Painting in cold weather (i.e. temperatures below 50°F or 10°C) presents multiple problems and can be particularly problematic for tradesmen when decorating unheated premises prior to occupation.
Slower application and drying times
Low temperatures affect both the application and drying of paint. Alkyd and oil paints, based on natural oils and resins, become more viscous in lower temperatures and require thinners to be added. Some paints are, however, manufactured with special additives to overcome this problem and improve their performance. Emulsion paints at low temperatures suffer from slower evaporation rates of their water content and volatile additives. To dry they need 4 hours at around 75°F (24°C) before a recoat can be applied or 6 hours at 10°C. Painting in cold temperatures using alkyd paints will need even longer and in some cases over 48 hours before a recoat can be applied.
It’s also important to be aware that the actual surface temperature can vary between different areas on the same structure, especially when temperatures are low and/or volatile, causing the drying time to be unpredictable and with potentially uneven results. (This is very evident on metal surfaces compared to wood)
Varnishes are vulnerable to blushing and a dull gloss finish when used in cool and/or damp conditions. Fast evaporating solvents commonly found in varnishes can cause the surface to cool, sometimes just enough to drop below the dew point so causing condensation to form on the surface and leading to blushing.
Some common problems that can be encountered when decorating in cold temperatures include:
- Inadequate ventilation so allowing the build-up of solvent and/or water vapour levels that are damaging to both the final finish and also the health of the operative;
- Surface cracking and improper film formation causing a powdery effect;
- Either resistance to successfully carrying out any touch up work or touch up work looking different to the non-touched up part(s);
- Poor stain resistance;
- Uneven colour;
- Water spotting (especially with emulsion/water-based paints);
How to avoid cold weather problems
If you've no choice but to paint in cold temperatures, check the manufacturer’s guidelines for this for best practices.
If possible, heat the room and maintain a constant ambient temperature but avoid using open flame gas heating as this produces moisture and will raise the humidity significantly; dry heat from electric or radiant heat is always the best option.
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