Effects
of Painting under the wrong conditions
The environmental conditions (e.g., temperature, humidity) present
during the application of any paint can have a profound effect
on the paint’s ultimate performance. This statement is true
for both waterborne acrylic coatings as well as solventborne coatings
such as oil-based alkyds. For waterborne acrylics, how the environmental
conditions affect the film formation process will determine their
impact on final properties.
Manufacturers usually recommend both temperature
and humidity ranges for proper application of their waterborne
coatings. If used outside these ranges, problems such as cracked
films or less than optimum performance may occur. Some possible
scenarios are:
Humidity is too high:
Manufacturers usually recommend a maximum humidity of 85 –
90%. When the application humidity is too high, coalescing co-solvents
can leave the wet paint film before water. When water finally
evaporates, there is not enough coalescent to soften the latex
particles and allow them to deform. Air movement can help alleviate
this potential problem.
Temperature is too
low:
Manufacturers usually recommend a temperature range of about
45 – 100° F for application of waterborne acrylic
coatings. If the application temperature is too low, the latex
particles will not fuse together completely. In the worst case,
this can result in a cracked or powdery film. A cold surface
temperature of the structure being painted can also lead to
this condition, as the temperature of a thin film of wet paint
is quickly affected by the substrate temperature. Thus, the
applicator should pay attention to both air temperature and
surface temperature when applying waterborne coatings. Surface
temperatures should also be at least 5° above the dew point
to prevent condensation on the surface.
Temperature is too high:
If application temperature is too high, water and co-solvents
can flash off before the latex particles have an opportunity
to coalesce. Surfaces can also reach very high surface temperatures
due to either sunlight or service conditions (e.g., steam piping),
and also must be taken into account.
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