Causes:
Blistering is caused by vapor that expands between the
surface and the paint film. Sometimes, excessive moisture
saturates wood siding or condenses on it due to humidity,
construction defects, or lack of effective vapor barriers.
As this moisture evaporates, lower humidity and high
temperature generate pressures within the wood and on the
adhesive bond of the coating. Fresh blisters fill with
water.
As the surface dries, water
evaporates, but the paint film does not recover.
Solvent-based coatings are most susceptible to blistering.
A common cause of blistering is solvent entrapment, or
painting with solvent-based coatings in direct sunlight on
a too-warm surface. Due to their higher absorption of
heat, darker colours tend to blister more than light ones.
Thicker application or recoating prior to complete cure of
a previous coat can also cause blistering. Under this
condition, the paint surface dries before all the solvent
is released from the underlying film.
Solution:
If the blistering is caused by moisture, repair loose
caulking and install vents or exhaust fans.
For homes with lap siding, install siding vents. Vents or
fans allow moisture from inside to evaporate before
penetrating wood siding. This will minimize future
blistering problems.
To repair the surface, sand and scrape peeling paint to
bare wood.
Prime exposed areas and repaint.
If large areas of paint have blistered and need to be
removed, high-pressure washing or a heat gun will speed
the process.
Heat blisters develop in freshly-applied coatings only.
When broken, they don't contain liquid and are not
associated with a surface defect that requires repair.
Remove these blisters by scraping and sanding. Recoat the
surface under more favorable conditions. |
