Varnish has been used for over 1000 years and still has a certain mystique. Well-applied varnish gives wood a glow and depth that seems nothing short of magical. But although varnish brings out the beauty in wood, varnishing all too often brings out the beast in the varnisher. I hope to convince you that varnishing is not difficult, just time consuming. If you can quiet your expectations for a quick job, you may come to enjoy the quiet, meditative process. I hope this guide will help you banish the beast and enjoy the process, or at the least the final result.
Marine varnish is based on tung oil and resin, with solvents (for good leveling and maintenance of a wet edge), driers, and additives that retard skinning (to give you a better “wet edge”) and enhance UV resistance. The oil is what helps varnish to penetrate the wood and the resin allows it to dry to a hard, durable finish. Ease of application, durability, clarity, color, and gloss are affected by these ingredients. The major manufacturers all have a stalwart product with die-hard fans – try a few and see which you like. In general stick to those called Spar Varnish or look at the ingredients and make sure it has tung oil, UV filter, and, generally, phenolic resin.
Before we start, let me give credit where it’s due. For a real expert go read Rebecca Wittman’s book, Brightwork: The Art of Finishing Wood – it is a beauty and she is the expert. For workman-like (rather than museum quality) results, my somewhat abbreviated method below is adequate.
A Straight-forward Method for Varnishing
Varnishing has four types of processes after the surface is basically clean and ready to go. (If you still need to remove old or peeling varnish, get a heat gun and read The Book, above). Please read about these four processes below the table before beginning. They are Preparation, Priming, Sanding, and Varnishing and are applied in the following step-wise order:
|Make sure surface is clean, dry, and sanded smooth to at least 120 grit
|Cut varnish with spirits 2-1 (two parts varnish, 1 part spirits).
|Wait 4 hours to next coat
|Cut varnish with spirits 4-1
|Wait 4 hours to next coat
|Cut varnish with 15% to 25% spirits
Wait 24 hours to next coat
|220 grit – lightly
|Cut varnish 10% – 15% spirits
|220 grit – lightly
|220 grit – moderate
|220 grit – heavy; surface should be completely white
|5-10 or more
24-48 hours to next coat
|320 grit – lightly.
After 7th or 8th coat wait at least 48 hrs before sanding to get a harder finish
Good sanding is the beginning of a top-notch job, so don’t skimp on those steps. I did say it is a time consuming process! Remember that you will never fix roughness or grain problems with varnishing, so make sure the sanding is beautifully and completely done before you start. For furniture grade and for rougher grains like mahogany, you may even want to use a filler to get a smoother surface. Read the Wittman book for these details. Otherwise, sand to at least 120 grit before beginning the varnish coats.
Use two coats of highly cut varnish for priming. To cut the varnish add odorless mineral spirits to the varnish in the proportions indicated. Use a cone strainer (right) to strain any impurities out of both the varnish and the spirits.
Sanding roughs up the varnish enough for the next varnish coat to stick and so is done before each coat of varnish is applied, after the previous one has thoroughly cured. You don’t need to sand after primer coats because they’re not slick. Light sanding just roughs up the surface a bit and heavy sanding leaves the whole surface white and powdery. Heavy sanding is only done after there has been sufficient build-up of varnish that there is no danger of going through to the wood. Use 220 grit sandpaper generally, but 320 once you start to build-up thickness. After sanding wipe down the wood to remove the obvious dust. Chamois is good for this or any non-shedding non-linting cloth. Cloth diapers work, or the big bags of cloths you find for automotive polishing or in woodworking shops. If you’re working outside you can can also wash down the item as long as there’s time for it to dry before you need to varnish. You will still need to rub it down with a tack cloth before varnishing, but there won’t be as much to remove.
How To Get Best Results from Varnishing
Easy Rules for Best Results
Varnishing requires good dry weather that’s not too hot. You also don’t want to varnish in direct sun unless it’s quite cool. Mornings are best, but make sure to wipe off any dew before beginning.
