Why is Climatic Testing Important?
The monitoring of the climatic conditions during the whole coating process is of critical importance to ensure that the resulting quality and performance of the coating is at an optimum. Key climatic parameters include:
- Surface temperature (Ts) – the temperature of the surface
- Air temperature (Ta) – the temperature of the air
- Relative humidity (RH) - how much humidity is present in the air, compared to how much there could be - expressed as a percentage
- Dewpoint (Td) - the temperature at which moisture in the air will condense on a surface
- Delta T (TΔ) - the difference between the dewpoint temperature and the surface temperature of the substrate to be painted
- Wet bulb temperature (Twb) - the temperature a volume of air would have if it were cooled to saturation (100% relative humidity) by the evaporation of water into it, with the latent heat being supplied by the volume of air
- Dry bulb temperature (Tdb) - the temperature that is usually thought of as air temperature
- Wind speed – the rate at which air is moving in a particular area
- Surface moisture – the moisture content of a substrate
If the climatic conditions are wrong at the time of application, then the coating may fail - regardless of the other vital parameters. Additionally, the temperature at which the coating is stored can also be important. Temperature can affect the shelf life, viscosity and application characteristics.
Monitoring the climatic conditions as the coating cures (dries) is also important. Coatings which cure too quickly can crack. In freezing conditions the coating can freeze, changing the structure of the coating. If the drying time is extended, due to the temperature being too low, then there may be delays in applying further coats which could bring more surface defects.
Furthermore, it is important to measure climatic parameters before, during and after surface preparation – particularly when blasting. This is a requirement of many standards, including IMO’s Performance Standard for Protective Coatings on Salt Water Ballast Tanks. Climatic parameters are also required to be assessed in the powder & industrial coatings industries.
What is Dewpoint?
Moisture on the surface during the application process leads to adhesion problems with the coating.
Measuring Temperature, Relative Humidity & Dewpoint
Relative humidity and dewpoint are calculated from other connected parameters.
Measuring Wind Speed
If the coating is being applied by spray, then we want to ensure all the paint exiting the spray gun lands on the surface being coated
Oven Temperature Profiling
If the coating being applied is a powder coating, then a specific temperature is required for a specified period during curing.
The presence of moisture within a material will result in poor adhesion, premature coating failure and poor appearance.