Treated wood for houses


Material Information

Treated wood for houses
Physical Description:
Mixed Material
Hunt, George M ( George McMonies ), b. 1884
United States -- Dept. of Agriculture
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:

Record Information

Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 29351082
oclc - 263428608
System ID:

Full Text


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September 1935

No. I1P095

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Madison, Wisconsin
In Cooperation with the Univefaity of Wismcosi


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A wonder. buildingg properly constructed and intelligently -aintained
is in little danc-r from either decay or insect attack and will give indefi-
nitely lonj: life at lo.w annual cost. On the other hand a wooden building
constructed in defiance of the well known prirnciples of good building prac-
tice can deteriorate fairly rapidly and be a heavy expense to its owner,
The important precautions for preventing damage by decay and termites are to
keep the wood dry at all times and away from contact with the ground, and, inr.
termite infested territory, to insulate the wood completely from the ground
by the metal termite shields recommended by the U. S. Bureau of Entomologr
and others, or by any other aeans of insulation that will accomlish the same
purpose. These precautions, properly carried out, will prevent damage by
termites and decay, without the use of preservatives. In some localities it
may be necessary to take additional measures against the cr.ntrance of dry wood
termites, as recommcnded by the California committee and the Bureau of Ento-
mology, but in most parts of the couar-try tnis is not necessary. When it is
not practical to observe these precautions the use of preservatively treated
wood is important for the parts of the building in danger of attack.

Wood preservatives may be classed roughly into three general groups
having the distinguishing characteristics and general properties indicated

1. Preservative oils.--This group comprises preservative oils of the
creosote class, including coal tar creosote and its mixtures with petroleum
or tar, wood tar creosote, water gas tar creosote, and products of generally
similar character. Coal tar creosote is the most effective wood preservative
known the vorld around but, unfortunately, its color, odor, and unsatisfactory
paintin- properties limit its usefulness for treating house lumber. It is
being used successfully, however, for the sills, floor joists, first floor
subflooring and similar parts of a considerable number of houses in California
and else'-'here, with little or no objection on account of odor. Since these
parts do not require painting and are for the most part concealed the color
and unpaintabillty cause no inconvenience. Carpenters do not enjoy handling
creosoted vood, however, and do not favor its use. Carelessness in nailing
untreated finish lumber to creosoted wood may result in the staining of finish
lumber by the creosote following along the nails. In short, creosoted wood
can be used with entire success by, those who desire to take advantage of its
high effectiveness but it must be used with care.

1Published in Bulletin 4, of Pacific Coast Building Officials' Conference,
September 1935.

Report 'o. RK1095


2. Water-borne preservatives.--This group includes the various salts
that are dissolved in water and injected into the wood in this form, particu-
larly zinc chloride, zinc meta arsenite, and Wolman salts. The water must
be removed by thorough seasoning after treatment to avoid the shrinkage
troubles that result from installing unseasoned wood in buildings. The sea-
soned wood is clean, paintable, odorless, and generally suitable for use in
any part of a building. Salts that are soluble in water will gradually leach
or dissolve out of wood in contact with wet ground or frequently exposed to
water. Some salts leach less rapidly than others but no preservative salt
now in common use is immune to leaching. On the other hand, there is little
danger of leaching from lumber in buildings and no sound basis for the exag-
gerated fears that seem to be prevalent. Leaching takes place only in the
presence of liquid water. Fog and damp air do not cause leaching unless they
result in condensation and dripping of water over the treated wood.

3. Toxic chemicals in volatile, nonaqueous solvents.--This group is
of much more recent development than groups 1 and 2. It results from the
demand for a preservative that can be applied to finished wood products "in
the white," without causing swelling and distortion of the wood or inter-
fering with a subsequent finishing. Such preservatives consist essentially
of a highly toxic chemical dissolved in some cheap, volatile, organic solvent,
such as Stoddard's solvent. Other compounds may be included in the formula
for special purposes. The concentration of the toxic compound in the solution
varies according to the ideas of the manufacturer and perhaps, in accordance
with the toxicity of the individual chemicals. A commonly used concentration
is 5 percent by weight.

The convenience of these preservatives is obvious, for they are com-
monly applied by nonpressure methods and do not require kiln drying or long
air drying after treatment. The solvent is inflammable and the treating and
the subsequent evaporation of the solvent from the treated wood must be
carried out with due regard to the fire hazard involved. After the solvent
has evaporated from the treated wood, however, the fire hazard is practically
no greater than that of untreated wood.

Extravagant claims are sometimes made as to the penetrating properties
of preservatives of this type and mere surface treatments may be recommended
as sufficient. Such claims should be heavily discounted. Substantial absorp-
tion and deep penetration are required with these as with other preservatives
and they cannot be obtained by superficial methods of application.

It is a rather common belief that the effectiveness and dependability
of a preservative can be determined by a few laboratory tests. Unfortunately
this is not true. Laboratory tests can be made that give very interesting
and useful information and may show at once that a chemical proposed as a
preservative is worthless. On the other hand, if a preservative gives favor-
able results in laboratory tests it must still demonstrate what it can do in
actual use before it can be fully relied upon. There is no laboratory test
that takes the place of service tests and no standard series of laboratory
tests by which to measure a new preservative. This situation makes the
introduction of new preservatives slow and difficult and is very discouraging

Report No. R1095


to intelligent promoters who believe sincerely in the value of their pre-
servatives and are honestly promoting them.

