Summer Finishing Tips
With the temperatures increasing here in Southern Arizona, it's time to shift gears and dial in best practices for summer time finishing.
Heat is very challenging to cope with when you need to execute a flawless, orange-peel free finish, but there are steps you can take to mitigate some of the issues that come with summer spraying.
- The most obvious step, start early! Temperatures are always the lowest of the day an hour or so before sunrise. If you're working in a space that is adequately lit, you can work smarter and faster by starting at 4am or so. Yeah, getting up that early is no fun, but neither is the time and money wasted sanding down a whole project that had a less than desirable final finish because it was sprayed at noon.
- Your next step is to know and understand how to use the various lacquer additives and retarders available. Various solvents have different evaporation rates, and using the appropriate blends can really help with the leveling of your final topcoat when the temperatures are approaching 100°. 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, and it works in a wide variety of solvent based coatings. Use no more than 10% per gallon to start, 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 above 90°. 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, 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.
- Acetone - While not a retarder, acetone is the most commonly used chemical in wood finishes. It's evaporation ratio of 5.8 is very high, which tells you why lower VOC coatings (550 VOC and especially 275 VOC) can be challenging to work with in warm temperatures.
- When you are thinning and retarding your coating for summer 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.
- Avoid the sun at all costs. Shops with south, east or west facing doors or windows will receive significantly more sun than a building with north facing openings. Direct sun can increase surface temperatures of your material considerably faster than ambient air temp will. Work around the sun's position throughout the day and do your best to stay out of the light.
- Try to keep freshly sprayed pieces away from moving air of any kind. Whether it be a fan blowing or an intake fan sucking, drawing air across the surface can skin the coating over and prevent your additives from having enough time to do their job.
Keeping these precautions and tips in mind can help you prepare for the challenges of summertime spraying.