The Warmth & Beauty of a
Varnished Wood Boat
By Phil Spruit
When I attend any antique wooden boat show, the first thing my eye catches are those beautiful fine finishes on those truly classic hulls. There is something about the look of a well designed antique wooden hull, glistening on the water, with it's chrome or polished brass parts accenting their sculptured-like lines that strikes, I believe, all of us. The combination of natural wood and  man-made polished metal, to me is a very eye appealing experience. This article is written expressing my thoughts on the execution of the time honored, typical spar varnish finishing method used to achieve the deep warmth and beauty of those varnished wood boats. And some thoughts on one other possibility of finishing a classic wooden boat.

definitions & a few thoughts
First of all. Marine coatings for wood - a clarification. "Varnish" today is a generic name used by coating suppliers. Many years ago, varnish was produced predominantly by boiling linseed oil. In the last couple of decades, coating suppliers replaced real varnish with a solvent-based (and recently water-based), polyurethane-based material. This was done because polyurethane has overall, superior physical properties than the former "boiled linseed-based varnish". These 2 coatings are a completely different 'breed' from one another. Polyurethane is a petroleum-based derivative product. But the name "varnish" and "spar varnish" seems to have stuck with these marine coatings. I suspect marketing folks must of thought that the name "varnish" was a product that had established name recognition. So the chemical name was not used for the general public. Anyways, this article will detail the application & polishing of a "varnish" (polyurethane) coating. Which in this case, is a singular-component (non-catalyzed), linear polyurethane. These polyurethane coatings are very flexible, quite durable, (some coating companys also claim they are 'hard') quite the opposite) and adhere well to other types of coatings and to it's own type. They are relatively easy to apply by brush. But, as with most coatings for wood, never 'bullet' proof. The wood itself is the weakest link in this chain. Today, powder coatings & UV (ultraviolet cured) coatings are superior coatings versus what was typically used for wood. And because of environmental reasons, they are being use more today than ever in wood finishing. The harsh conditions of a marine environment has many problems for these types of coatings. The more traditional coatings of Lacquers, Enamels and Polyesters are of different "families" of chemical makeup. They will not be considered for this article. I would not recommend these types of coatings for marine type finishing on wood. This article also has a few thoughts on "automotive-type" urethane coatings that can also be used for wood in a marine environment. The coatings are the plural-component (2-part, catalyzed), hybrid, acrylic-urethane types. This product is fast becoming the preferred coating for today's automotive refinisher. I think they are a viable alternative coating for wood boat restorers who have access to professional spray & safety equipment.

varnish (polyurethane) vs automotive-type (urethane) coatings
After completing the varnish coating on my old hydroplane, I have come to the conclusion that the truth of the matter is the "automotive-type" coatings can produce a great shine quickly and can be applied in a lot less time than "varnish". They have had tremendous gains in their properties within last 5 years. The biggest benefits that I see are the one-time, one-day, multiple application of coats and ease of polishing. From an aesthetics point of view, these coatings are quite clear. So if you want to have that "warm" amber look of varnish, you will need to introduce a "amber" colored dye into the product to achieve the look of "varnish". They tend to have a "plastic" look to them. Just a side note, either of these finishing systems can be applied over epoxy coatings. And I would recommend surface preparation using this product. It has many useful properties that I will explain later in this article.
The drawbacks with "automotive-type" 'marine' urethane coatings are that you need to "professionally" apply this coating. That means spraying and all the precautionary steps that go along with atomizing a coating with air. Another factor is cost. Transfer efficiency of the coating product to the surface is poor. At best, about half of the coating is wasted in the air, due to the inefficiencies of spraying a coating. Another drawback is total film thickness. They tend to have much higher 'solid' contents. You can not keep piling on multiple coats of this product. Some coating mfg's state urethanes can be built up to about 20 mils (dry) thick, but I would never recommend going this thick on a wood product. These are 'harder' type coatings versus "varnish" and will have a greater chance of cold checking or spider web cracking with the greater movement of wood versus an alloy or non alloy type surface.

