use two colors on the outside of the boat, you will add another day to the painting. If you use different colors for the bottom and the side on the inside and have a steady enough hand to cut it in at the chine you can do it in one day. It is best to wait a week for the paint to dry hard.

"Canoeing alone is never lonely if all your friends have solo canoes"
Cliff Jacobson, Canoeist's Little Book of Wisdom