Treating wood for protection and service


Material Information

Treating wood for protection and service
Physical Description:
Mixed Material
Hunt, George M ( George McMonies ), b. 1884
United States -- Forest Service
Forest Products Laboratory (U.S.)
University of Wisconsin
U.S. Dept. of Agriculture, Forest Service, Forest Products Laboratory ( Madison, Wis )
Publication Date:

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Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 29347783
oclc - 756503209
System ID:

Full Text


Septlembcr 1938


," o.' -. \

Madison, Wisconsin
In Cooperation with the University of Wisconsin

( 4 R~ctvit

1,1741 3



GECRGE M. HUNT, Principal Chemist

Wood, as a raw material, generally requires less special treatment to
fit it for service than most other raw materials. But a certain degree of
preparation to enhance its qualities and prolong its usefulness is essential.
This has long been recognized. The practice of painting wood, for example,
arose before the dawn of history; likewise the gluing of wood, and the
pitchingn" of ships planking.

In the modern era, there is double reason for carrying on such practices
with care and skill. Not only is an exacting public to be served, but for
every failure in woods performance, technology is ready to press the claims
of other materials that will meet requirements more closely, if not more
cheaply. The service life of wood must be better safeguarded against both
natural enemies and man-made hazards. Processes by which wood is prepared
for special types of use must be developed and improved. In all this the
active aid of research is needed. Investigations of the mian.y kinds of treat-
ments and applications required fall for the most part into four well defined
fields: Preservative treatment; painting and finishing; fire-protective
treatments; and gluing and related processes.

Decay, the greatest destroyer of timber in use, is ably assisted by
insects and marine boring organisms. Thorough preservative treatment and
proper precautions in construction are needed to thwart these harmful agen-
cies. The degree of success attained in treatments gives wood today a strong
position as an economical material for railway ties, poles, pilinr, and other
outdoor timbering. Without such protection the movement toward concrete and
metal for all kinds of structures subject to decay and insect dwr.C.j;c would
be greatly accelerated. There is still need for great improvement in prr-
servatives and preservative methods, in order to increase their effectiveness,
reduce the cost of wood per year of service, and make treated wood more
generally available.

Various degrees of treatment are involved, depending upon the intended
use-the heaviest treatments, with creosote, being required for piling in
teredo-infested waters. Vast quantities of wood are wasted through insuf-
ficient penetration. Investigations of the effect of temperature and pressure

Pushed in Journal of Forestry, September 193
-Published in Journal of Forestry, September 19138.


in a thoro.ihgoing series of experimental treatments have shown ho' to gain
bettor penetration by usirig moderate pressures with relatively high t'..cratures,
thus obtaining higher mobility of the preservative liquid. As an iir. ort nt
outgrowth of the temperature studies, new heat-conduction formulas for wood
have been derived, placing the preheating stage of the preservative proc,-" on
a basis of accurate control for the first time and removing it from the costly
cmpiricir,, of the past.

A constant stream of new preservatives, of varying degrees of excel-
lence, s..1- outlets among the consuming public. Some of these are offered for
use by standard pressurce-impr-gnit ion methods. Most, however, are recormeended
for surface or "brush" treatments. Despite mr-r,, attempts to devise a quick
test for iud:in preservative efficiency, the old method of service records,
even though time-con..ui.inL, remains the only reliable one. Some 50,000 test
specimens in great variety of size, character, treatment, and geo-r.-l".cal
placcrr.Lfit, arc at present under observation for the compilation of such records
on a great number of preservatives, Meanwhile studies of the chemical prin-
ciples of toxicity and tests with many species of wood-destroying fun.i are
laying groundwork for the development of new preservatives as a scientific
undertaking, rather than a promotional coup.

