Preservative treatment of window sash and other millwork


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Preservative treatment of window sash and other millwork
Physical Description:
Mixed Material
Hunt, George M ( George McMonies ), b. 1884
Forest Products Laboratory (U.S.)
University of Wisconsin
U. S. Department of Agriculture, Forest Service, Forest Products Laboratory ( Madison, Wis )
Publication Date:

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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 29347065
oclc - 499883575
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Madison, Wisconsin
In Cooperation with the University of Wisconsin
Revised, April 1938

/ /

Digitized by the Internet Archive
in 2013




George M. Hunt, In Charge,
Section of Wood Preservation.

How important is decay resistance in woods used for window
sash? How important is it in frames, shutters, floors, and millwork in
general? These items are not commonly destroyed by decay because the
conditions under which they are placed are not favorable to deterioration.
The average owner or occupant of a dwelling, store, or office building
seldom encounters an instance of decay in the sash or interior woodwork
of the building. On the other hand, every manufacturer of wooden window
sash or frames and every carpenter who does repairing can point to
numerous instances of replacement made necessary by decay.

The total number of wooden frames, sash) and shutters manu-
factured in a year is in the millions. :Io statistics on the number that
show decay under ordinary use conditions are available; an expensive
and time-consuming survey would be required to furnish a satisfactory
basis for merely an apprQxinate estimate. Probably, however, the per-
centage is small. Yet, although the number of instances of decay may be
low, the matter cannot be ignored. It is far from immaterial to those
who have to pay for expensive repairs caused by premature decay, and the
manufacturer who loses the business or the good will of these displeased
customers can hardly afford to consider it trivial. On the other hand,
it is hard, without definite information as to the extent of the need)
to justify any marked increase in cost of all sash and frames to protect
the small percentage that may need it.

A factor of some importance is the modern trend towards air
humidification and tighter window construction, especially in the colder
parts of the country. Both favor the maintenance of higher humidities
in buildings in the winter than have been customary in the past, which
encourages the condensation of moisture on windows in cold weatherr and
tho collection of moisture in walls. It is reasonable, therefore; to


expect an increase in the amount of trouble from decay as well as from sap
stain in windows, beyond what has taken place in the past-1

In industrial buildings of certain types, w''::re it is known from
experience that sash and other woodwork will be sub,.k to decay on account
of the service conditions, there is no question that decay resistance
should be provided. Experience has shown that the use of metal sash is not
a satisfactory solution of this problem in industrial buildings where high
humidities prevail, especially if there is any acid in the air, but veood
sash thoroughly impregnated with a good preservative have been shown to
be very durable in such places. All-heart sash of highly decay-resistant
woods that are suitable in other respects may also be used successfully.

In the competition between wood and metal sash for dwellings and
office buildings, lack of decay resistance in untreated wood sash is a
sales disadvantage for wood that itd competitors have not neglected, and
the wood sash manufacturers can afford to make some attempt to overcome
this obstacle. For this reason, as well as to reduce the number of cases
in which decay or staining takes place, the treatment of all sash made
from wood of low decay resistance has much to recommend it, providing it
can be done effectively at moderate cost.

The Relative Decay Resistance of the Soft Pines

A question frequently asked is how the various pines now used
for sash compare with one another in decay resistance. The question arises
in part from the desire of the manufacturer and the user to know more about
the subject, and in part, no doubt, from the conflicting claims made by
the promoters of competing species. As a matter of general knowledge it
would indeed be interesting to know just how northern white pine (Pinus
strobus), western white pine ("Idaho white pine," Pinus monticola), sugar
pine (Pinus lambertiana), and ponderosa pine (Pinus ponderosa) compare
with one another in average decay resistance. Since these woods, when un-
treated, are not ordinarily used in contact with the ground or in other
places where conditions are known to favor decay, there are no adequate
service records on which to judge them. Furthermore, they have not built
up a body of experience and general knowledge of their decay resistance

-In the northern part of the country the use of storm windows will often do
much to reduce condensation on windows and the consequent danger of stain
and decay. Weatherstripping is useful for reducing infiltration of air
around windows but it does not keep the glass from becoming cold enough
for condensation to gather. Storm windows, on the other hand, kuep the
Inside panes of glass much warmer and cut down loss of heat through the
windows. House owners should take care to see that they do not havo
excessive condensation on their windows. When cooking, bathing, or
laundry work loads to condensation during cold weather, windows or doors
should be opened -sufficiently to ventilate the house or the room and
carry out the cxcoss moisture, even though a little more fuel may be
reqo1tr3d. to kfoep thbi hoiso warm.

such as that available on the woods more commonly used outdoors in
fences) pole lines, and railroad ;ird other engineering structures. At-
tempts have been made to work out laboratory methods for accurately cor-
paring the decay resistance of different species but thus far none of the
suggested methods has been found acceptable. It is impracticable, there-
fore, to set up a table of relative decay resistance for these species
and defend it successfully, whatever one s personal opinion may be.

