Evening star., 1934-11-24
A|R-COND|T|0N|NC
AFFECTSPA|N
Special Primers Necessary
to Protect Exterior
From Moisture.

tect exterior paint from moisture in
air-conditioned homes, Henry A.
Gardener, president Of H. A. Gardner
Laboratories, Inc, Washington, says
in Industrial and Engineering Chem
istry, publication of the American
Chemical Society.
Use of porous primer, or first coat,
prevents peeling, blistering and other
defects caused by vapor forced through
the walls from the interior, he finds.
A light pearl gray tint which absorbs
ultraviolet light extends the efficiency
and life of special primers, his investi-
cations disclose.
Dwellings of the future will to a
great extent be provided with air.
conditioning and humidifying Sys-
tems," Mr.. Gardner points out. "It is
easy to visualize the large amounts OF
moisture which could be forced
through the siding of house during
the Winter months, because of the
continuous relatively high vapor
pressure existing within the house.
Peeling Due to Water.
"Peeling of the paint will then be
observed, since peeling is due almost
entirely to the passage of water from
the back through the siding, where it
finally strikes the paint coating and
causes blisterS and other defects. 1t
is evident, therefore, that the primer
paint to be used on the siding OF air
conditioned dwellings should be OF a
relatively porous character rather
than non-porous.
For instance, the application OF
metal powders dispersed in spar var
nish to produce an extremely moisture
resistent printing film may not be
good practice. 1t might cause many
cases of peeling which otherwise would
not occur. 1t is apparent tnat the
printing system for such dwellings,
should be of such a nature as TO allow
the passage of moisture from the IN
terror of the dwelling through the
siding and through the film. Such a
film should have a valve-like action
and resist the passage of any suostan-
tial amount of water from without.
IF objection is raised that such ac-
ton, while ideal, is impossible, the TACT
remains that the results are the same.
External moisture usually is applied
in large doses, rain, for short periods
Internal moisture is applied in small
doses, vapor, for long periods. The
time element is vastly more 1mpor-
tant than the intensity element.
THE type of primer paint suitable
for use on refractory species of wood
is one which embodies linseed oil as
the liquid, rather than spar varnish,
since a dried film of linseed oil is
more porous to moisture than dried
film of varnish. An adnlixture Of pig
ments might preferably be employed
in such primers.
Diatomaceous Earth Urged.
'eIt is good practice to use in the
pigment portion about 10 per cent OF
diatomaceouS earth, or similar porous
inerts, which have the peculiar prop
erty of forming with linseed oil, in the
presence of other pigments, a film
which is quite porous to the moisture
that comes through siding.
Printing paints made of heavily
pigmented white lead-linseed oil COM
position, and containing in the pig
ment portion about 10 per cent of
diatomaceous earth, as well as per-
centages of zinc and titanium pig
ments, have given excellent results.
The final film formed by such lin
seed oil paints produces surface upon
which subsequently applied coats of
linseed oil paint will properly adhere,
whereas proper adherence is not al
ways observed when finishing coats of
oil paint are applied to powdered me-
tallic pigment-varnish primers.
The tinting of special primers to a
light pearl gray seems to extend their
efficiency and life. Apparently ultra
violet light penetrates white paint
made with certain pigments and af-
fects the Oil after long exposure, while
dark-colored pigments in a paint alb
Sorb ultraviolet light and prevent it
from destroying the oil, thus making a
more permanently elastic film.
Small percentages of graphite, car
bon black. lampblack or aluminium
powder may be used for this purpose
The color thus developed is not suf-
flciently dark to cause any difficulty
in obscuring the surface with two
subsequent coats of white paint"
Better Wood Helps Paint.
1t IS important that the builder
realize the advantage of using edge
grain siding, as such surfaces hold
paint much better than f1at-grain
boards. according to Mr.. Gardner
The higher the grade of lumber and
the fewer the knots, the greater will
be the success of the painting job
he says.
The use of special primers is to be
recommended for Douglas fir, Nor
way pine and Southern yellow pine
referred to by painters as refractory
woods" he adds.
Since a greater number of dwell
ings in the future must be cCsl-
structed of Southern yellow pine
Norway pine and Douglas fir, because
of the preponderance of these woods
it is important that methods be de-
vised to give the greatest possible
satisfaction with exterior paints.
"On many woods, such as cedar
cypress, redwood and white pine, il
Is not necessary to use special prim-
ing paints, provided the surfaces are
fairly dry. and satisfactory iobs NAV