Use gloves. Latex or nytrile or any kind of thin disposable gloves. You will protect your work from the oil on your fingers and your fingers from toxins. Hardware stores, marine stores, drug stores, art supply… buy ’em cheap in bulk.
Always strain the varnish through a cone strainer into a disposable varnish pot. I find that small paper cups work well for small jobs, and you can buy disposable paint pots (use the small ones) at the hardware store for larger jobs.
Dip out the varnish rather than pouring. If you pour the varnish the lip of the can will get gummed up and be less likely to close tightly. Use a small silicone ladle like the one shown for greatest ease (available here at Amazon). After dipping just leave the ladle until it dries then peel the dried varnish off before the next use.
Keep air out of the can. Always close the varnish can immediately after filling the varnish pot. Close it tightly. If you poured rather than dipped be careful not to splatter as the excess in the rim is squeezed out. You may want to gently turn the can upside down between sessions. This puts the air / varnish interface, which will tends to thicken, on the bottom of the can. Later when you turn the can over and re-use it the top will be in good condition.
Just before starting to varnish use a tack cloth – a sticky, waxy cloth – to lightly pick up any dust on the surface. If varnishing outside you should tack whatever you’re going to varnish in the next 5 or 10 minutes to remove airborne dust. Leave the tack cloth at the end of the tacked section so you don’t forget to continue tacking when you’ve finished varnishing the tacked section.
Use high quality foam brushes sized appropriately to the size of the surface – 1” to 4” wide with 1” and 2” being the most commonly used. Do not try to re-use these to save money. The high quality brushes are sold in better paint stores – buy in bulk to save money. Cheap foam brushes are glued to paper around the wooden handle – poke up inside the brush to see if it’s paper or plastic. Only buy the ones with the plastic structure underneath. Some people use expensive varnish brushes – but then you have to clean them each day- and dispose of the dirty mineral spirits.
Methods for Best Results
Varnishing is more like pouring oil than painting – you’re just spreading the fluid in a thin layer, not trying to push it into the surface like you do with painting. Imagine the brush is a feather… Likewise the brush needs very little varnish to do its job.
Use sparing amounts – just dip the tip of the brush into the varnish. If the varnish drips as you move the brush – you have way too much on the brush. If the brush drags across the surface you either have too little on the brush or you have just varnished over tacky just-drying varnish. Avoid this – it makes ugly stripes.
Sometimes you’ll see tiny tiny bubbles as you varnish – it seems to happen more in warm weather. Brush these out gently, but don’t worry too much. The tiny bubbles seem to take care of themselves – they’ll have disappeared when you come back the next day to sand.
You can use reflection from the surface to check for dull spots that indicate “holidays” or missed bits. This is easier after there are enough coats to create a shine. If the varnish is not tacky you can brush over these. If it is tacky just ignore it – you’ll pick that spot up on the next coat. Better a holiday (blank spot) than a sag (which should be sanded out after it’s dry).
There are two ways to apply varnish – in “plaid” and “with-the-grain”. Plaid is used on the early coats to get good coverage; with-the-grain is used on later coats to get the best finish.
To apply plaid: apply the varnish in two to three stripes across the grain, then brush with the grain across your new varnish stripes from dry-to-wet to create a smooth seamless finish. This brushing first in one direction and then across gives plaid its name. The number of stripes you can apply before brushing out depends on the thickness of the varnish, the heat of the day, your own speed and comfort level. If the varnish is at all tacky when you go to brush it out, cut the number of stripes until the brushing out happens with no tackiness at all.
When you apply with-the-grain you don’t do much brushing out – just a few feathery swipes to cover holidays, smooth out excess varnish or catch sags before they happen. Always brush into the wet varnish – you do a sort of lifting of the brush before you get to the tacky parts brushed out in the last section.
Done varnishing for the day? Throw away your disposable varnish paint pot – or let it dry out then dispose of. DO NOT try to pour what’s left back into the can – you’re just introducing gunk into your clean varnish.
enjoy your work…