Winter Finishing Tips
Now that we are looking at another few months of cooler temperatures, we thought we'd do another installment of best practices and winter time finishing tips. Given that Phoenix weather can shift almost 80° from summer highs to winter lows, there are some unique challenges to wood finishing during these months of milder temperatures and increased moisture.
- While starting early is optimal in the summer, in the winter, that is obviously not the case. With humidity at its highest and temps at their lowest, spraying before 7AM from November through March is very difficult, since wood coatings are best sprayed at temps around 80°. If you're able to shift your finishing production to after 10AM, when the temperature is generally above 60°, you'll find it is much easier to avoid orange peel, and possible blushing, in your finish.
- Coatings storage and handling are vital during the winter time. Wood coatings become much more viscous under 80°, as they are not able to flow properly after atomization at the gun. How can you avoid these issues? Simply setting pails on 2x4s will insulate them from colder ground temperatures. Storing in a warmer room of your shop will help even more. Using pail warmers is also an option, however, it is extremely important to use a timer, adjust the temperature precisely and never leave them unattended when attached to a pail. Keeping your coatings warmer will ultimately lower their viscosity and allow them to perform as expected.
- HEAT! Having a warmer environment in your shop is extremely beneficial when finishing in the winter. However, as most guys don't have central heating in their facility, you'll have to be creative in order to achieve the best finish. We strongly discourage using any type of catalyst propane heater (the "jet engine" models come to mind) when working with solvent based coatings. Recipe for disaster. Start by opening south-, east-, and westward facing doors as soon as the sun hits so you can get some much needed heat into your shop. The best solution is using shortwave infrared heating lamps during cold mornings. These shortwave lamps are derived from the more intense longwave lamps used to cure automotive finishes. The shortwave lamps are safer to use around lower temperature, single component wood coatings that tend to bubble and wrinkle under higher temperatures. Using a lamp on your surface before spraying is a great way to start, and putting the lamp over the material after application will cure the coating faster while also helping to level more effectively.
- Just as solvent additives can correct the issues we see during the summer, the are also important for solving problems in the winter. With colder temperatures, we are looking for additives that decrease viscosity while also allowing the lacquer to flow better after being sprayed. These additives also increase the time before the coating "skins" over and will help prevent orange peel from appearing in our final finish. The lower the evaporation ratio number (the closer to 0, the better), the slower the solvent evaporates from the coating, giving a longer open time for improved leveling. Adding any of the following solvents, aside from Acetone, will change the VOC of your coating. Check local regulations to ensure you will remain compliant.
- Butyl Acetate - When we're talking about evaporation rate, this is the standard of which all other solvents are measured. With a rate of 1.00, Butyl Acetate is a very versatile solvent that is recommended as a reducer for most environmental conditions. There's little danger if it is over-used (don't go crazy!), and it works in a wide variety of solvent based coatings. Use no more than 10% per gallon, we say start with 5% then add from there.
- Methy Amyl Ketone (M.A.K.) - Not to be confused with MEK (which is an accelerator, not a retarder), M.A.K. is a great solvent with a distinct smell that offers substantially slower evaporation than Butyl Acetate. Rated at 0.5, M.A.K. should be your go-to when spraying below 70°, and is just as effective as it when spraying in summer time temps. M.A.K. will keep the coating open longer, while allowing to flow much better before it dries. We recommend no more than 5% per gallon to start, pushing up to 10% in seriously challenging conditions. Our testing has shown that adding greater volumes of M.A.K. can leave you with a softer top coat.
- Glycol Ether - Along with the less commonly available Diacetone Alcohol, this is the slowest solvent available. Sometimes sold under the brand name "Butyl-Cellosolve". With an evaporation rate of 0.18, this is significantly slower to leave the coating than even M.A.K. If you absolutely need to spray when triple digit temps are looming, this can help extend your open time as long as it possibly can be. Glycol ether really excels in eliminating "blushing" in humid conditions (usually over 60%), as it allows moisture trapped in the coating when it's sprayed to evaporate before the coating "skins" over and seals it in. Great care must be taken not to over-use glycol ether, as adding too much can result in a permanently soft final finish. We recommend no more than 5% per gallon for the most extreme conditions.
- Correct small areas of orange peel or blushing by first trying an aerosol retarder, like No-Blush or Super Blush from Mohawk. A light mist of these products may be enough to reanimate the lacquer, correcting the problem without your finisher having to respray the entire piece.
- When you are thinning and retarding your coating for winter spraying, keep in mind that you are also altering the solids content and sheen. Over-reducing can leave you with a shinier finish, as you are displacing the flatting paste which gives you the lower sheen spec'd on the label of the can. Also, thinning in general, while necessary, is a money-loser. While it makes lacquer easier to spray, thinners and retarders are expensive, and they are not part of the coating as they will completely evaporate when the film is dry. Use discretion when reducing because it's literally making your money evaporate!
- One more tip about thinning. It can be beneficial to keep a journal of different blends of retarders and thinners for specific dates, times, temperatures and conditions. One season of note taking can really help you going forward. Type up your guide, laminate it and stick it in your spray booth. Having a "quarterback wristband" to refer to when environmental conditions are challenging can save a ton of time and effort when you're prepping your coatings for spraying.
Keeping these precautions and tips in mind can help you prepare for the challenges of summertime spraying. Enjoy these tolerable temperatures while you can!