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THE INSTITUTE OF INDUSTRIAL RESEARCH


  Allerton S. Cushman, A. M., Ph. D., _Director, In Charge
       Division Metallurgical Problems_.

  Henry A. Gardner, _Assistant Director, In Charge Division of
       Paint Technology_.

  N. Monroe Hopkins, Ph. D., _In Charge Division of Electrical
       Engineering and Electrochemistry_.

  Chas. A. Crampton, M. D., Ph. G., _In Charge Division of
       Food and Drug Products_.

  G. W. Coggeshall, Ph. D., _In Charge Division of Mill
       Problems_.

  Chas. Baskerville, Ph. D., F. C. S., _In Charge Technology
       of the Rarer Elements_.


Copyright, 1911, The Institute of Industrial Research




                 THE INSTITUTE OF INDUSTRIAL RESEARCH


                           THE PRESERVATION

                                OF THE

                     EXTERIOR OF WOODEN BUILDINGS


                                  BY

                ALLERTON S. CUSHMAN, Director
                 THE INSTITUTE OF INDUSTRIAL RESEARCH

                                  AND

               HENRY A. GARDNER, Asst. Director
                      IN CHARGE DIVISION OF PAINT
           TECHNOLOGY, THE INSTITUTE OF INDUSTRIAL RESEARCH


                            [Illustration]


                            WASHINGTON 1911



  WASHINGTON, D. C.
  PRESS OF JUDD & DETWEILER, INC.
  1911





PREFACE.


For a number of years the writers have been making a study of
industrial problems and have been publishing the information which they
have acquired, regarding the value of various structural materials,
for the benefit of consumers as well as producers. The Institute
of Industrial Research has received so many requests recently for
information in regard to just what paints should be selected for the
protection and decoration of houses and other buildings that it has
seemed best to sum up the subject in the form of a special pamphlet
or bulletin. It is only after years of investigation work carried on
by the authors, both separately and in co-operation, that any review
of the work has seemed possible, for only recently have the results
of tests carried on in a number of different localities seemed to
justify a definite opinion in regard to the best selection of exterior
paints. No attack on any one paint material is here included, but the
value of each has been carefully weighed, and the attempt is made
to discuss them in the light of experience and knowledge. It is the
authors' intention in this bulletin to put into the hands of architects
and paint users who may not be thoroughly familiar with the technical
properties of paint materials, information which will enable them to
make a proper and intelligent selection of paints for the preservation
and decoration of the exterior of wooden buildings.




The Preservation of the Exterior of Wooden Buildings


_Lumber and its Relation to Paints_: The proper choice and treatment of
lumber is one of the most important problems which the builder as well
as the painter has to face. When about to build a dwelling, barn, or
other structure made principally of wood, the question is sure to arise
in regard to what variety to select so as to get the maximum service
and money value. The locality in which the structure is to be built
must often have a bearing upon this question. While it is true that the
painting of each type of wood demands the special consideration of the
painter, it is also true that the study of paints for wood protection
points toward the production of a paint that will give satisfactory
results under all conditions and on all grades. It is the writers'
opinion that a paint may be made that will be perfectly well suited
for the preservation of every species of wood, provided the paint is
properly treated in the hands of the skillful and intelligent painter,
who can produce lasting results on almost every type by varying the
proportion of thinners and oil in the various coats. The painter who
uses the same paint on soft pine, and again on hard pine, without
making a special study of how to reduce the priming coat for the hard
pine, will be likely to get inferior results on the latter. In case
of failure, the natural impulse is often to place the blame upon the
paint, whereas the real responsibility may rest upon the painter's lack
of knowledge.

  Note.--For a more detailed account of the lumber question,
       see "Modern Lumber as a Problem for the Painter," read by
       John Dewar, at the Convention of Master House Painters' and
       Decorators' Association of Pennsylvania, January, 1911,
       Pittsburg, Pa.


  Photographs Showing Different Forms of
  Decay Exhibited by Improperly
  Made Paints

[Illustration: Blistering]

[Illustration: Chalking]

[Illustration: Checking]

[Illustration: Cracking]

[Illustration: Scaling]

[Illustration: General Disintegration]

_Signs of Paint Failure_: Those who are responsible for the care and
maintenance of property are familiar with the condition of surface
presented by almost all wooden buildings or structures which have been
improperly painted with inferior paints. "Chalking" or "flouring"
are terms used to describe the condition of a paint surface which
has deteriorated within the paint film. The formation of minute
fissures, generally spoken of as "checking," as well as the effects
best described as cracking, scaling, peeling, and blistering, are
other signs of failure which cause paint coatings to present an
unsightly appearance, and which point inevitably either to the use of
improperly made paints or to improper application. The cause of these
conditions is not difficult to understand when even a brief study of
the character of the materials entering into the composition of a paint
has been made. It is, however, a fortunate circumstance that the proper
admixture of different types of pigments enables us to correct the
strong tendency exhibited by special pigments to rapidly deteriorate
in an oil film. This point will be more fully discussed in a later
paragraph.


