Spring serves as a transitional season between winter and summer, featuring the most drastic weather fluctuations and frequent temperature ups and downs throughout the year. For construction workers engaged in large-scale exterior wall projects, strong winds in northern regions and high humidity in southern areas make the volatile climate quite troublesome.
In northern China, alternating north and south winds prevail with high wind speeds. Strong winds bring cold air, lower temperatures and reduce air humidity.
In southern China, continuous drizzles occur frequently with alternating cold and warm weather. Abundant rainy days lead to high relative humidity, easily causing dew formation and moisture regain.
Such conditions inevitably give rise to various troublesome problems during spring exterior wall construction.
Causes of Uneven Color and Whitening Phenomenon
- Under drastic temperature differences, dry powder putty fails to dry sufficiently. A large amount of alkaline substances will be produced after cement hydration reaction inside it.
- The high alkali content of the putty layer will cause poor film formation when applying exterior wall flat coatings and texture coatings. The coating cannot dry and form a protective film normally in a short time, thus prolonging the film-forming period.
- Excessively long or failed film formation weakens the encapsulation effect of emulsion on powder, sand and pigments.
- Frequent early spring rains keep the wall surface soaked for a long time. During water migration, vertical rain streaks appear on the paint surface, eventually leading to uneven color and whitening of the coating film.
How to Avoid Such Problems During Construction
- In northern regions where the minimum temperature ranges from 5℃ to 10℃, conduct coating construction preferably from 10 a.m. to 4 p.m. Especially for primers and water-based topcoats with high resin glass transition temperature (Tg), construction at excessively low temperatures will cause paint film cracking.
- Keep a close eye on weather changes and suspend construction on rainy days. Test the moisture content of the base surface after rainfall, and resume coating construction only after reaching the standard to prevent paint film blistering.
- Regularly measure the surface temperature of the base and ambient relative humidity. Stop construction when the base surface temperature is below 5℃ or the relative humidity exceeds 85%.
- Take effective shielding measures in case of rain during the base surface drying period.
- Protect finished and semi-finished products properly. Apply necessary covering protection during rainy or dusty weather.
- Water-based coatings dry and form films slowly under high ambient humidity, so properly extend the recoating interval. It is recommended to recoat thin-layer coatings every other day, and thick coatings with an interval of more than two days.
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