Perhaps the first laboratory test to make on any new preservative is
to determine its toxicity to fungi. This is a purely comparative, empirical
test and the results vary according to the fungus used and the details of the
test method employed. The results cannot safely be converted into terms of
the amount of chemical required per cubic foot of wood or into years of life
expectancy. The results are useful, however, when compared with results ob-
tained in exactly the same way from preservatives whose effectiveness is
known from long experience.

Toxicity tests against termites are more difficult to make and more
uncertain in their meaning than toxicity tests against fungi. The chief
difficulty is to determine how much of the apparent effect of the chemical
on the termites results from the toxicity of the chemical and how much from
the abnormal conditions under which the imprisoned termites are made to live.
Some pioneering work was done by the California Termite Investigations Com-
mittee in devising a test and very interesting results were obtained but the
extent to which the results may be applied in practice is uncertain.

Another laboratory test of some value is resistance to leaching. This
consists in soaking small specimens of treated wood in water for long periods
of time. Analysis of the leaching water from time to time, or analysis of
the wood after leaching gives an indication of the rate at which the chemical
dissolves out of the wood. There is no standard leaching test, each investi-
gator using the conditions he considers most suitable, !ence the results ob-
tained by various investigators can seldom be compared. Furthermore, the
leaching conditions employed are usually very much more severe than the con-
ditions to which wood in a building is exposed. The results of the test do
not show how long a preservative will protect wood in actual service but
they can be 2ade to show how different preservatives compare with each other
under the conditions of the test.

Complete resistance to leaching is not necessary, even in a preserva-
tive that may be used in contact with the ground, for long experience has
shown that a preservative as leachable as zinc chloride can protect railroad
ties for many years in actual service. It is necessary for a preservative to
be soluble enough to make the vood poisonous to the attacking organisms. A
completely insoluble material would not be a preservative. Nevertheless, for
preservatives to be used in contact with the ground, resistance to leaching
is highly important and should be given considerable weight.

Other laboratory tests can be made to study the extent to which the
proposed preservative is volatile, chemically stable, corrosive to metal or
injurious to wood, safe from the standpoints of fire or health, and various
other special properties that may be required in certain fields of use. All
of these properties are important and failure to make good in some of them
may cause a proposed material to be generally rejected. Favorable results
in all of them, however, do not establish the degree of effectiveness or
reliability of any new material.

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In view of the great importance of accurate service records as a
court of final appeal in evaluating preservatives, far too little attention
is given to the subject by both producers and consumers of preservatives.
Undoubtedly this situation merely reflects the great difficulty of obtaining
adequate service records in convincing volume. Most users of preservatives
seem content with the knowledge that their wood has been treated and make no
effort to keep records on the results they obtain. Railroads and other com-
panies that use large quantities of treated wood have so much money invested
in preservatives that it pays them to watch results carefully and keep alert
for opportunities to develop improvements in cost or effectiveness. As a
result many valuable records are available on the life of railway ties,
poles, piling and similar structural material treated with the older preserv-
atives. Very few records are available, however, on wood treated with any
preservative and used in buildings. Until such records become available
preservatives for lumber for buildings must be chosen on the basis of per-
formance in other uses, laboratory tests, and/or faith in the integrity and
scientific knowledge of the promoters.

The treating problem does not end with the choice of the preservative.
For a preservative to provide satisfactory protection it must not only be of
suitable quality but it must be thoroughly impregnated into the wood in ade-
quate quantity. Claims to the contrary notwithstanding, it is too much to
expect brush, spray, or dip applications of even the best preservatives to
give long life to wood exposed to conditions that favor rapid decay or heavy
termite attack. Such superficial treatments do not penetrate deeply. They
provide an outer envelope of treated wood so thin that it is easily abraded
or checked through and both termites and decay can readily find and penetrate
the weak spots. Surface treatments may sometimes be used to advantage but
they are not to be relied upon for the protection of valuable buildings ex-
posed to serious attack by decay and termites. Pressure treatment, skill-
fully applied, or at least a substantial absorption and distribution of pre-
servative are required for best results. Hot and cold bath treatment may
sometimes be used as a substitute for pressure treatment but is likely to be
less effective.

The lumber should not be cut into after treatment if that can possibly
be avoided. Cutting after treatment may expose untreated wood to attack and
thus defeat the purpose of the treatment. The simple method, but not the
best, is to purchase the treated lumber in the usual commercial lengths and
have it cut to size on the job. A little planning by the architect and a
little cooperation on the part of the lumber dealer or treating plant oper-
ator, however, can provide treated material that does not need to be cut into
on the job. When cutting into untreated wood cannot be avoided the cut faces
should be protected by brush application of a suitable preservative but the
penetration obtainable in this way is too slight to repair the damage

A major difficulty in the way of house builders desiring to use treated
lumber is the inaccessibility of the treated material to most prospective
users. In a few localities, due to the proximity of treating plants or of
lumber yards that carry stocks of treated material, it can be obtained as

Report NIo. R1095



required. In other localities it is necessary to make a special order of i
the treated material and have it shipped in by a treating plant or jobber.
This may be both inconvenient and expensive and is likely to discourage the .
builder from using treated wood. Everything possible should be done by i7
lumber treaters and lumber dealers to make treated lumber economically ac-
cessible wherever lumber is sold. This is not easy to accomplish and proW
ress is likely to be slow. In the meantime the prospective builder who
cannot conveniently obtain treated lumber may still erect a durable building
if he will but obey the rules of good building practice. Moat decay and
termite damage in buildings can be traced directly to disobedience of these

3 1262 08928 0365

Report No. R1095