As the temperatures start to drop. Its time to start thinking about the problems that can occur when applying polyurethanes. There are two main classes of polyurethanes:
- Aliphatic (Low {non} Yellowing)
- Aromatic (Yellow with Time)
Non-yellowing formulations are much more sensitive to ambient conditions of temperature and humidity than the yellowing types, with much slower curing of the non-yellowing in colder weather.
Problems that can occur in cold weather (below 15ºC)
1.Viscosity of the coating increasing as the temperature decreases can result in:
- Reduced Flow with potential for ‘orange peel’, track marks’, etc.
- De-aeration reduced due to air bubbles finding it harder to rise to the surface in a viscous medium
- ‘Quilting’ effect (non-levelling over adjoining timber pieces) increases, especially with parquetry
2. Curing is slower particularly with True NON-YELLOWING solvent based coatings. Slow curing symptoms due to cold weather can include ‘balling’ when sanding or foot imprints can be seen the following day.
3. Solvent evaporation is slower with the following being possible;
- ‘Pimples’ or ‘nibs’ from dust due to wet surface being ‘open’ for a longer time
- Extraction of soluable species (e.g. waxes) from some timbers e.g. Brushbox, coupled with condensing of heavier solvent fractions in cool, moist air, can create a ‘haze’ or ‘oil film’ on the surface.
Trouble Shooting Guide for Cold Weather
| PROBLEM | REASON | CAUSE | REMEDY |
| Poor Flow | Cold floor and/or cold air temperature and/or cold material Viscosity in can has increased with time | Viscosity higher with lower temperature Past shelf life or hot storage – never use products that have expired past their use by date! | Add up too 30ml per litre (3%) Wet Edge Extender 3320 Wet Edge Extender may not work if material has reacted too much in can |
| Orange Peel | Cold floor, air or material Film to thick | Viscosity high | Add Wet Edge Extender 3320 Minimise film thickness |
| Low Gloss | Low temperature/dew point reached Possible if dew is on grass outside | Dew point if reached can deposit microscopic moisture particles on surface causing dulling effect | Apply finish in warmer part of day |
| Slow Drying | Cold (and maybe dry) conditions | Aliphatic have slow cure in cold conditions | Add DURAPOL 5995 Accelerator if compatible |
Please Contact your Polycure Technical/Sales Representative for further information.