Boat Wood Varnishing
There are few things prettier in the world of boating than finely varnished marine wood.
Here's a varnish touchup tip, for those little dings and scratches that inevitably happen:
Take an empty fingernail polish bottle, clean it out thoroughly and let it dry, then fill it with some varnish of the type you used on your boat. The little fingernail polish brush is great for touching up small blemishes on varnish and preserving the waterproof surface. This helps prevent stains and potential damage from rot in the wood underneath the damaged varnish.
Varnishing wood on a boat is relaxing and rewarding. The look and feel of nicely varnished teak or mahogany enhances the appearance of any boat, even if it only has a little bit of wood. Keeping wood varnished is also an excellent way to make it easier to clean and to preserve it over many years.
Varnish will preserve marine woodwork in the condition it was in the day it was varnished. That means any blemish, residual stain, or dirt left on the wood will be preserved forever, so it is important that the wood be properly sanded and cleaned before varnish is applied.
Old varnish that cannot be recoated must be completely removed. I use a chemical stripper or a heat gun to remove it, then sand. If you leave the old varnish, it will look bright yellow underneath the new varnish, so be very thorough when removing old varnish.
If you are just recoating existing varnish, clean thoroughly and sand lightly with fine sandpaper. When building up coats of varnish, keep sanding to a minimum and use 220 sandpaper or higher. Always keep the varnish area as free of dust as possible. Each speck of dust that finds its way into wet varnish seems to turn into a boulder when the varnish has dried, and you cannot sand it out without losing the entire coat of varnish in that area.
Varnishing Over Oil
Contrary to what you may hear, you can apply varnish to wood that has previously been treated with oil. One of the main ingredients of varnish is oil, so the idea that varnish and oil are incompatible is obviously false. There are other chemicals involved, so it is a good idea to test your particular combination of oil and varnish on an unobtrusive spot to verify that there will be no problem with the varnish sticking and curing properly.
The only problem I have encountered when varnishing wood that was previously oiled is that oiled wood tends to gather dirt and dust and also tends to clog sandpaper. I like to give oiled wood a good cleaning with a scrub brush and some Dawn dishwashing detergent before attempting to sand it.
Choosing Your Brushes for Varnishing
I have used all kinds of brushes to apply varnish. I have learned the hard way why a good varnish brush costs more money: it's worth it. I have also learned that I can do pretty darn well with disposable foam brushes, so I use those. If you keep them well soaked and move slowly along the grain of the wood, the varnish flows on nice and smooth with few bubbles.
High-quality brushes for varnishing are more expensive, but do a much better job than the cheap brushes. The less-expensive disposable foam brushes also work very well.
If bubbles form while the varnish is wet, you can usually just blow on them and they will usually pop and even out as the varnish dries.
One of the reasons it is not a good idea to varnish in direct sunlight is that wood that is being heated will expel a little bit of air, which encourages bubbles to form as the varnish dries. Such a bubble is just like letting a piece of dust settle in wet varnish: it can't be removed without losing the whole coat of varnish in that area. It must be completely sanded out, or it will always be visible. If you must varnish in direct sunlight, do it late in the day when the wood is cooling off and drawing in air, and use some thinner to make the varnish flow more easily in the heat.
Applying the Varnish
Varnish should be applied in a smooth film, brushing from the dry area into the wet edge and then gently and evenly lifting the brush. Dragging a corner of the brush or allowing a drip of varnish to fall as you lift the brush are common mistakes, and avoiding them just takes practice. Try to learn on an unobtrusive area, and have a plan to complete the entire job while maintaining a wet edge. If it is not possible to maintain a wet edge, plan to make the "seam" where varnish coats meet occur along edges so it will not stand out.
Sanding between coats should only be done with extra fine sandpaper, and only very gently. Some people do not sand at all between coats, but just wipe down the previous coat with laquer thinner. Varnish will stick without sanding, but you can get a smoother finish with a light sanding.
It is critical that the wood be properly cleaned after sanding before applying more varnish. I use a minimum of 3 coats of varnish for interior marine woodwork, and at least 5 coats for exterior wood. Because the first thing to break down in the sunlight is the UV protection included in good quality marine varnish, look for a varnish with a high percentage of UV resistant additives. In the tropical sun, expect to recoat unprotected wood at least once per year.
Adding Non-Skid to Your Varnish
For special applications such as cockpit grates and cabin soles, the more durable two-part varnishes are a good choice. To add a little traction, I sprinkle a little sand over the second-to-last coat after it is applied, or just mix it with the varnish. Let it cure thoroughly, wipe down with solvent, and apply the final coat over the sand. It makes a good non-skid surface as long as the sand lasts, but does need recoating once it is worn down enough that the sand starts to come off.
A good varnish job requires careful preparation and meticulous technique, but for those of us who love the look of finely varnished wood on a boat, the reward of removing the tape and seeing perfectly finished wood makes all the time spent worthwhile.