The one timber item most in need of pres..r-.tive treatment tod-y is
farm fence posts, of which the number replaced each year by reason of decay
is in the neighborhood of 400 million. Effective home treating methods
hitherto offered have not found wide acceptance, and commercial treoatiments
are beyond the reach of the majority of farmers. The most promising recent
development in simplifying and chclipenflLif. fence post treatment is an adapta-
tion of the Boucherie process, by which green, round, unped.led posts of low
decay-resistance can be made as durable as cedar at a cash outlay of 5 to 10
cents per post. The treating chemical is zinc chloride and the means of
applic tion is a used tire-tube stretched over the end of the post. The
advant. ;us of the method are obvious. Experiments with posts of a number of
species ar, under way, and results thus far encourage the hope that post
treatments by the tire-tube method may soon become common practice.

Red will no lon--er be the dominant color note of the American barn of
the future, if research disclos.-ires in regard to paint durability make their
full impact. 2.posere tests made thro-.ghout the country have proved th'.t on
all commerrcial lumber species the longest service and best all-around pro-
tection against weathering is rendered by paint in which the pigment is
flake alujjiinum. The silvery luster of such paint will probably work -gainst
its acceptance for the complete painting of houses, but as a priri:-.- coat
its use will often prove of distinct advantage .

This finding is one result of a broad investigation of wood painting,
having as its practical objective a reduction of the consumers paint bill,
which now amounts to some half a billion dollars a year. Causes of paint
blistering, cracking, peeling, and discoloration have been annllyzed, means
of avoiding abnormally early paint failures pointed out, and the paint-
holding characteristics of different woods determined. It is in respect to


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its lasting quality on the more difficult tyye of woods that aluminum paint
has been found outstanding.

The role of moisture in walls as an enemy of paint has been discovered,
accounting as it does for many paint troubles. The remedy in such cases lies
not with the paint but with effective means to prevent moisture accumulation--
although pure white lead is more resistant to moisture blistering than mixed
pigments. An unsuspected factor of incompatibility has been found to lie in
the chemical make-up of different paint pigments, so that certain sequences
of coatings in repainting are now known to be safe, and others doomed to fail-
ure. Even for the owner who is deliberately neglectful of repainting, research
gives information of value, for a coating of white lead or, in some climates,
white lead and zinc oxide, is found to retain some of its appearance value
long after its other surfacing qualities have given out.

It is believed that a revolutionary inprovcrYc'nt in painting practice
and paint purchasing can be brought about by a system of paint classification
and graJing roughly analogous to lumber grading and species selection. With
this objective in view, a tentative system has been devised and is now being
urged upon a reluctant industry for improvement and adoption. Ready-mixed-
paint formulas are constantly changing and varying over a wide range in
character and quality. The purchaser is generally at a loss to tell good
paint from poor. Specific recommendations for the use of mixed-pigment pre-
pared paints are almost impossible as long as the present confusion is
allowed to continue, and a major effort on the part of paint technologists
is needed to remedy this situation.

VWood is by nature a combustible substance, and efforts to make it
"fireproof" in the sense that brick and stone are fireproof arc beside the
mark. Objectives in this regard must be confined to reducing fire hazards in
construction and treating wood with materials that will reduce the speed of
burning and check the spread of flame. By such means the danger of fire from
causes both internal and external to the house can be held to a practical
minimum, so that no just grievance can be brought against wood except for
situations of extreme fire risk.

Of 150 chemical compounds and mixtures thus far tested as imp rc --ting
materials, those involving ammonium phosphate, ammonium sulphate, borax, and
boric acid were found best. All require high absorptions of chemical for
their full effect, and for that reason cannot be considered cheap. Resistance
to decay, insects, and leaching can be combined with fire resistance, but
these advantages, too, are gained at considerable cost. In the course of the
investigations a yardstick cf the effectiveness of a treatment was devised
and has since been widely adopted, both in the United States and abroad. T i.'Ls
is the fire-tube test, by which the loss of weight of a standard specimen is
measured during the actual course of combustion,

M.'iny fires originate from ci-arette butts,burning match stems, and
other sources. To prevent fires growing from such beginning-s is half of the
battle in reducing fire losses. Coatings that can be applied to the surface



with brash or spray -un, in contrast to ii.pregnation treatments, offer pronmie
in retarding the spread of fire. While no coatir:.- c'r. yet bo recommended for
gencrail use, research in this field is being actively prosecuted in the hope
of developing a coatin,. or coati!.'s that can be used effectively and economi-
c:lly to prevent rapid spread of fire in walls and basements, and can be
tpylied by the home owner in old or new structures.