"Varnish" will be applied mostly with a foam brush, which means close to everything you paid for will end up on the lumber you are trying to protect. You can recoat very easily and you can apply many coats. The biggest drawbacks with "varnishing" would have to be the time length involved in the coating application and polishing. Because of the physical properties of this product that give you all the benefits described above, those properties also hinder the wood finisher. "Varnish" has a very long, dry-to-touch, cure time. And you usually have to wait 24 hours before recoating. And you need to resand (280 or 320 grit) before applying the next coat. If temperature and humidity are ideal, you can cheat and apply another coat over a 'fresh' coat, but you a taking a chance. And even then, only one coat could possibly be applied. The marine coatings just do not dry fast enough. Most of these coatings have a "window" that you can recoat in. And some of these coatings have a narrow time frame. Follow the mfg's suggestion. Practice on samples. The last thing you want to do is need to sand a coat off because of an adhesion problem. I've seen it more than not that when it comes to wood finishing, you will usually pay dearly in time & money with your attempt to 'cut corners'.

"Automotive" Coatings:
If you are going to apply the automotive-type coatings, and you sprayed the coating in a clean environment, you will not have much dirt in the coating. If you do not want to put any more effort into polishing, you're done. The coating will have a "orange peel" effect....but it will be shiny...similar to what the Detroit puts out on the new cars. But if you want a custom look, polishing will be relatively a simple process. These coatings are 'harder' and polishing-friendly. To get the 'mirror, wet look, wet sand with 600 grit and then 1200 grit. Followed up by polishing.

"Varnish" Coatings:
"Varnish" has a thin protective film that is floated to the top as the solvents evaporate from the coating you just applied. This abrasion resistant film helps the "varnish" prevent marring and fine scratching. If you decide to polish the coating, you will remove this protective film and your coating will be more susceptible to scratches. Also, these "varnishes" are probably the worst coatings in the world to polish. They are very "soft" coatings, which in turn, make it difficult to polish. Some "varnish" coatings are nearly impossible to polish.....they will have a "haze" to them after all your hard work. Remember, these coatings were not developed to be polished and thus the physical properties of the coating do not lend themselves favorable to polishing.

SIDE NOTE: For other arguments on this subject, click here to read an article on the Land O'Lakes Chapter of the ACBS website about this debate. It's titled, "Urethane-- A Viable Alternative to Varnish?" by Sherwood Heggen. This article explains some of the differences between using these two coating systems in a marine wood built hull. It sounds like it is still being proved out, but you will have to decide for yourself which is the route for your hull.

a flawless finish
Unless the last coat was applied in a perfect clean "coating-friendly" environment, you will have dirt, lint, and other airborne contaminents will float into your wet varnish coating during application and the relatively long, dry-to-touch cure time. The washing the floor, perfect time in the day or evening, and the other rules you hear and read about are never going to totally eliminate surface imperfections caused by the little dirt and lint buggers. You can minimize the amount, but you are fooling yourself if you think you will produce a totally flawless surface effect in a garage or outside. Detroit spent millions researching 'dirt' in their automotive coatings finishing rooms and found most of those were caused by humans. Lint from clothing being the #1 culprit. These studies help develop the self-contained, enclosed & dust-free spray booths. Robotics and deionizing areas for humans entering the finishing rooms minimized or almost eliminated these little dirt 'buggers'. "Automotive-type" coatings will be less prone to dirt and lint, because of it's physical properties, (they don't seem to be have the same "magnetic" properties as "varnish", but there will be, inevitable some dirt. With "automotive-type" coatings, those dirt particles can be removed more easily with spot polishing as opposed to polishing the entire hull. Varnish is nearly impossible to spot polish.

So be're not happy with the final result of your off-the-gun or off-the-brush coating.....