_Requisites of a Good Paint_: Progressive manufacturers are aiming to
produce a paint which will show, under the widest range of conditions,
good hiding power, adhesiveness, freedom from internal strains,
permanency of color, relatively high imperviousness to moisture,
sufficient elasticity to prevent scaling or cracking when subjected
to expansion or contraction, and freedom from the chemical action
which results in deep checking or excessive chalking. Such a product
as this cannot be attained, in the writers' opinion, by the use of
any one pigment in linseed oil. In order to meet all the demands as
stated above, there should be in an economical and durable paint a
proper percentage of the various pigments which, united, will tend to
correct each other's faults, and thus produce a durable paint coating
of maximum efficiency.


_The Composition of Paints_: As is well known, a paint is a mixture of
one or more pigments and a vehicle which acts the part of the spreading
and binding medium. Up to the present time the vehicle portion of
paints has generally been made of linseed oil, admixed with some
volatile thinner, such as turpentine. The subject of oils and paint
vehicles will be discussed more fully later on.


_Physical Properties of Pigments_: The pigment portion of a paint
for use on barns and farm buildings may, if desired, be composed
of properly selected iron oxides or other colored pigments, even
containing in some cases a moderately high percentage of silica, clay,
or other inert materials, and give perfectly satisfactory results. For
the preservation and decoration of dwellings, however, the pigment
portion of paints is generally made as a whole or in part of the more
expensive white pigments, such as white lead and zinc oxide. The
relative values and properties of these white base pigments will now be
taken up.


_White Leads_: White lead, either of the corroded or sublimed type, is
perhaps the most generally used of all the white pigments as a paint
base. Corroded white lead is a basic carbonate of lead, while sublimed
white lead is a basic sulphate of the same metal. Both of these types
are white, and admirably adapted as painting materials. They take
relatively the same amount of oil and spread easily, producing paint
films which are highly opaque and which, therefore, hide efficiently
the surface upon which they are placed. Sublimed white lead is a
relatively finer pigment than corroded white lead, and seems to show
a tendency to chalk to a greater extent upon exposure to the weather.
Corroded white lead is more alkaline, however, than sublimed white
lead, and when used alone with linseed oil generally shows a tendency
to chalk to a considerable extent in a short time and to show deep
checking, thus permitting the admission of moisture. The alkaline
nature of this pigment produces considerable action upon certain
tinting colors and results in fading or darkening, when mixed with
delicate greens or blues.

The use of white lead has been condemned in some parts of this country
as well as abroad, because of its alleged poisonous properties. While
it is true that lead poisoning may occasionally occur in some factories
where the workman and his conditions are not properly safeguarded, it
is, nevertheless, a fact that lead poisoning very seldom occurs among
painters of experience and cleanly habits. Carelessness in mixing
white lead is, fortunately, a practice almost obsolete among modern
painters. The use of paints already ground in oil by means of machinery
to a pasty condition, allowing easy working and reducing, obviates the
danger of lead poisoning from any such cause as this, even though the
percentage of lead in such paints is in preponderance. Recent efforts
that have been made by the legislatures of certain States to brand
lead paints as poisonous are not only unnecessary, but show a complete
ignorance of the problem.


_Zinc Pigments_: Another pigment which has proved itself of great
value to the painter is zinc oxide. The use of this pigment may be
said to have almost revolutionized the paint industry of the world,
and its increased consumption during the last ten years is sufficient
evidence of its value as a painting material. Zinc oxide is produced
by oxidation and sublimation of zinc ores and is not only extremely
fine, but of great whiteness. It has good hiding power, although not
quite so great as that shown by the white leads. It tends to produce
a glossy surface, making it especially valuable for use on interior
work and in enamels. When used alone it has the effect of hardening
the oil film in which it is enveloped, and upon long exposure causes
cracking and scaling. However, when the sublimed or corroded white
leads are properly combined with zinc oxide, a more durable surface is
produced, the shortcomings of each pigment being overbalanced by the
good properties of the other. The proper combining properties of zinc
oxide with white lead may be said to vary between 20 to 55 per cent
of zinc oxide for paints designed for exterior use. In the opinion of
the authors, lead and zinc pigments in the above percentage, properly
blended and ground, make paints of far better wearing value than can be
produced with either white lead or zinc oxide used alone.


