The Perfect Varnish Job

(Or at least a good shot at it)

by Sherwood Heggen

The telephone rings. It is a fellow wood boater. The usual greetings are exchanged and then the purpose of the call comes out. The common question is asked, “How do you get such a smooth, dust free finish on your boat?” The question has an answer, but it isn’t short. Let’s explore that answer for getting a very respectable finish. Then, maybe you can answer the same question when someone admires the finish you put on your boat from the information below.

Let’s say that it has been three years since you have applied a couple of coats of varnish to your boat. The varnish is showing signs of drying out by having a dull appearance and the appearance of what seems to be fine spider webs on the surface. You have decided to tackle the project. You know you can apply varnish but overcoming dust in the finish has been a problem. The answer to the problem is preparation.

There are a number of ways one can prepare the boat for varnish, but the method described here has become my favorite way to get the job done very well. That method is wet sanding and clean-up. The wet method used is preferred because it controls the varnish dust from getting into the air and your lungs. Arm yourself with the following:

  • 320 and 400 grit wet/dry sandpaper
  • a good sanding block,
  • old terry cloth hand towels,
  • a large bucket for water,
  • high quality varnish,
  • tack cloths,
  • Jen brand foam brushes,
  • a stiff tooth brush,
  • a vacuum cleaner,
  • a great deal of patience … and
  • a compulsive-obsessive attitude about getting things clean.

The first step almost goes without saying. Remove all of the hardware from the hull. Please don’t tape around it. The end result looks so tacky. Take the time to do it right. The fewer obstructions you have to work around, the easier the varnishing will be.

Next, fill a bucket with water and load your sanding block with 320 sandpaper. Give the hull a good scrubbing with the sandpaper, changing the paper as soon as it loads up. Using the block helps level any areas where the varnish is not level or smooth. If you don’t mind dust in the air at this point, a random orbit sander works well. Don’t get overly aggressive in this step to avoid sanding through the finish into the wood. After the entire hull is well scuffed, it is time to wash away the sanding debris. Thorough cleaning is necessary to get a dust free varnish job. Wet an old terry hand towel with water from your bucket and wipe off the sanding debris. Rinse out the towel often and also change the water as often as necessary. During the preparation for the first couple of coats of varnish, diligently practice the cleaning part. This practice will give you reference for how much more thorough you will need to be to get all of the dust before you varnish. Be on a constant dust hunt.

Where will the dust hide? On the surface, certainly, but there are many little dips and cracks and holes in the hull that protect the dust from being picked up. You need to go in and extract the dust from where ever it can be. Deck seams typically are recessed below the surface of the deck and will hold dust when the deck is wiped off. Wipe out each seam full length with a wet towel a couple of times to get absolutely all of the sanding dust. Butt joints or any crack can capture dust and hold it until the sticky varnish brush comes along and draws it out of its place and then spreads it all over. Check for indentations on the hull, such as caused by rub rails or other hardware where dust can collect. Let’s not forget the hardware screw and bolt holes in the hull. Use a tooth brush to loosen and a vacuum cleaner to remove any signs of dust. As noted earlier, go on a dust hunt! Before varnishing, wipe down the hull again with a slightly damp towel at least a couple of times. When you can no longer see any dust haze remaining after the surface is dry, you are ready to use a tack rag to pick up any remaining dust. Yes, there is still dust remaining. Run the palm of your hand on the surface of the deck. You will feel minute pieces of dust which will seem to be boulders after the varnish is applied. How can that be?! You just cleaned up all of the dust! At this point, remove any clothing above your waist. Yeah, I know, that sounds weird, but, lint will continually be expelled from your shirt while actively moving about while varnishing. That lint will settle on the deck of the boat. Use your tack rag to wipe up the dust, gently passing the rag over the surface. Wipe in one direction like wiping crumbs off a table. Don’t rub hard with the tack rag. It will leave residue on the surface which may affect the varnish, or it could actually cause particles of dust to stick to the surface. Do this a couple of times. Now, wipe the tacky stuff from the rag off your hands with some naphtha and feel the surface again. It should feel like a clean piece of glass. If it does, you are ready for the varnishing.

Again, go on a dust hunt regarding your varnishing equipment. The brush, the outside of the varnish can, the container into which you pour the varnish, the area on the work bench where you have the varnish equipment and certainly the area around the boat must be clean. If the floor around the varnishing area isn’t already wet from the sanding and clean-up, wet it down now. This keeps dust from getting kicked up caused by the activity of walking around the area. The foam brush is cleaned with duct tape or a lint roller to pick up any particle of dust. Clean every portion of the brush. Go outside of the shop and blow any dust off the rim of the can. Wipe down the varnish can and the container for the varnish with a tack rag.