In general estimation, plywood would never rate as a "fireproof" ma-
terial. Yet it has been found that if the new phenolic resin glues arc used
in the making, a considerable factor of fire resistance is obtained--far more
than when animal, casein, or vegetable glues are used. Plywood panels 1.7
inches thick, glued with phenolic resin adhesive and exposed to flame accord-
ing to underwriters' standards, resisted burning through for a whole hou-ar.

The constant improvement of glues *rnd gluing is a vital part of wood
utilization research. Glue for centuries has been a stout companion to wood
in meeting difficult requirements of fabrication. By contributing to smooth-
ness and str'", th of joining, it has multiplied the serviceability of wood in
the hands of the craftsman. As new demands devolve on wood, the demands on
glue become all the more urgent. Better gluing gives better plywood for more
exacting uses. Control of gluing technique makes for dependable veneered
products and supplies the average home with better, stronger, and more attrac-
tive furniture. Water-resistant glues make possible built-up and laminrted
construction broad new fields of service--in building, in transportation, in
aeronautics. To an unpredictable der, the future of wood lies with scien-
tific developments in gluing.

The Laboratoryts first major studies in this field resulted in the dis-
covery of bcsic principles of good gluing with starch, animal, casein, and
blood glues--findings which for the first time made gluing a sound technology
instead of the mysterious rule-of-thumb practice it had been for ages. Other
results were determination of the gluing properties of more than 40 species
of wood, the development of new and better low-cost casein and blood glues,
and the formulation of the first reliable methods for testing the strength,
water resistance, and durability of glue joints. Hot-press resin glues of
outstanding moisture resistance are now available in increasing numbers, and
studies arc proceeding in the special techniques involved in their use. Soec
of these glues are found to retain a large percentage of their original strength
over several years of severe exposure to alternate wetting and drying. Their
perf)rmarce in this respect is far superior to that of any of the older types.
An economical cols-prms glue having the high strength and water resistance of
the hot-press resin glues would be a further help in woodworking, by permit-
ting the gluing of larger and thicker material. Such a glue may be dovelor. 3;
through research that is now in progress at industrial establishments. ?-
Laboratory's studies at present are centered on determination of maximurn
durability and strength obtainable from the resin glues and on sett.-- up
minimum performance requirements. Large-scale outdoor tests are under way
to determine the durability of the glue joints, the extent to which the face
vcnccrs resist checking, and the protective v-. lue of various surface finishes.
The-se tests- supplement thousands of small-scale accelerated laboratory tests.


xp,.ricnce in the tcstin:.- of glued veneers and plywood indicates that
products of superior quality arc the r,-cult of both good glu-i'- and. rood
cuttir,.- of the unit plies, ITo thorough,-oinj study of the veneer cuttiL..-
process in all its phases has yet been made. Research in that field contcrm-
platcd, vWith the use of equipment now available. The work in view involves
determination of methods for preparinr-- the logs, optimum conditions for vro-
ducing quality veneers from woods of different species, and methods for rL-
ducing fnstc in cutting. With all possible underlying facts developed to
guide the production of veneer, its gluing into composite form:.3, and the
testing of the products for strength and serviceability, to-ether with steady
prosecution of research in general -luing practice, paintirnw, and protective
treatments, wood will be the better prepared for effective performance in
fields of utilization both old and strictly modern.




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