Drying of polyurethane coatings, including water based products, is influenced by:
- Film Thickness
The recommended ambient environment for applying 1 pack moisture curing polyurethanes, 2 pack polyurethanes and water based polyurethanes is between approximately 12-30° C and 40-80% relative humidity. Optimum application conditions are approximately 25° C and 60% relative humidity. It is not recommended to apply polyurethane coatings if the ambient climatic conditions fall outside these boundaries.
A drop in temperature slows down curing of the applied polyurethane coating. The temperature of a floor may be significantly lower than the surrounding air temperature. The temperature of the coating material itself can be extremely low if it is stored in a van overnight.
The following problems may be caused by applying the coating at too low a temperature:
- Drying and curing is affected. Tack free time and recoat time is longer than in optimal conditions. Catalyst may be added to increase curing rate, but do not exceed the mixing ratio specified by the manufacturer.
- A slower drying time may also increase the amount of dust that will adhere to the floor during drying.
- Moisture may condense on the floor due to the lower temperature of the floorboards. This can react unfavourably with the coating.
- Satin and matt finishes are very sensitive to temperature extremes. Temperature variations on the floor (such as hot spots due to sunlight) can create gloss variations.
On cold days, avoid applying the coating early in the morning or late in the afternoon.
Polyurethane coatings should not be applied on cool, damp days.
Drying of water based coatings is significantly slower on humid, cold days.
Uncontrolled airflow must be avoided. Increasing airflow will reduce the drying time but it will also increase the risk of surface defects including bubbling and dust or dirt contamination.
Film thickness should be within the range specified by the coating manufacturer.
Reference: Toby Technical Bulletin TB017