to polish, or not to polish
That is the question many of you do-it-yourselfer's ask yourselves after the wood finishing work is completed. Unless you are coating a flat one-dimensional level surface in a small amount of time, you will never achieve the correct, micro precision dry film that is required to produce the reflective effect of a mirror. The reasons why a mirror is so reflective (and I'm not talking about the silver nitrate that is applied to back of the piece of glass) is because of a perfect flatness of the glass itself. The fact that the glass is nearly perfectly flat combined with the reflective coating on the back combines to reflect light perfectly. No distortion in the reflectance is the sign of a quality mirror. Telescope lens take this reflectiveness to the next level. Same principal applies to any coated product. Most coatings are applied with brush or spray, and that, combined with solvents that help smooth and flow the coating out in an attempt to achieve that 'perfect' film level. But you will always have a "orange peel" texture to the surface and this will distort the reflectivity of the coating. You can see this by sanding the surface by a blocking the coating will very fine sandpaper. This will dull the high spots and reveal the amount of "orange peel" texture that is impairing the final goal of a perfectly flat, reflective coating. Without sanding and polishing, the coating's brilliance, shine or reflex can be high.......but to what degree?
There are instruments that measure this and assign a number on a scale rating. We use them in our shop. The Gloss Meter instrument reads this by bouncing a light off the surface and measuring the amount of reflectance. But the difference that can be achieved between a shiny pebbly and a mirror effect is the refinement of the reflective surface.  Usually, an acrylic enameled or urethane surface that is sprayed well will score a higher gloss level than a polished to perfection, glass-like surface. So the machine sees a difference of gloss but the machine cannot 'see' quality difference. This is the difference you can see from a factory applied coating and the custom applied coating. The difference being - the surface imperfections have been removed by the sanding/polishing process. So when you see a "shiny" coating out there and you're amazed at the brilliance. LOOK CLOSER. Judge the coating by it's reflective qualities. Next time you are at a classic car show, look at yourself in the coatings of different custom paint jobs from about 3 feet away. Are the details of your face as crisp as when you look into a mirror or are they slightly distorted by a pebbly effect? If they crisp and clean like looking into a mirror, then you are not just viewing just a shiny coating, but instead a very refined work of art. Years ago, it was rare to see this quality of work on custom paint jobs, most of them were done with many coats of acrylic lacquer and polished out to perfection. But today, with the improvements made to automotive coatings, it's rare to see a car at a show that isn't painted and polished to perfection or very close.

Moonshine Baby H-54 was clear coated with Z*Spar Flagship #2015 "Varnish".

The graphics were sprayed with white & black acrylic enamels (2-part) over the top of the Z*Spar after the clearcoat was cured & polished.

I want it as perfect as I can get it
Unless you have tons of more time or some more money to spend, perfection is a lofty goal to achieve with clear coat wood coatings. The fact is you are coating a piece of wood and wood was a living organism composed of a cell structure will always move in the course of time. Any coating will only be as perfectly refined as the structure it goes on. Temperature and humidity changes will move almost any structure a coating is applied too. Even a mirror (the silver nitrate on the back of the glass and the glass itself) degrades over an extended time. Wood will continue to have movement, expanding and contracting. The coatings for wood have more elastomers in the coating recipe than most other coatings for this. This helps the coating stay pliable during the surface contractions (a good thing). But this also means that all your sanding and polishing work will eventually degrade slightly with time. It will eventually form a "orange peel" texture from this movement. Although, it will never degrade to the degree of an off-the-gun or off-the-brush application of a coating. That 'orange peel' texture will eventually get worse.

so what gets me close?
A little thought, some extra time, money and alot of 'elbow grease' will go a long way. If you have never attempted wood finishing with marine coatings, practice on some samples before starting on your wood hull. About 95% of your time goes into surface preparation prior to the coating application and/or polishing. Don't butcher all that hard work because you think you can wing it along the way. Your final result will convey this.

before you start
First......again.....make some samples......Perfect' everything on your samples before proceeding. I think most folks will be glad they did. It will give you the satisfaction of knowing what you are going to end up with. It will also allow you to make changes, especially with the color. With your samples, you can figure out what sanding steps are required, (and which sanding steps are NOT required), amount of stain and strength needed, proper amount of time to leave the stain on before wiping off, diagnose potential problems with sealers, and topcoats, (and polishing....remember certain "varnishes" will produce a haze). If you want that look, now is the time to find the correct "varnish". Peace of mind has it's dividend's. With wood finishing, it's best to find all the "surprises" on a scrap piece of lumber and not your prized hull. You can make changes easily with samples. On your sample, mask off each of the steps you take with masking tape, after you complete the sample, removal of all the masking tape will give you a "Blueprint" for your wood finish. Remember.....after it's all're the one who is going to have to live with the results.