It is now time to varnish. At this point, it is not unusual to get a bit of an anxious feeling like before going on stage to perform. You just spent four hours sanding, cleaning and sweating and now it all comes down objective. Applying varnish to the hull to make a dust free finish. For the next 45 minutes or so, you must stay focused on laying the varnish on and spreading it out evenly and also stay in control of runs and sags.

So, here we go. Pour fresh varnish into a container from which you will apply the varnish. Small plastic throw-away food containers work perfectly for this. Using a separate container to dip the brush into, rather than the can, eliminates the chance of contaminating the varnish supply with dust. Dip the first half inch or so of the foam brush into the varnish. Start the varnishing process at an area where there is a natural break, such as, a deck seam or butt joint, because by the time you have varnished full circle around the deck, the wet edge that allows blending of the varnish will be gone. Dab the brush on the deck, leaving marks of varnish at four- inch intervals and brush through them in a two by two foot section. Apply the varnish across, rather than in line with, the deck. Once the varnish is spread out, brush through the varnish in line with the deck, making the strokes as long as possible in one direction. Spreading the varnish in two directions, ninety degrees from each other, will help to  eliminate what is known as a “holiday” or “skip” where accidentally no varnish is applied to an area. Be sure the varnish has been spread evenly, but don’t try to eliminate all of the brush marks. The natural leveling qualities of the varnish will do that. It might take an hour before the varnish really settles to a flat smooth surface. Now move on to the next area and repeat what you did before. Your final brush strokes will always be into the wet varnish to blend the two areas. Continue this effort until the entire boat is covered with varnish. Be on the constant lookout for holidays and sags and fix them before the varnish has a chance to set up. When you have finished, leave the boat undisturbed to let the varnish set up for at least 12 hours. When you come back, you should find a fairly dust free finish. If you do have dust, remember that was the first coat and there are at least two more coats to go to let you get it perfect. Try to determine what you failed to do thoroughly enough or what the conditions were that created the dust problem.

The second sanding will be done a little differently. Instead of using a sanding block, try using a wet hand towel folded to palm size with a half sheet of 400 wet or dry paper wrapped around it.
Why not use a hard sanding block? There are few straight, flat surfaces on most boats and the sandpaper will be effective only on the high points of the block. Using the towel wrapped with sandpaper, the paper will conform to the hull surfaces and will sand a lot of surface at once. Also, the towel should be dripping wet while you sand to help wash a way the sanding debris and keep the paper from loading up. It works great and only four to five sheets of paper are necessary for a complete sanding of the hull of a small runabout.

Sand the hull using this method and repeat the method for cleaning away the sanding debris. Apply the second coat of varnish in the same manner as before. Let it dry. Assess the results. Are things getting better in the matter of dust control? If so, remember what you did right and do it again, only better, for at least one or two more coats. Each additional coat will bring a deeper, richer looking glossy surface that you hoped for.

Now for a couple of tips on preparation for varnish. Sand the final coats by hand rather than a random orbit sander. Reason: Random orbit sanders can leave minute circles scratched in the surface. The varnish will conform to the scratches and reflect light. When looking at the surface, you can see something isn’t quite right. Hand sand with clean sandpaper and follow the direction of the wood grain. An even, smooth surface that reflects light properly will be the result.

Sand very lightly on sharp edges such as cockpit and hatch openings, transom and deck edges, etc.. Reason: it is extremely easy to sand past the varnish into the wood leaving you with a difficult stain and varnish repair to do. As hard as you try, there will likely be a mark remaining you can’t fix.

Occasionally, there will be small areas that need a bit more sanding after clean up is started. Rather than getting everything wet again, use a 3M scratch pad to lightly scuff the area and then wipe away the debris with a damp towel. Don’t get the dust airborne by blowing it away! If the varnish does not hold a wet edge or the brush marks don’t level out, add a little Interlux 333 Brushing Liquid. Five or ten percent thinner to varnish is a good place to start for the proper amount.

Here is the best tip of all. Practice. From the very first coat and each successive coat you apply, you have an opportunity to practice to make the next coat of varnish perfect. By the 14th coat, you should be nearly a pro.

A great looking varnish job is definitely a challenge to accomplish. The rewards are great though as you see people at the dock lingering to admire your boat. Go for it. It will be good for your ego.

If you have any questions on this matter or other restoration questions, feel free to give me a call. I can be reached at 715-294-2415 or

As always, don’t destroy; restore it. Good luck.