Troubleshooting Guide - Dusting on Limewash

Limewash - Dusting

1. Lack of moisture control - Drying and carbonation are two different processes, just because a limewash is dry it does not follow that it has carbonated. Drying is just the process of moisture leaving the limewash, whereas carbonation is the absorption of Co2 from the atmosphere and this is how the limewash gains its strength. In carbonation of lime can only take place in the presence of water. If limewash dries before sufficient carbonation has taken place then dusting can occur. Therefore the suction of water from each successive coat of the limewash must be controlled by wetting down the background beforehand, then regular misting with water and protection from the wind and the sun are crucial in tempering this process.
2. Inadequate protection from direct sunlight/wind – please refer to point 1) above.
3. Exposure to freezing temperatures – causing expansion of the water within the limewash. Limewash should not be applied in temperatures below 5°C or if they are likely to fall below that before it has had a chance to carbonate.

 Resolution 

All dusty limewash needs to be removed; this can either be done with a stiff brush or if large areas are affected this can be done carefully with a pressure washer. Limewash can then be reapplied following manufacturers guidelines.