Finishing in Cold Weather – FineWoodworking

Applying finish is one of the more difficult parts of cold-weather woodworking. For most finishes, there is a temperature—usually around 55ºF or 12ºC—beneath which you should not proceed. But even when your winter woodshop is heated above the minimum threshold, the climate will still affect the performance of the finish.

First, temperature will affect a finish’s viscosity, or resistance to flow. At lower temperatures, the viscosity of a finish may increase making it thicker, like honey. At higher temperatures, a finish may be thinner, like milk. Generally speaking, a thin application of a finish will give you a more even coat and better results. So in a colder climate, you may have a harder time applying that perfect, thin coat.

Cold temperatures will also extend drying times, meaning you may need to wait longer to apply a second coat. If curing is an oxidation reaction, it will also slow in decreased temperatures. Take the Tung Oil sold by Real Milk Paint. The typical dry time for this product is 10 to 15 days, with a full cure at 30 days. But as temperatures drop, the drying/curing process will slow significantly. Should your piece drop toward freezing temperatures while drying, the fats from the oils may get pushed out of the wood, compromising the finish.

Some finishes call for sanding between coats. One expert recommends keeping a sample finish board one step (and a full 24 hours) ahead of your showpiece. This way you not only can test the first coat of a finish, but you can test-sand it before applying the next coat. This sample board will act like a scout and will red-flag any number of issues with a finish drying improperly.

Storing your finishes.

Many finishes have a short shelf-life to begin with, and proper storage is important to preserving or extending that estimated shelf life. For oil finishes, the presence of oxygen in the can degrades the finish, so remember to cover up the can as soon as you’ve decanted what you plan to use. A technician at Sutherland Welles even recommends adding clean, smooth stones into the finish can, as a way to reduce the volume oxygen can fill. Some products can survive a freeze-thaw cycle, meaning they will still perform after you’ve let them freeze in your cold woodshop. Technically, solvent-based finishes will have a hard time freezing, but that doesn’t mean they should be stored in freezing temperatures. Room temperature is the gold standard for storing most finishes.

One tell-tale sign that a finish has gone bad is its smell. If a finish smells rancid, dispose of it properly. If the finish has separated or lost its consistency, you might try giving it a good stir. If it mixes up well, it might still be usable.

Until this point we’ve considered temperature as a factor, but humidity may also complicate matters. Take shellac, for example. In extremely high humidity, water vapor will pool under the shellac causing cloudiness. But at extremely low humidity, shellac may dry so quickly that it is hard to get a thin, even coat. Dreaming of French polish? Call your shellac distributor, and wait until temperature and humidity conditions are just as they prescribe.

On a cold winter’s day, I stayed home and called the manufacturers of the following finishes to get some answers about the way their products perform in the cold. This may be just a small sampling of the vast array of finishes on the market, but it paints a pretty clear picture. Cold-weather finisher, beware.

Recommended temperatures

Finish	Lowest Application Temperature	Ideal Storage	Freeze-Thaw Stable Oil-based finishes may not actually freeze
Osmo Polyx	50º–55ºF or 10º–12ºC	Room temp	Yes
Rubio Monocoat Oil Plus 2C	50ºF or 10ºC (60º–77ºF or 15º–24ºC preferred)	Room temp	Technically no (but if it mixes up well, it’s usable)
Sutherland Welles Polymerized Tung Oil	55ºF or 12ºC (65º–85ºF or 17º– 27ºC preferred)	Room temp	No
Murdoch’s Wiping Varnish	55º or 12ºC (65º–85ºF or 17º–27ºC preferred)	Room temp	No
Tried and True Danish Oil	Room temp preferred	“Not too finicky”	Yes
Genuine shellac w/ 190-proof denatured alcohol	50º–55ºF or 10º–12ºC	Room temp	Yes
Miniwax Polyurethane	50ºF or 10ºC (for 24 hours) (70º–85ºF or 20º–27ºC preferred)	Room temp	No
Miniwax Water-Based Polyurethane	50ºF or 10ºC (for 24 hours) (70º-85ºF or 20–27ºC preferred)	Room temp	No
Total Boat – Gleam SPAR Marine Varnish	50ºF or 10ºC (60ºF or 15ºC preferred)	Room temp	No
Real Milk Paint (paint)	50ºF or 10ºC and above	Unmixed powder— temperature irrelevant After mixed—refrigerator	Not after mixing
Real Milk Paint (tung oil)	50ºF or 10ºC	50º–75ºF or 10º–22ºC	No

 

The wood needs to acclimate, too.

Feeling a bit stymied by the cold? Here are a few tips and tricks you might consider. While wood is not a great conductor of heat, the surface temperature of the wood does matter. So even if you do not want to finish a piece of furniture inside your heated home, you might store it inside overnight before taking it out to finish. If you store products inside a garage, make sure to place them on an inside wall, closest to the house. And many woodworkers warm up their shops for finishing by creating a small “heat pen” with plastic sheeting and a small heat source. Others claim a simple space heater left safely near a drying piece in the basement may be just the ticket to a full cure. Be safe and take heart—spring is on the way!

 

Fine Woodworking Recommended Products

Zissner Seal Coat

Great as a sanding sealer, and as a final finish.

Waterlox Original

Versatile wiping varnish is easy to apply and great for both satin and gloss finishes.

Osmo Polyx-Oil

“If I had to choose one of these hard-wax oils to keep on hand, it would be Osmo Polyx-Oil. It’s relatively affordable and very easy to apply.” -Adam Godet