The subject of painting sheet-metal roofs is one of great importance,
says the _Builder, Decorator and Wood-Worker_, not only on account of the
protection afforded, but because the material, when properly colored, can
be made pleasant to the eye when placed in exposed positions. While many
kinds of paint have been discovered and patented, composed of a great
variety of materials, it is a question if there is a substance used that
is an effective substitute for linseed oil, regarding the effectiveness
of which an authority on the subject says: “By consulting experienced
and unbiased painters you will learn the fact that there is no vehicle
pigments at all approaching linseed oil in effectiveness and durability,
especially for exposure to the weather. A good paint must be both hard
and elastic. It requires hardness to prevent abrasion and wear, and
elasticity to prevent cracking from expansion and contraction. Nothing
but linseed oil will give these qualities, for, strange as it may seem to
many in these days of novelties, the pigments really add but very little
to the effectiveness of paints. Mark, we say the best of pigments, for
many pigments are the reverse of protective, and are really destructive
to both the vehicles and the material which they are supposed to protect.
For example, coal tar and all its products, whether called dead oil,
asphalt, rubber, etc., are of the class just described, and their use at
any price, especially for covering sheet-metals, is a wanton waste of
money. Extended experiments have demonstrated that there is no better
pigment for metal than a good iron ore ground to an impalpable powder. To
be most thoroughly effective the pigment must be intimately incorporated
with the vehicle, which can best be done only by grinding them together
in a stone mill by steam power.” It is of the greatest importance that
sheet-metal roofs, especially those made of iron, should be protected
from the action of the elements, as when so protected there is hardly
any limit to the time they will last. In order that the paint should be
effective, it should be applied before the iron has had an opportunity
to rust, and the first coat should be of the best quality and applied
in the best manner; or if it is defective it is plain that it will not
only require repainting far sooner than it should, but no matter how
good the subsequent coatings of paint are, they cannot be effective if
founded on an original coating which has commenced to crack or peel, as
it certainly will if not prepared with the best methods and materials.
Another important point to be observed in the painting of sheet-metal is
that the paint should not be too thick, as it is the linseed oil that is
to be depended on to furnish protection, and as the action of the air on
the surface of the exposed oil gives it a particularly hard surface, two
thin coats of paint are much more durable than one thick one.
Remember, it is the =rust-preventing= qualities of linseed oil, combined
with the oxide of iron, that makes steel or iron sheets resist the
corrosive action of oxygen, which is ever present in the atmosphere. (See
page 101.)