How Do You Heat a Great Falls Shop for a Winter Epoxy Install?

September 16, 2026

An unheated Great Falls garage or shop will not hold a 50 degree slab on its own in January. Temporary heat can open the window, but only if it is the right kind of heat, started early enough and left running long enough.

The Slab Sets the Schedule, Not the Air

Most epoxy systems want a surface roughly in the 50 to 85 degrees F range, held above the dew point, with the product data sheet as the final word. The mistake that ruins cold-season floors is treating the thermometer on the wall as the measurement that matters. Air in a closed shop can be brought up twenty degrees in an hour. A four inch slab on frozen ground cannot.

The gap between those numbers is wide in a Great Falls winter. Normal highs at Great Falls International Airport fall to 43.7 degrees F in November, 35.6 in December and 35.3 in January, and freezing nights run 22.6, 27.0 and 26.9 across those months, with 20.7 nights a year at or below 0 degrees F. The ground under an attached garage carries that cold into the concrete and holds it, so an infrared thermometer read on the slab itself, in several spots including along the overhead door, is the only number worth scheduling around. A thermal mass that size also takes time to move, which means heat switched on the morning of the install arrives too late.

What Temporary Heat Actually Has to Do

A heater in the corner is not a plan. Holding a slab inside the product window through a cold-season install is a set of specific requirements, and missing any one of them shows up in the finished floor:

• Run heat 24 to 48 hours ahead of prep so the concrete comes up, not just the air above it
• Hold that temperature through grinding, mixing, application and the full stated cure period
• Keep the surface above the dew point the entire time, which is a separate problem from keeping it warm
• Use indirect-fired equipment with the burner outside and clean air ducted in, or electric radiant heat
• Tent off the bay being coated and seal the overhead door perimeter
• Keep any heater from blowing across a wet film, because a hot spot flashes the surface unevenly

Direct-Fired Propane Is the Common Mistake

The unvented propane salamander that lives in most shops is exactly the wrong tool here. Burning propane or kerosene indoors without a flue produces water vapor and carbon dioxide and releases both into the room, which is fine for thawing a workbench and bad for a curing floor.

Two things go wrong. The vapor condenses on a slab still colder than the air, putting moisture between the concrete and the coating at the moment adhesion is being established. The carbon dioxide reacts with the amine curing agents in epoxy at the surface, leaving a greasy or cloudy film that stays tacky and interferes with the next coat. Indirect-fired heaters keep combustion and exhaust outside and duct only warm dry air in; electric radiant units avoid combustion entirely, at the cost of the power to run them.

Dew Point, Condensation and Chinook Swings

The standard requirement on a coating data sheet is that the surface sits at least 5 degrees F above the dew point and is rising rather than falling. In a heated shop in January that is usually easy. During a chinook it is not.

A warm wind can move surface temperatures dramatically in a matter of hours here, and the air arriving with it carries moisture. Push that air into a building over a slab still cold from the previous week and the floor sweats, sometimes visibly and sometimes not. Read slab temperature and dew point together, and postpone rather than chase a warm afternoon. How this climate drives coating decisions is covered in the chinook country concrete guide.

Prep and Moisture Testing Do Not Get Easier in the Cold

Conditioning the space is a prerequisite for testing it. Both common moisture tests are run at service conditions, meaning the building has to sit at its normal operating temperature and humidity before the numbers mean anything. ASTM F1869 measures moisture vapor emission in pounds per 1,000 square feet per 24 hours, with a limit commonly near 3 pounds, and ASTM F2170 uses in-situ relative humidity probes against limits usually set at 75 to 80 percent.

Mechanical prep is unchanged by the season. ICRI Technical Guideline 310.2R sets the concrete surface profile scale from CSP 1 to CSP 10, with diamond grinding typically landing at CSP 1-3 and shot blasting at CSP 3-7, and the profile a system needs does not relax because it is December. What does change is dust and containment inside a tented, heated space, covered under concrete grinding and surface prep.

When to Change Products, and When to Wait for Spring

Chemistry can take some load off the heaters. Polyaspartic systems cure at lower temperatures than standard epoxy and widen the cold end of the usable range, which is part of why they show up so often on garage floor coating work in this climate. They do not remove the dew point requirement, but they shorten the window that has to be held.

A heated commercial building is a different calculation, because the space is already conditioned and the constraint is downtime rather than temperature. That is the usual path for commercial epoxy flooring scheduled in winter.

Sometimes waiting is the right call. An unheated detached shop with no power for radiant heat is a spring job, and saying so early beats a floor that delaminates by March. Temporary heat, tenting and a longer schedule are real cost drivers, which the cost page covers, and the climate figures sit on the by the numbers page. Anyone weighing a winter slot against spring can start with how cold-season floor coating work is handled in Great Falls.

More from the blog

• How Do You Seal Exterior Concrete in Great Falls Before Winter?
• When Is the Best Time to Epoxy a Garage Floor in Great Falls?
• Why Do Epoxy Floors Fail in Great Falls? Five Local Causes