surface preparation
Sanding....If you are finishing plywood, look at the thickness of your top "ply". This top veneer of the plywood, even from the same manufacturer, can and will VARY. Be sure you have enough "meat" to work with if you are going to sand with a heavy grit. By the way...a few years back the American panel manufacturers were going to adopt the European standards for veneer thickness. Most European & Asian grades of plywood for furniture have a 1/40" veneer thickness. Americans opted not to go to this standard and stayed with the 1/28". This is good. It is almost impossible to refinish (from the sanding that is involved) a Non-American made veneered panel. Producing quality marine grade plywood was given up being produced by the American manufacturers. Fortunately although, with marine grade plywood produced by the Europeans, I've found there is a significant thickness on the top ply, face veneer, closer to 1/16". They were thinking. But look first before proceeding.
Sand only enough to get out the surface imperfections. If you have a scratches and dents, soak a towel with hot water and apply to the scratched area. This will raise the grain and in most cases lift the surface of the veneer or lumber so you can sand out the area level. Don't trying sanding out imperfections without raising the grain, you may sand through the face veneer, then you will have a real problem. Sand with the grain and a level block to support the sandpaper if using anything from 35 grit to 280 grit. Use the finest grit possible to remove imperfections. At 320 grit sandpaper, you can usually get away with a DA (dual action, circular) sander and not show circular marks from the stain that will highlight  the sander scratch pattern. You can use a random orbital sander but I prefer a non orbiting sander for this step. A straight-line sander is going to give you the best job, but they are slower. If you are not sure, sand with a block in the direction of the grain. For final sanding, this will not take much more time. Change your sandpaper frequently. Sandpaper is relatively cheap compared to your labor time. Silicon carbide coated on the paper is best for wood. But the "sharpness" of the silicon carbide will degrade quickly, so again, keep changing sandpaper for the best, most even results.  Another note - Quality sandpaper is a must. If you have ever compared different mfg brands of sandpaper you will know why. Don't be cheap - you get what you pay for. For the lower grades (up to 120 grit), there is not much difference between manufacturers, these are essentially "filing" grades of sandpaper.
Remember, your stain work will only be as consistent and even as your last couple of sanding operations were.

a few other notes worth mentioning...
Before you start sanding, "wash" your hands with wood dust. If you have any oils from your hands on the wood surface, wash the wood area with Naptha. Also, another "trick" used by wood finishers is to pour Naptha on the entire wood surface. It will give you a visual look of what the surface will look like after all the clear coating is done. It will show up everything.
When you happy with your results and think it's time to apply some stain (or sealing the wood, if not staining), vacuum the dust off, then use dry, clean, compressed air to blow the wood dust from the wood pores. If you use a tack rag, wipe very gently. That's a shellac-type of product they impregnated into that cheesecloth that makes them tacky and this product will show up if any gets on the wood surface when stained or varnished over.

applying the wood stain...
SAFETY First. With most stains, you're dealing with flammable solvents. Protect yourself, your hard work, and your prized possessions. Make sure environmental conditions are right.  Next make sure it is warm and dry out. After you have practiced on your samples and think you are ready to color that wood.......remember....this is not a race. One of the reasons it is hard to get anybody interested in wood finishing is because it's very dirty work. Most people just want to get it over with. So take your time and be very methodological towards this operation. Try to apply the stain inside or at least in the shade. Lighting is critical. Have lots of it. Many a bad finishes were due to poor lighting. Also...view your work from different angles to 'see' it all. You probably don't want to see any surprises when you're done and take it outside in the bright sunlight.
The staining application operation will work the best with 2 people when staining a very large object such as a boat hull. One to apply & one to wipe off the excess. If working by yourself, map out your strategy. I stained my hull's bottom first, followed by the sides, chines, and sponsons. Using all natural breaks in the hull to your advantage. After all finishing/topcoating/ rubbing is completed, then flip the hull, mask off all your finished work and then finish the decking.
From your samples you will already have figured out a time to let the stain sit before the wiping off operation. Make sure your stick to your schedule. Generally, wood will only absorb so much stain. But stain formulations vary, so follow your own time schedule. Apply the stain in a circular, downward movement, making sure you are getting it's pigments loaded into the pores really well. If you did larger samples you will have figured out that. Stain wiped off too early? The stain may not give you an even coloration of the pores and may look spotty. Some stains, if left on too long, can darken the wood past where you wanted it.  If this happens, you can lightly steel wool or scotchbrite off some excess, but be careful. This effect can look different than what you are trying for. Most wiping stains are formulated for a "clean wipe". All excess stain is removed. Make sure you have many absorbent, lint free rags available.
The stain is going to bring out all imperfections. If you missed a scratch or dent, sand it out now, yes....during the staining operation, if you wait until after the stain has dried, and then try to fix and restain the area, you will have a "halo" around that repaired area.
When you done, stand back and thoroughly go around your hull looking for areas that don't look right. A even application, followed by a clean, even wipe will give you the results that you achieved with your samples.
Most wipe stains require an overnight cure. Follow this direction. If you start applying your clear coats before a complete cure of the wiping stain you will probably have adhesion failure.
One Very Important Note: Wet all your rags down with water if you used a solvent-based stain when you are done staining. The oils used in these stains can, and will, self combust if compacted enough and not given enough air to dry. I've seen many fires in the finish room, because of this. I am always surprised this is not even written on some brands, or the ones that are supplying this information, written larger on solvent based stains that are sold to the public.

