Kingfisher Drift Boat Build - Varnishing

Well, I've got the boat flipped back right side up and back in the paint booth. I've been taking a break from the boat for the last 3 weeks or so as I built a pole barn/shed out behind my shop. My brother Craig and his wife Toni came out and helped me build it. The weather in Idaho had shut him down so they came for visit and gave them a job helping me. I'll have a post about that process on another day.

So, right now I'm about three quarters of the way to a minimum of six coats of varnish to apply to all exposed wood parts on the boat. Ugh! I'm four coats into it and all I can say is you have to be patient and take your time. You can't be in any hurry. There's lots of prep, masking and sanding to the process. But most importantly, is the actual technique involved with the applying of the varnish.

Preparation

The first thing I had to do was to mask off the painted sides. I purchased a special 3M Scotch Blue Painters Tape for Delicate Surfaces #2080. This tape can stay in place for 60 days. I used this to mask a line right under the gunnels. I then used  48" painters masking plastic and taped it to the 1st layer of tape at the gunnels. This protects the entire paint on the exterior of the boat.

I next masked of the interior floors areas and sides that are painted with Durabak truck bed liner. The tape doesn't stick real well to the Durabak but I did the best I could.

Sanding

The Process. All the mahogany and oak parts on the boat have been coated with at least 3 or 4 coats of epoxy prior to starting the varnishing. The varnish job will be a minimum of 6 coats. I will work towards applying the initial 4 coats of varnish which will provide a solid varnish base coating. Once the 4 coats are applied I will need to do a real complete sanding of everything to make sure the surfaces are flat. It is necessary to wait for this heavy sanding as you need enough mil thickness to accomplish the flattening. Four coats should do it. Once the flattening sanding is done, I need to put on at least 2 or 3 finish coats of varnish. Sound pretty simple hey?

The initial sanding prior to the first coat of varnish and the next four coats is done using 220 grit sandpaper and/or a Scotch-Brite pad. I used 220 grit with a sanding block on the flat surfaces and the Scotch-Brite pad on the curved surfaces. I used the sanding block with the Scotch-Brite pads where I could.

Scotch-Brite pads come in various grits. I have primarily used the red pads (Fine about 300 grit). The Grey (Ultra Fine about 400 grit) will come into play on the final two coats. The sanding between the coats is mainly a scuffing to bond the next coat.

Sanding Reality - The main thing I have learned at this point is how the temperature of your workplace really affects the process. My shop has been getting down to about 45 to 50 degrees F at night. I keep an electric oil heater going in my finishing booth days and nights and have been able to maintain about 55 to 60 degrees F in the finishing booth. The main thing that the lower temperatures does is to delay drying time. The lower temperatures really only effect the time it takes to dry. My drying times between coats is running about 48- 72 hours. To be really dry it needs 72 hours. When is it dry enough?

Good question. You can "Hot Coat" varnish coats if the varnish is still soft without sanding. Sounds good doesn't it. I have been doing a sort of in-between. Let's call it a "Warm Coat". I've been letting each coat dry for about 48 hours and then using the 220 grit with a block to knock down the "nibs' and then block sanding with the red Scotch-brite pad. At 48 hours the coat is still soft enough the it clogs the sandpaper, but works well with the Scotch-brite pads.

To be able to sand with sandpaper the varnish needs to be hard enough to create fine dust and not clog your paper. In my case this will take a minimum of 72 hours, maybe longer. Being I am currently at my fourth coat I'm letting the 4th coat completely dry before sanding it flat.

Varnishing

Let me just start out with, "Varnish is intimidating as hell". There are hundreds of articles on the web with horror story after horror story about applying varnish. There are 4 important rules for varnishing that I have gleaned from the web and from to talking with experienced painters. Here they are and believe me I learned them the hard way.

(1) How you treat the varnish in the can
(2) How you get the varnish out of the can
(3) The brush that you use
(4) Your brushing technique

How You Treat the Varnish in the Can

Don't shake varnish! Varnish should always be stirred, stirred slowly enough that you don't whip it into a froth. If you shake the can or stir too vigorously you will be incorporating air into the varnish. Air in varnish is bad. You must stir varnish if you are using satin varnish as it has flattening agents that must be thoroughly incorporated.

If you are using gloss varnish you do not need to stir the varnish other than to incorporate added thinner.

Decant Varnish into a Smooth Sided Container

Do not apply varnish directly from the supply can. If you dip the brush into the can and then "scrape off" the excess on the lip of the can you will send a cascade of frothy varnish back into the can. This froth will be picked up with the next brush load, carrying a cargo of air bubble to your varnished surface of the wood. Transfer the varnish from the can into a smooth sided plastic container.

Thin varnish prior to application. I learned this the hard way. Thinning a newly opened can is impossible since there is no room for the added volume of thinner. Further thinning in the can is subject to inaccuracies since you can't easily determine how much varnish remains in the can. Only by decanting the varnish into a separate container can you accurately add the appropriate volume of thinner. The first coat of varnish should be thinned by 20% to 25%. (This does not apply if you are applying varnish over sanded flattened and epoxied wood.) Subsequent coats should be thinned by 5% to 10%. Thin after you have decanted the varnish into the application container.

Remember, the whole point of thinner in varnish in the first place is to make it easier to spread. The varnish needs to be thinned to adjust flow-out to current temperatures and humidity conditions.

By thinning varnish you are simply adjusting the viscosity of the varnish. Added thinner makes the varnish easier to apply by reducing the viscosity so that it will flow out and level better, thus allowing air bubbles to float to the surface and pop before they become encapsulated in the curing film. Brush marks will also level faster when the varnish is properly thinned.

One thing that lower temperatures in my shop contributed to is a thicker application of varnish. It has made keeping a "wet edge" difficult. I placed my can in hot water prior to starting but it just doesn't stay warm enough. Thinning will help solve this problem.

Use a Natural Bristle Brush Made for Applying Varnish

A varnish brush should have a good "reservoir" so as to allow you to "flow-on" a good quantity of varnish before you need to return to the container for more. Here's a contradiction to what you may hear. Never use a synthetic bristle brush or a "foam brush", or a paint pad.

A good test of a proper varnish brush is to dip the very tip of the brush into mineral spirits. If the brush wicks the mineral spirits up into the bristles, its a good brush. A "Badger Hair" brush is often recommended.

Brushing Technique

The brushing technique is very important. The varnish should be applied by "flowing" it in one direction. Never brush back and forth! If you are right handed begin at the left of am imaginary area about 12"  to 18" square. Make a single long stroke from top to bottom (across the grain). of your imaginary square applying light to moderate pressure. The bristles of your brush should flex slightly. They should not bend to the ferrule of the brush. Then, returning to the top of your initial stroke and using the same brush stroke, begin to drag from the top down. Once you have filled in your imaginary square, brush from right to left. from the dry to the wet (with the grain) to smooth and flatten the varnish.

Move the brush slow enough so as to not incorporate air bubbles into the finish. Continue in slightly overlapping pattern of brush strokes until you have covered the area. Tipping off in this fashion further levels the varnish and breaks any air bubble that may have become trapped in the finish. Again move the brush slowly. Brush only with the tips of the brush.