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Class III: Exterior Surface Conditions Generally Requiring Total
If surface conditions are such that the majority of paint will
have to be removed prior to repainting, it is suggested that a
small sample of intact paint be left in an inconspicuous area
either by covering the area with a metal plate, or by marking
the area and identifying it in some way. (When repainting does
take place, the sample should not be painted over). This will
enable future investigators to have a record of the building's
Cause of Condition
Peeling to bare wood is most often caused by excess interior
or exterior moisture that collects behind the paint
film, thus impairing adhesion. Generally beginning as blisters,
cracking and peeling occur as moisture causes the wood to
swell, breaking the adhesion of the bottom layer.
There is no sense in repainting before dealing with the
moisture problems because new paint will simply fail. Therefore,
the first step in treating peeling is to locate and remove
the source or sources of the moisture, not only because moisture
will jeopardize the protective coating of paint but because,
if left unattended, it can ultimately cause permanent damage
to the wood.
Excess interior moisture should be removed from the building
through installation of exhaust fans and vents. Exterior
moisture should be eliminated by correcting the following
conditions prior to repainting: faulty flashing; leaking
gutters; defective roof shingles; cracks and holes in
siding and trim; deteriorated caulking in joints and seams;
and shrubbery growing too close to painted wood.
After the moisture problems have been solved, the wood must
be permitted to dry out thoroughly. The damaged paint can
then be scraped off with a putty knife, hand or mechanically
sanded, primed, and repainted.
Cause of Condition
Cracking and alligatoring are advanced stages of crazing.
Once the bond between layers has been broken due to intercoat
paint failure, exterior moisture is able to penetrate the
surface cracks, causing the wood to swell and deeper cracking
to take place.
This process continues until cracking, which forms parallel
to grain, extends to bare wood. Ultimately, the cracking becomes
an overall pattern of horizontal and vertical breaks in the
paint layers that looks like reptile skin; hence, "alligatoring."
In advanced stages of cracking and alligatoring, the surfaces
will also flake badly.
If cracking and alligatoring are present only in the top
layers they can probably be scraped, hand or mechanically
sanded to the next sound layer, then repainted. However, if
cracking and/or alligatoring have progressed to bare wood
and the paint has begun to flake, it will need to be totally
removed. Methods include scraping or paint removal with the
electric heat plate, electric heat gun, or chemical strippers,
depending on the particular area involved. Bare wood should
be primed within 48 hours then repainted.