When applying coatings, the most important factors to consider
are the condition of the substrate, the surface temperature, and the
atmospheric conditions at the time of painting.
Paint application should only be carried out when good atmospheric
conditions and clement weather prevail.
Painting should not be carried out :
• when the air temperature falls below the lower drying or curing limit of
the coating,
• during fog or mist conditions or when rain or snow is imminent,
• when the surface to be painted is wet with condensation or when
condensation can occur during the initial drying period of the paint.
During the night steel temperatures fall. They rise again during the day
but there is always a lag in movement of steel temperature compared to
the atmospheric condition, so condensation on the steel surface is
possible. Condensation will occur if the steel temperature is below the
dew point of the atmosphere.
BORDERLINE CONDITIONS:
Relative humidity itself rarely creates a problem. Most paints will tolerate
high humidities, but humidity should not be permitted to lead to
condensation on the surface being painted. In order to determine
whether or not a surface is wet, the steel temperature should be
measured using a surface temperature thermometer and the dew point
calculated after measurement of humidity with a hygrometer. Paint
application should not take place when steel temperature is less than 3°C
(5°F) above the dew point.
Paint should not be applied when surfaces are affected by rain or ice.
Some two component paints (for example certain epoxy coatings) should
not be applied at low temperatures as curing may be retarded.
EXTREME CONDITIONS :
LOWER TEMPERATURE EXTREME:-
Generally, extreme conditions refers to ambient temperatures below 5°C
(41°F) or above 40°C (104°F).
Below 5°C (41°F) the curing of coatings, such as traditional two
component epoxies, slows down dramatically and for some paints curing
stops altogether. International Paint’s product range contains certain
epoxy and polyurethane coatings specifically formulated for use at
temperatures below 5°C. Consult International Paint. Other marine
coatings are not so severely affected; chlorinated rubbers and vinyls are
quite suitable for use at temperatures below 0°C (32°F) provided that the
surface is clean and free from ice or frost.
HIGHER TEMPERATURE EXTREME:-
At the other extreme of 40°C (104°F) and above, the drying and curing of
paints is rather rapid and care should be taken to avoid dry spray. This is
caused by the too rapid loss of solvent from paint droplets between the
spray nozzle and the surface. It can be avoided by:-
(i) Keeping the spray gun at the minimum suitable distance from the
work piece, spraying consistently at 90° to the surface being
painted.
(ii) Adding thinners, if necessary, up to a maximum of 5% by volume.
In conditions of high temperature, techniques must be adopted to prevent
defects such as voids, pinholes, bubbles and poor coverage due to the
over rapid evaporation of solvent. However, provided that good standards
of workmanship are maintained, it is normally possible to satisfactorily
apply most International Marine Coatings products on to steel substrates
up to 65°C (149°F). Consult International Paint for specific product
guidance.
