Spraying in cold weather without losing ratio

Cold is mostly a temperature-management problem, not a chemistry one. Keep drums conditioned before the truck moves, not after you arrive. A-side and B-side that sit at different temperatures is the most common cause of off-ratio foam in winter.

Watch hose temperature at the gun rather than the machine display, and give the primary heaters time to recover between passes. Check the substrate too: spraying warm foam onto a cold deck traps condensation and costs you adhesion. If the substrate is below the manufacturer’s minimum, warm it or wait.

Precondition the drums, not just the truck

A heated box on the truck keeps drums from freezing overnight, but it doesn’t mean the chemical inside is actually at spray temperature. Dense 55-gallon drums take longer to come up to temperature than the air around them. Build in real soak time — several hours at a minimum — rather than judging by how warm the drum feels on the outside.

Watch pressure as closely as temperature

Cold thickens both components, and a proportioner working to push cold, viscous material through the hose will often show a pressure imbalance before the ratio actually drifts. If you see the pressures on A and B start to separate, that’s your early warning — don’t wait for the foam itself to tell you.

Substrate temperature matters as much as air temperature

Job-site air temperature is easy to check and easy to get wrong as your only reference. Steel, concrete, and OSB all hold cold long after the surrounding air has warmed up, especially early in the day or in shaded areas. Use an infrared thermometer on the actual surface you’re about to spray, not the ambient reading on your phone.

A quick pre-shot checklist for cold weather

• Drums soaked at temperature for several hours, not just stored in a heated box
• Hose heat confirmed at the gun, not just at the machine display
• Substrate temperature checked directly, above the chemical manufacturer’s minimum
• A and B pressures matched before you pull the trigger on the first pass
• A test shot on scrap material if conditions are marginal

None of this replaces the chemical manufacturer’s cold-weather data sheet — always spray to their published minimums. But most winter ratio problems come from skipping one of the steps above, not from a mystery in the chemistry.