sealing the wood prior to topcoating need to seal the wood and allow gases that are in the pores of the wood to escape. Mahogany and Oak are two wood species that have deep pores and need to gas out as the first coat begins to cure. Species like maple and cherry do not have pores that are very deep and are not as prone to this phenomenon. What is happening here, is the sealer coat is "forming" a skin on the top surface and the gases have not all escaped from the wood surface. As the gas tries to escape, tiny bubbles will appear in the first coating. These are commonly known as blisters. You DO NOT want these, as they are nearly impossible to remove without starting all over. Even a no-stain finish can show these. Do not start piling coatings on the surface thinking these will disappear. You will only make them worst. Sand off and restart. If you prepared you samples first, you would have seen this and prepared your sealer accordingly.
Secondly....humidity level....if it is humid out, you will get water trapped in your clear coat as it dries. Do yourself a huge favor and wait for another day. Moisture trapped in the coating will look like a white haze or a bloom. Another mistake that requires a full stripping and sanding. If you have some "blooming" after the clear coat has cured to touch, you can heat up vegetable oil and pad the surface. This will resoften the coating and allow the moisture that is trapped to escape on certain coatings. Another old trick that still works with even today's hi-tech coatings. (I remember my mom crying after she ironed a shirt on top of some towels on her new coffee table. I cooked up some hot, not boiling, oil and showed her how to fix this dilema. This also works for water spots on your furniture). After any clear coating, move the object indoors or put up a tarp. The nighttime dew sitting on any freshly clear coated surface, even after 16 hours, may "bloom" the coating.

sealing the wood with epoxy prior to topcoating
The sealing step is where I like the epoxy coatings. You may use this product under either clear coating system you are electing to use. With a stained hull, the best property of epoxy is two-fold. The first being, it can go on most open pored woods, full strength, with out 'blistering'. Just make sure you apply a very thin film for the very first couple of coats. No excessive rolling or brushing here, you might want to use foam brushes for the first few coats.
Secondly, epoxy has very high build, and you can apply multiple coats after the product has reached a dry to touch state. I started in the early morning and applied as many coats of epoxy as I could before the work day was up. After a 24 hour cure, you will have a encapsulated finish, with the chances of sanding through this finish very remote. You still want to be cautious around edges and corners when sanding, but for the most part, you have just "locked in" all your staining and woodwork with a very thick, hard, and durable film. If you have ever sanded through the stained finish, you'll appreciate this property.

After preparing the coating for topcoating by sanding, vacuum and tack off the dust. If applying "varnish", I pour out a line and using a wide foam brush, work left to right out from any end. I worked out about 2 feet and started the next row. As I near a wet surface I lightly overlap the previous coating. Add solvent, (as, and/or if), required to get a level and even flow out. Work quickly and try to get a heavy and even coat applied without runs. temperature and humidity levels, work indoors and try to keep bugs to a minimal. I have no suggestions for bugs other than if you have the luxury of time, coat before they arrive in the spring or after the first hard freeze. If they are just 'build-up' coats, don't sweat it, as you cn sand them out before the next coat. For final coat, if you are polishing your coating, no problem, but watch your coatings flash and have a fine, needle-nose, or hemostats, ready to pluck them from your wet surface. I also found that having screens in your garage windows work. Try to keep as much fresh air coming in as possible for the finisher.
Air dry at least 24 hours. If you had any runs, use a razorblade to scrape then out. Then, sand with 320 grit and a block for those areas. Now go over the entire coated area. I sanded this step with my electrical, random orbit, palm sander. I've had this Porter Cable sander for 20 years now and it is the only time I have found a good use for this sander. It does a fast, near perfect sanding job with these "varnishes".
"Automotive-type" coatings, follow product data sheets directions. You will need to ask for these when you buy the coating. They are usually not labeled on the can. Generally, you will apply 3-4 coats total. Most people just keep putting on coats until they are just about out of coating.