_Zinc Lead_: Zinc lead, a pigment sublimed from mixed lead and zinc
ores and containing about equal proportions of zinc oxide and lead
sulphate intimately combined, as well as leaded zinc, a produce
similarly produced, but with the zinc oxide running about 75 per cent,
are white base pigments of value, which are used to a considerable
extent. They are generally slightly off color, however, and are
therefore used most largely in paints which are to be tinted in various
colors.


_Lithopone_: Lithopone, a pigment produced by precipitation, and
consisting of zinc sulphide and barium sulphate, is of great value in
the manufacture of interior paints. On account of its liability to
darken and disintegrate, however, it is seldom used on exterior work,
although recent tests have shown that when used in combination with
zinc oxide and whiting, it gives very promising results.


_Crystalline Pigments and Their Use_: Barytes (barium sulphate), silex
(silica), whiting (calcium carbonate), gypsum (calcium sulphate),
asbestine (silicate of magnesia), and China clay (silicate of
alumina) are white crystalline pigments which, when ground in oil,
become transparent. All of these pigments possess the property of
strengthening a paint film made of white lead and zinc oxide, and often
increase the durability of such a paint. Barytes, silica, and China
clay are especially valuable for this purpose. Asbestine, because of
its needle-like structure and low gravity, prevents settling and acts
as a reinforcer of paint films. Whiting or calcium carbonate should be
used when zinc oxide is in excess in a paint, so that the hardness of
the paint may be overcome.

A white paint must be possessed of sufficient opacity to efficiently
hide the surface upon which it is placed, when three coats are applied
for new work or two coats for repainting work. Mixtures of the white
leads and zinc oxide, with the latter pigment running not over 55 per
cent, will easily produce such a result and wear well. It is generally
deemed advisable, however, by most manufacturers to take advantage of
the excessive opacity of such mixtures, which allows the introduction
of moderate percentages of those inert pigments which give greater
strength and other desirable features to a paint. The percentage of
natural crystalline inert pigments to add to a white paint made of
lead and zinc must, however, be moderate and insufficient to detract
materially from the hiding power of the paint.

  Note.--Pigments such as silica, barytes, China clay, and
       asbestine are thoroughly inert. Recent investigations have
       proved that they accelerate the drying of linseed oil, but
       this is not due to any chemical action they exert, but rather
       to their physical action in distributing the mass of oil in
       which they are ground, and thus allowing a greater surface to be
       exposed to the oxygen of the air.

       It is also possible that some of the inert pigments may stimulate
       oxidation by catalytic or contact action, although they are not
       chemically active in themselves.


_White-Paint Formulas_: From these conclusions which have come
from wide experience in the testing of paints under actual service
conditions, there can be recommended to the buyer of paints and to the
manufacturer and master painter those machine-mixed paints in white,
made by reputable manufacturers, the composition of which will show a
mixture of white lead and zinc oxide, with the latter pigment within
limits of between 15 to 55 per cent, and especially the same mixtures
reinforced with the moderate percentage of crystalline inert pigments
referred to above.

Tinted paints possess greater hiding power than white paints, and
the above proportions would be somewhat changed for a tinted paint
containing any percentage of coloring material. Tinted paints are,
moreover, far more serviceable than white paints, as will be shown
later.


_Mill vs. Paddle_: The mixtures under consideration should be ground
in linseed oil by the manufacturer, through stone or steel mills, to
a very fine condition, as it is only through proper grinding that the
pigments can be properly blended. The mixing of paint by hand is,
fortunately, to a large extent a thing of the past. The uneven lumping
of hand-mixed paints are often the cause of their failure. Such ancient
and crude practice should be avoided by every painter, for it is more
economical to obtain semi-paste paints, properly ground by machinery,
to such a condition that they may be easily broken up and tempered.
Such paints may be reduced to the proper consistency with oil and
volatile thinner for application to any kind of wood.

In the opinion of the writers, a majority of the paints sold by
reputable dealers and made by reputable manufacturers in this country
are not only made from the best linseed oil and highest-grade pigments
obtainable, but are put up in a form ready for the painter to thin down
with full oil or turpentine reductions, either for priming work or to
be used without reductions for finishing coats. The large metropolitan
painter who wishes to make his own tints and shades may, however,
prefer to have his mixed pigment paint ground by the manufacturer in
heavy paste form for certain purposes.


