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Common Paint
Problems
Peeling of Interior Paint
Due To Moisture
Sources of interior moisture are condensation (windows &
sills), spills, leaking roofs, condensation from coldwater
pipes, or plumbing leaks (ceilings under bathrooms).
Initially, these sources of moisture will just cause
staining of painted surfaces, but if not corrected,
peeling results.
Peeling of Exterior Paint Due To Moisture
Moisture accumulating behind an exterior paint surface is
a common cause of adhesion failure. Poor caulking, lack of
vapour barrier in older homes, cracked siding boards,
plugged gutters and uncoated edges of planking on decks
are the most common entry points.
Once moisture gets into the surface, peeling paint soon
follows, particularly if the paint is a dark glossy
product exposed to direct sunlight.
Peeling Latex Paint From Surface Previously Painted
With Alkyd Paint
Reliable adhesion of latex paints to old alkyd surfaces
depends on:
The type of latex used in the product; 100% acrylics
generally have the best adhesion
The finish of the alkyd; flat alkyd is easily over-coated,
whereas gloss alkyd is not
The finish of the latex used; gloss and semi-gloss latex
paints have better adhesion to alkyd paint than eggshell
and flat
The amount of sanding done before painting; the old alkyd
surface must be properly de-glossed, not just scuff sanded
Whether all grease and soap residue has been properly
removed
Peeling Paint From Plaster Surface
Although drywall has replaced plaster in most home
construction, there are a lot of older buildings where
plaster still exists. The traditional primer for plaster
was an alkyd wall primer & sealer. When latex sealers came
onto the market, it was thought that they would perform
just as well as the alkyd. The problem has been that latex
tends to sit on the surface of the plaster where the
slower drying alkyd gave good penetration. If plaster was
over-trowelled (smooth & glossy) or powdery (poor mix)
latex sealers would only give marginal adhesion. Over
time, with additional coats of paint, the internal stress
of multiple coats exceeds the adhesion of the sealer to
the plaster and peeling results. If the area of paint that
is peeling is small, seal around the edges of the peeled
surface with orange shellac. This will prevent lifting of
the edge when the painting is done.
Peeling Paint On Garage Floors
In northern climates where snow is a reality of life four
months out of the year, it can be nearly impossible to
keep most floor paints from peeling off of concrete garage
floors. The problem is caused by the snow carried into the
garage on cars melting into pools of water. After a few
weeks, most latex, alkyd and polyurethane floor paints
will fail when exposed to such immersion-like conditions.
Have your garage floor acid-etched and then painted with
two coats of epoxy, the first coat reduced 20% for
penetration.
Varnish Peeling From Stained Surface
The use of solid hide & semi-transparent exterior stains
for hardwoods such as maple, birch or oak can cause
adhesion problems when used inside and then top-coated
with polyurethane varnishes. The problem is the lack of
penetration of the varnish allowed by the stained surface,
especially when using multiple coats of stain or an
excessively heavy application to create a dark finish. The
result is a heavily pigmented film, which is not very
strong and can fail under the stress of 3 or 4 coats of
varnish. When failure occurs, there is usually stain
residue on the back of the varnish chip.
Alkyd Paints That Dry Too Slow
There are a number of things that slow down the drying
time of alkyd paints:
Cool temperatures generally below 10-15ºC
Humidity above 70%
Lack of ventilation
Too much colorant in the paint
Paint applied too heavily
Alkyd Paints That Dry Too Fast
If alkyd paints are drying to fast, the causes are
usually:
Using dark colours in direct sunlight
Exposure to too much wind thereby causing the solvent to
evaporate too quickly
Surface is too hot
Thinning with a solvent that is too fast for the
application conditions; the "open time" of alkyds can be
increased by using Penetrol or a slow solvent such as
turpentine. Maximum addition is 10-15%.
Yellowing of Alkyd Paints
Alkyd paints will yellow with time. The degree of
yellowing is normally quite slow, but in the absence of
light (surfaces behind pictures or furniture set against
walls) the yellowing can be quite severe. Ammonia based
cleaners can also cause rapid yellowing of alkyds. There
can also sometimes be enough ammonia in latex paint to
cause yellowing of alkyds. When using both alkyd and latex
to paint a room, use latex first, followed by the alkyd to
reduce the chance of yellowing. Although alkyd paints can
be used in severe temperatures of up to 200ºF, some
yellowing of lighter colours can occur well below that
temperature.
Bleeding From Knots in Wood
Soft woods, such as pine, contain excessive amounts of sap
that can bleed through paint films. Although aluminium
paint is excellent for holding back sap, adhesion of most
paints to aluminium paint is poor, so it should not be
used for this purpose. Sap streaks and knots in the wood
must both be painted with orange shellac or speciality
sealers prior to painting. This type of bleeding can be
quite persistent, and additional treatments of sealer may
be required after the finish coats have aged. |