how many coats do you want to apply?
Well, most of us would prefer just one but we're talking wood finishing you were thorough with your samples you will have figured this out. I went with 9 coats of "varnish" before I thought I had enough varnish applied. Most "varnishes" are about 25-30% solids. That means you will apply about 6 mils of wet varnish per coat. After the solvents evaporate, this will leave a 1.5 mil thick dry film. After sanding, you will have about 1 mil of dry film left. Multiply this dry film by 9 coats and this will give you a 9 mils total of dry film. This is a sufficient base for which to sand and polish out. Also, this film thickness allows for 1 additional refinishing jobs before reaching that 20 mil film limit for varnish. This will also make a good sanding base for those refinishing jobs years down the road. If you do not polish, this will give you a nice, deep look. By-the-way, most "automotive type" total dry film thickness is 6-7 mils thick and a typical "automotive coating" can have 2 additional paint jobs done before the whole thing will need to be stripped completely. But remember, I would not recommend this film thickness for wood. Also, I used almost 2 gallons of "varnish" to complete my 19' 7-litre hull.

"Automotive-type" coatings (because of their higher solid content) generally need only 3 or 4 total coats and can be sprayed right on top of the next coating, as soon as the previous coating is dry-to-touch. The big plus here is you are done in 1 day.

If you are handy with a spray gun, I would highly recommend you spraying the varnish for the last coat. This will give you the best look and make for a easier polishing job if going that route.

spraying the last coat with "varnish"
If you decide to go this route for the last coat, here's some tips for you. I recommend this, but you'll have to decide for yourself if you want to do this. Spraying a coating will always leave the best finish, bar none, to any coating application using liquids. But some skill is involved with handling a spray gun. You need nice, even, consistent movements. Runs, dry-spots, inconsistent  and an uneven coating will be your worse finishing nightmare. If you have even the slightest doubt with working a spray gun, I wouldn't advise spraying any type of coating. If you're confident, but don't have much experience with spraying, again make samples, something 3-D, if you're happy with the result, go for the hull. It helps to think and move like a robot.
My favorite spray gun for applying the heavier viscosity type coatings were the old Devilbiss MBC spray guns. These babies could atomize most coatings into very fine particles for the perfect finish. They have not been around for a long time. But the standard automotive refinishing spray gun handles the varnish very well. The spray gun I predominately used was the Devilbiss #JGA-502-30EX (30EX being the cap and needle size), which handles reduced varnish just fine. This gun has been a standard in the automotive refinishing industry for quite a while, until the new technology came along. The JGA was a "conventional" spray gun that produces good atomization, but transfer efficiency is not very good. HVLP (high volume, low pressure) spray guns would probably work if you have one and can get alot of product through the gun with some very large tips. I personally don't care for them for small batches and staining work, (mostly because I don't like the atomization of the finishing material) but they are standard issue in California because of the state-mandated, transfer efficiency ratings these spray guns produce. We use HVLP in our high volume (topcoating) area in the finishing room. They use high amounts of air at very low pressures to atomize the spray. This helps the spray not "bounce" off the surface you are spraying. If I had this set up in my tool box, I probably would have used it. If you have a spray gun in your toolbox, try it on some samples and see if you get a smooth, heavy, and even coat applied, which is the main objective here. No sense in buying a new tool if you have one that will work. I get a kick out of seeing all the ads for these fancy and outrageously priced spraying equipment setups you see in the various do-it-yourself magazines. They also have these wild claims to 'em....Snake your money if you don't own a spray gun yet. Just buy a standard gun like above..about $200 bucks with a 1-quart spray cup (you'll spend a little more with the stainless spray cup). It's very versatile and well rounded for general spraying. The spray gun has all stainless passageways throughout the gun. This will allow you to use it for water-based finishing products and you won't have to worry about rusting anything. If you clean them up right after each use, they will last you a lifetime. Adjust the solvent reduction until you achieve the right "smoothness" to the coating. Keep adding reducer just enough to spray a level coat and no more. Warm the "varnish" if its cold out before spraying. (Careful, you're working with big-time flammables here). A glue pot works best. It will help lower the viscosity to a sprayable consistency without having to having to reduce with too much solvent. Which with varnish, will be predominantly mineral spirits. I also added in some naptha, which is a much faster evaporating solvent than mineral spirits. (Old School was - 50% Naptha & 50% Mineral Spirits is roughly what lighter fluid is). The key here, being to get a smooth, level, and heavy coat applied, with no runs...that's the trick, isn't it!. If you reduce (or thin) the coating too much, you will not get enough of a dry film left on the surface to cover and fill in the 320 grit sanding scratches and this is not good. Use a fine mesh strainer when pouring into your spray cup. Double then up. Spray outside with just a light wind. Move any vehicles, pets, and children. Varnish spray droplets are big, sticky, gooey, blobs just waiting to ruin anything it lands on. If you don't like your neighbors, this coat you are spraying will surely piss them off, so plan accordingly. (That's why I live in the country).
Save your lungs and wear a cartridge-style, organic respirator. Wear old long sleeves shirt, hat, and a pair of pants you don't mind ruining. Or better yet, buy a cheap Tyvek suit for a few bucks. Use disposable surgical gloves. I always have a box of these in my nitrale works good. If you wear glasses, they will be 'spotted' after you put this coat on. You will have a nice ring around where your hull was in the driveway, so prepare for that unless your wife doesn't care how that looks. You are going to probably be breaking a few environmental and fire-safety laws, so you didn't read this here. PERFORM this at your own risk!
Figure out which way the wind is blowing and have it blowing on your back. Start spray direction close to you moving right to left, back and forth, with moving the gun away and spraying so all the overspray falls on the area that you are about to spray. 50% overlap each spray pass. Set your air pressure, at the gun, for about 50-65 pounds. "Varnish" typically likes to be sprayed at a higher air pressure than alot of other types of coatings to get a good, even coat. Open up the material control valve on the spray gun most or all the way and adjust your fan width to give you a 8" width at about 8" away.cure timeFor "varnish" I would wait at least 30 days before polishing. If you know you are going to polish, you can sand after about 2 weeks and this will open up the pores in the coating and promote a harder and faster cure. But still, let it sit for another 2 weeks.
If you used an "automotive-type" coating, I would start sanding and polishing in about 14 days.