_Results of Field Tests_: A careful analysis of the results of field
tests which have been carried on in different parts of the country
would be far too voluminous for insertion in this bulletin. The
official findings of special committees of inspection have already been
published in special reports. Whereas there may still remain ground
for some difference of opinion in regard to the interpretation of the
results obtained on the various test fences, there can be no doubt that
considerable information of the highest value has been yielded, both
to the producers and consumers of paints. One of the principal results
obtained from these tests has led to the opinion expressed above by the
writers, that better results can be obtained by a proper mixture of
selected pigments than by the use of any one pigment in linseed oil.
This conclusion has also been reached by engineers of the United States
Navy, and, as a result, the specifications of the Bureau of Yards and
Docks for paints made of straight white lead and oil have recently been
changed to call for white lead combined with upwards of 50 per cent
of zinc oxide. Many engineers and master painters have interpreted the
results of the tests in the same way, and the attention of the authors
has been called to a number of opinions which show that the tendency
of demand among those who are properly informed is for a high-grade
combination type of paint rather than for any single pigment paint.


_Color_: The selection of the color for a dwelling or other structure
is a matter that depends largely upon the good judgment and taste of
the owner, combined with the advice of the painter. One point, however,
should be impressed upon the mind of both, namely, that PRACTICALLY
ALL SHADES OR TINTS MADE UPON A GOOD WHITE PAINT BASE, THROUGH THE USE
OF PERMANENT TINTING COLORS, WILL BETTER WITHSTAND EXPOSURE TO THE
ATMOSPHERE THAN THE WHITE BASE USED ALONE. Owing to the cheerful
effect produced by the use of white paint on dwellings, a very large
quantity of white will continue to be used. If these white paints are
designed in line with the suggestions brought out above--that is to
say, if the white lead bases are properly reinforced with zinc oxide
and other pigmentary materials--better results will undoubtedly be
obtained, as far as appearance and durability is concerned, than if
white lead had been used alone. The consumer should remember, however,
that more durable results will be obtained by the use of tinted paints.


_Reductions and Thinners_: Turpentine, with its sweet odor, high
solvent action, and wonderful oxidizing value, has always taken first
place among the volatile liquids used for thinning paints. Wood
turpentines, produced from the steam distillation of fine-cut fat
pinewood or from the destructive distillation of stumpage and sawdust,
have been refined in some cases, by elimination of odor and toxic
effects, to such purity that they are equally as good as the purest
grades of gum turpentine, and their use is bound to increase in the
paint industry.

The painter and manufacturer have come to understand that certain
grades of asphaltum and paraffine distillates are equally as
satisfactory as turpentine for use in paints for exterior purposes.
Those volatile oils which are distilled from crude oil with either
a paraffine or asphaltum base and possessed of boiling point, flash
point, color, and evaporative value approximating similar constants of
turpentine, are excellently suited to partly, and in some cases wholly,
replace turpentine in exterior paints. A little additional drier added
to paints thinned with these materials will cause oxidation to take
place in the proper time.

       *       *       *       *       *

Prominent master painters[A] have shown that benzol, a product obtained
from the distillation of coal tar, differing from benzine, a product
obtained from the distillation of petroleum, is a valuable thinner to
use in the reduction of paints for the priming of resinous lumber such
as cypress and yellow pitch pine. The penetrating and solvent value of
benzol is high, and it often furnishes a unison between paint and wood
that is a prime foundation to subsequent coatings, preventing the usual
scaling and sap exudations, which often appear on a painted surface.
Because of the great solvent action of benzol, however, this material
should never be used in the second and third coatings. These facts will
doubtless interest the Southern painter, who has so much wood of a
refractory nature to paint.

[A] Dewar, Titzel _et al._


_Oils_: The increasing cost of linseed oil has raised the interesting
question as to whether or not it is good practice to use an admixture
of other oils in connection with it, in high grade paint coatings.
Strong differences of opinion will probably be found in regard to this
question, and undoubtedly further investigation work is necessary in
order to decide it. A number of different oils have been proposed for
the purpose, of which, perhaps, soya bean oil is the one which has been
most prominently discussed. No definite formulas, however, should be
recommended until the results of investigations which are now being
carried on are in hand. A systematic series of test panels is now
being erected in Washington, D. C., on the grounds of The Institute of
Industrial Research, which are designed to gather data covering just
this point.

The flax crop conditions have been most discouraging during the past
two years, and the natural shortage of seed has caused a rise in the
price of linseed oil, which has necessitated a rise in the price
of paint. The added protection to be secured, however, through the
frequent application of paint far outweighs any increased cost which
has been caused by the rise in price of the raw commodities entering
into the composition of paint.

       *       *       *       *       *