Wicked cold out there this week, and the shop doors are shut….. The heater's humming, the dory's on the strongback, and I'm about to wipe her down with acetone before the next coat of epoxy. That's exactly when a winter shop turns on you. In July the big doors are open and the air takes care of itself. In November everything you put in the air stays in the air, right there with you and that heater.
Why it matters: A closed-up shop is a box. Solvent and epoxy vapor build up in it. WEST SYSTEM says plainly that vapors can build up in unvented spaces, and they want ample ventilation or an organic vapor respirator. Acetone, the stuff we all wipe with, has a flash point of 0°F per NIOSH. Its vapor is heavier than air and can travel along the floor to a flame across the room. Then there's the heater itself. An unvented kerosene or propane torpedo heater puts carbon monoxide into the room, and it adds moisture and CO2 too. Those feed amine blush on your fresh epoxy. So the same heater can light the vapor, gas you, and wreck your coat. Let's fix all three.
Materials
- Disposable nitrile gloves (neoprene, butyl or natural rubber also work per WEST). Plenty of them
- NIOSH-approved organic vapor (OV) cartridges, black label. If you'll be sanding too, use combination OV/P100 cartridges, black and magenta (3M 60921 is one)
- A zip-top bag or sealed container for the respirator between uses
- Foil-backed rigid foam insulation, tape, and a light bulb or heating pad for a warm box
- Your solvents, with the lids kept on
Tools
- A window or box fan you can set in a window blowing out
- A half-face respirator that fits your face
- A battery-operated CO alarm
- A thermometer in the shop, and one in the warm box
- For heat while the epoxy cures: an electric heater with a thermostat and a tip-over shutoff
Steps
- Heat the shop first, then shut the flame heater off. Bring the shop, the boat and your materials up to temperature with whatever you've got. Then, before any thinner, acetone or solvent finish comes out, turn off every heater with an open flame or a glowing element and let it cool. Jeff Jewitt makes the same point in Fine Woodworking: stoves and heaters with an open flame or glowing element are a hazard around flammable finishes. Propane construction heater makers agree. One DESA manual says to keep the area clear of gasoline, paint thinner and other flammable vapors.
- Set up cross-ventilation, not a stir fan. Put the fan in a window near the work, blowing out. Crack a window or door on the far side for make-up air. Then stand so the fresh air comes past you first, across the work, and out the fan. A fan in the middle of a closed shop just stirs the vapor around and into your face. Jewitt's rule for hand-applied finishes is a fan rated in cfm about equal to the room's volume (length x width x height). A 16 x 24 shop with 8 ft ceilings is 3,072 cubic feet, so look for about 3,100 cfm. He's clear that it only works if you give the replacement air a way in, and that it isn't enough for spraying.
- Put on your gloves and respirator, and check the seal. Every time you put the respirator on, do the negative-pressure check from OSHA's appendix. Palms over the cartridges, breathe in gently so the mask pulls in, and hold it ten seconds. If it stays pulled in with no leak, you're sealed. Then do the positive check: cover the exhalation valve and breathe out gently. You should feel a little pressure and no air leaking at the edges. Skin is the bigger exposure with epoxy, though. WEST says skin contact is the most common way people get exposed to resin and hardener, and sensitization can come after many exposures or just one. Glenn House, Gougeon's product safety director, says a typical 4 to 6 mil disposable lasts about 30 minutes with epoxy, so change them before then, and double-glove on long jobs.
- Wipe or brush, then purge. Do the solvent wipe or the epoxy coat. Keep lids on the cans and get solvent rags out of the shop. Let the fan run until the smell is gone. Then close up and heat again. That's Jewitt's winter routine too: apply, vent, then close up and reheat for drying.
- Keep the epoxy warm instead of the whole shop. Build a box from foil-backed rigid insulation with a light bulb or heating pad inside. WEST says to keep resin and hardener at 70°F to 90°F that way. Warm epoxy pumps and mixes better and wets out better. Warm the joint itself with a heat lamp or hair dryer, or tent just that area. Know your hardener's floor. WEST 205 Fast cures down to 40°F (4°C), but slowly. 206 Slow and 207 Special Clear shouldn't be used below 60°F (16°C), and 209 Extra Slow not below 70°F (21°C). As a rule, cure time doubles for every 18°F (10C) drop.
- Heat for the cure without combustion in the room. If you need heat while the epoxy cures, WEST says to avoid unvented open-flame heaters that burn kerosene or fuel oil. Unburned fuel can contaminate the surface, and the extra moisture and CO2 contribute to amine blush. Turn up the thermostat, or use electric heaters or electric blankets. CPSC says an electric heater should have a thermostat and a tip-over shutoff, and to avoid ordinary extension cords. If you do run a combustion heater at other times, follow its fresh-air rule. That DESA manual calls for at least a 3 square foot opening to outside air for each 100,000 Btu/hr.
- Change cartridges on a schedule and store them sealed. 3M says to write the date on the cartridges when you open them, change them on a schedule, and change them right away if you can smell or taste the solvent. Between uses, store the respirator and cartridges in a sealed bag or container, away from the vapor. Even sealed, vapor can migrate through a used cartridge overnight. 3M says that for chemicals boiling below 65°C, an OV cartridge shouldn't be used longer than one shift. Acetone boils at 133°F, which is 56C. So after an acetone day, those cartridges are done.
- Hang a CO alarm in the shop. CPSC says unvented fuel-burning heaters pose the greatest CO threat, and mild CO symptoms like drowsiness, headaches or nausea are often misdiagnosed. A battery CO alarm is cheap. CPSC says to test alarms monthly and replace the batteries every year.
MOAM's shop note: The mistake I see most is the guy who opens a window "for ventilation" and leaves the torpedo heater roaring right next to the boat while he wipes her down with acetone. That's the worst of everything: an ignition source, CO, and a blush factory, all in one corner. Here's the trick. Do your solvent work first thing, right after you've warmed the place up and shut the heater off. The shop holds its heat long enough for a wipe-down. Then purge, close up, and let the epoxy cure under electric heat or in a tent. And never clean epoxy off your hands with solvent. WEST says not to. Use a waterless skin cleanser, then soap and warm water.
MOAM Out.
Sources: WEST SYSTEM: Preventing Overexposure WEST SYSTEM: Epoxy Safety (PDF) · Epoxyworks: Cold Weather Bonding · Epoxyworks: Let's Talk About Amine Blush · Epoxyworks: Disposable Gloves · Fine Woodworking: The Finishing Environment (Jeff Jewitt) NIOSH Pocket Guide: Acetone · ICSC 0087: Acetone · NIOSH cartridge color chart (CDPR) · 3M 60921 OV/P100 cartridge 3M: Reuse of Organic Vapor Cartridges · 3M Respirator FAQs · OSHA 29 CFR 1910.134 (Appendix B-1 seal checks) · CPSC: Space Heater Safety · CPSC: CO Alarms · CPSC: Kerosene Heater Safety · DESA propane forced-air heater manual