final sanding before polishing
With "varnish", you should be able to start with 800 grit if you sprayed the last coat. If you applied the last coat with a foam brush, experiment with 400 or 600 grit to see if you need to go this route. After 800 grit, I followed up with 1000, 1200, 1500, 2000 grit. Sand with rubbing block and a spray bottle full of warm water. Keep the surface wet and do not push down on the block, let the sandpaper do it's job. Human spit aids greatly in lubrication for this step. My wife was laughing at me as I was spitting all over my hull, but that's were the "spit-shine" term came from. Start a 2'x2' area. Get a squeegee and use it to see what you are doing. Buy a large box of diapers. The old style, 100% cotton, washable ones. These are getting harder to find. Completely sand the entire surface before moving on to the next grit. When you have completed that grit size, on the next grit size up, you will want to sand in the opposite direction. This method allows you to see easily that you have removed the 'scratch' pattern from the previous sanding step. Keep the surface clean, with these fine sandpaper sizes, you do not want to get a chunk of anything that will gouge the surface.
On the 2000 grit, you can sand in a circular motion with the sandpaper and sanding block. Keep the bottom of your sandpaper clean. You can usually 'feel' if a bigger chunk of something gets on the paper. Remove it immediately by getting fresh sandpaper.
With "automotive-type" wet sand with 600 grit and then 1200 grit. You may need to finish up with 1500 grit depending on the coating you used. To determine this, sand a small area with 1500 grit and start polishing equally on both grit samples and see if you need to sand with 1500 grit. If there's hardly any difference, you can forego another round of sanding.

The buffer I use is a Milwaukee variable speed 0-1750 rpm. I run it at full rpm. The guys at the shop use the Black & Decker, because they make the lightest's polishers that we've been able to try. I would not recommend a faster RPM for varnish. The bonnet I have always used are called Round Up made by SCHELGEL. Part #890C. This bonnet has a 1-1/2" pile. These are like the old lambs wool bonnets. You will want the bonnet that is held on by a nut in the middle against the hard rubber backer for the bonnet. Do not buy the tie-on ones that have a string that attaches it to the pad. Any good automotive body supply shop should carry these, they have been around for years. If not, the 3M bonnets work okay. I would get two bonnets, one for the actual buffing and one for cleaning up.
To get the feel of a buffer and if you have never polished a coating out before, maybe try to use the foam 3M pads.....they were developed more for the 'rookies' at the body shops. Their best feature is it makes it hard to "rub through" the coating. If you're quick to learn and want the professional machine, use the bonnet with the heavy pile and hard rubber backing pad. Just go easy near those edges. Also, square inside corners are impossible to machine buff, so plan accordingly. The polish I use is 3M FINESSE-IT II part #051131-05928. This will be the only polish you should ever need. You will want to buff outside, preferably on a somewhat windy day. You will have lots of lint flying around. Work a 2' x2' area. No more, no less. Squirt a bead about 4" inches long for that area. You usually need 2 applications of compound over a 2' x 2' area up to the gloss we all want to see. Clean up the bonnet often. It should not be saturated (wet) or crusty (dry). To clean the bonnet, hold the machine between your thighs and take a screwdriver and hold it about 45 degrees to the pad. Power up the buffer at full speed and move the screwdriver up and down. HOLD ON TO THAT SCREWDRIVER! They make a "spur" for cleaning bonnets, but save your money. The screwdriver works just fine. You will see the pad clean up as you move it back and forth. Get used to cleaning your pad after every 3-5 applications of polishing compound. You will see that cleaning the pad often will help you keep that pad nice and fuzzy. Do not polish on the same spot very long. Keep moving the buffer around left to right, then up and down. Use medium pressure when you first start the buffing, then light pressure as the compound fades away. Feel the surface right away. Is the surface too hot? It should be slightly warm. That's it. Following these directions should bring the gloss up, with a haze-free effect. If it's got a haze to it, you didn't recognize that in your sample that you should had made to confirm you have a "buffable varnish".
If it is an "automotive-type" coating you are polishing, you will have no problems if the coating was properly catalyzed, reduced, sprayed, cured and sanded properly. It will polish out with ease compared to the "varnish" coating. With these catalyzed urethanes, you can polish at a higher speed (up to 2600 rpm).

clean up
Get some 3M Perfect-It Hand Glaze part #05997 or 3M Imperial Hand Glaze part #05990 (available at the local auto body supply shop) and using more of them diapers or sweatshirts. Apply it like a wax. Wipe on, let it haze, and then wipe off with a clean cloth. This will even out the polishing work and swirls and provide a protective coating to your surface. Apply this material whenever detailing is needed. It's good stuff.

That's it! If you took your time and did everything yourself, you have learned a new trade, probably saved yourself about $5000 bucks, and if you were thorough, should have the concours quality wood boat finish.

The cowlings for H-54 are custom built from a fiberglass substrate by the original owner long ago. I repaired them and primered with an epoxy primer, (surfacer-type product) followed by the old 'standard' Ford Candy Apple Red acrylic enamel (2 - part). I put a clear coating  only over the gold leaf portions, not the red. The cowlings are very old and still somewhat fragile. They will  continue to need rework as the years progress. The inside of the cowlings were topcoated with 'trunk paint' (aerosol) to help hide the roughness that can be typical with old cowlings.
The interior of H-54 was sprayed with Valspar Marine "spar varnish" which I purchased at my local "Fleet Farm" store. I did not see any added benefits to using the high $$ "varnish" for this part of the restoration. It should stay relatively dry inside compared to the outside. And after the decks are secured, is not going to see alot of the harmful UV rays from the sun that can ultimately damage the coating. I masked the outside bottom of the entire hull off and started spraying this new fast drying version of polyurethane. About every 20 minutes, this solvent-based coating would be dry-to-touch, and ready for it's next coat to be sprayed. I was impressed. I started about 8:00 and and was done just before lunch. I lost track of how many coats I layed down, but would guess about 5-7 coats were applied. It looks great, but of course, most of what you see is new wood. If I was restoring a vintage hull. I would recommend applying at least 2-3 coats of a penetrating epoxy (like CPES) to the interior of any hull before topcoating.

A discussion took place on our board and a point was made to use a more durable coating on the inside of the boat that can resist solvents from the motor (ie - gasoline, methanol, oil, etc.) I totally agree with those comments and would recommend upgrading to a more solvent resistant coating in lieu of using the 'spar varnish' type product or maybe just apply the last final coat(s) with a more solvent resistant coating. I had some standing racing gasoline that wasn't immediately wiped up and it did soften & lift off the 'varnish' coating.

About the author
This article is based on my experience with wood finishing for the last 35+ years. (My day job).
I've also worked with and finished my hobby vehicles in lacquer, epoxy, enamel and urethane over the years.
When I decided to rebuild a 1960 7-litre hydro, one of the things I wanted to come away from
with from this experience was to learn what it would takes to apply an old fashioned deep warm varnish finish
to a wooden boat. I now have a new found respect for these fine marine finishes.
Best of luck to all the do-it-yourselfers (like me) who believe in their abilities & like the challenges. 

You can read my short bio here. ©2002 (revised 2004 & 2010) Phil Spruit

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