Heartwood and Sapwood

A well-known fact about all the commercial woods of the United
States is that) under dry conditions, both the sapwood and heartwood
remain free from decay but; under damp conditions, the sapwood is not
resistant to decay, regardless of the durability of the heartwvood. The
sapwood of such natlr.-lly durable species as redwood, cedar, and cypress
rots quickly under conditions that favor decay and so does that of the
pines and other species. Whether there is a measurable difference between
the decay resistance of the sapwood of a species having highly durable
heartwood, and the sapwood of one having less durable heartw'ood, has not
been established but, even if a slight difference does exist, it is not
enough to be significant. The outstanding fact is that, where decay re-
sistance is required, no sapwood should be permitted unless it has been
adequately treated with a toxic preservative.

There are no restrictions on sapwood in lumber used for
ordinary sash and frames. If used under conditions that are not con-
ducive to decay, their life is not affected by the presence of the sap-
wood, Under conditions favorable to fungus growth, however, the sapwood
invites early stain or decay, whether the heartwood is durable or not.
So long as the practice continues of allowing unlimited amounts of sap-
wood in window sash and frames, there is little point to the debate
over the relative decay resistance of the various pines that are now being
used for those purposes. If a sapwood corner rots in a window sash or
if the sash lift pulls out because of decay it is small comfort to the
man who has to buy a new sash to know that the heartwood parts of the
discarded sash are still sound*

A defect often encountered in sash and frames and chargeable
to sapwood is the black or blue stain that develops when the wood takes
up moisture and remains damp for considerable periods of time. It is
merely a sap stain fungus growing after the installation of the finished
article in the house instead of growing while the lumber was in a yard.
The stain, when it occurs, is readily visible through varnish and fre-
quently breaks through varnish or paint, to the discorfiture of the
painter, who usually gets the blame. Since sap stains do not grow in
heartwood, this defect is found only when sapwood is present and then
'nly under damp conditions. While these stains do not destroy the wood



they may necessitate its removal on account of its appearance. The:r also
indicate that conditions are favorable to decay and should be corrected.-

In addition to the staining caused by fungi that grow in the
wood, molding or staining of the paint may occur that does not extend into
the wood. kuch staining cannot be attributed to the wood, but it is an
indication that conditions are favorable for wood staining and decay and
that they should be corrected.

Improvement Through Selection of Wood

A simple way to provide high decay resistance (although not
necessarily the most practical or the most economical) is to make the
sash) frau:.r.s, or shutters nut of naturally durable wood. The heartwood
of certain species high in decay resistance can usually be counted on for
long service even under conditions that favor decay. Then questions of
available supply, cost, appearance, working properties, and mechanical
properties are taken into account, however, these species do not have un-
disputed superiority over the woods now commonly used for sash and frames.

Protection Through Painting

Contrary to popular belief, paints and varnishes are not ef-
fective in preventing decay. Wood used under conditions that favor decay
can rot readily, whether it is painted or not. If paint could be relied
upon to prevent the absorption of moisture and thus keep the wood always
dry, decay would of course be prevented, for it is the presence of
moisture in considerable quantity that permits decay. Wood that is well
painted on all surfaces does absorb moisture more slowly than unpainted
wCood but the absorption is not prevented entirely. It is seldom, however,
that wood is painted on all surfaces and moisture absorption is not re-
tarded in the least through the unpainted surfaces. Moisture can usually
find access also at joints, where the paint cracks because of repeated
dimension changes in the wood or the working of the joints. Moisture th-it
has found access to the interior of painted wood will evaporate more
slowly than from unpainted wood. When this happens the paint may favor
rather than retard decay.

Paints and other finishes do not prevent the development of
blue stain, If conditions are favorable to the development of the blue
staining fungi they grow, regardless of the paint that may be over them.
If conditions are sufficiently favorable the staining funcgi grow right
through p-int or varnish and repaintin, does not prevent their reappear-
.nce if the damp conditions are allowed to continue. Furthermore, as
previously stated, fungi may grow in the paint itself and cause discolor-
A tion wJitho it rf.ic-_r th_wood. ______________________
Once the faulty condition has been corrected blue-stained sash may be
safely repainted provided they are first given time to dry out thor-
4y1.hJ It may be desirable to r-move the old paint before repaintin>



Preservative Treatment

Preventing decay in wood by injecting toxic chemicals is easy,
Preservatives and methods of treatment have long been available that car.
be relied upon to give to wood, even sapwood of low natural decay re-
sistance, very long life under the most severe decay Pxpesure. rh y
will also prevent sap stain development. The problem of treating to
meet the special requirements of wood for use in window sash, frames,
and other millwork, however, is not easy of solution. For example, no
more effective preservative than coal tar creosote is known, but it is
obviously unsuitable for use in the windows or millwork of a house be-
cause both the color and odor of the creosote are objectionable, and
creosoted wood cannot be satisfactorily painted or varnished.

Water Borne Preservatives

There are several good preservatives that can be injected in
water solutions by pressure methods. Drying out the water after treat-
ment leaves the wood clean, odorless, and paintable, although often
changed in color to some extent. If the work is properly done and if
the pieces in any way degraded by the treatment and subsequent drying
are eliminated, the purchaser will receive a good product that is highly
resistant to decay. It is quite possible to produce well-treated frames
and sash in this way. The treatment is far from being as si-ple as it
sounds, however, and the inconvenience and expense involved have pre-
vented most sash and frame manufacturers from attempting to use water
borne preservatives.

Treatment of Lumber Before Milling

One procedure that may be followed in using water solutions is
to treat the lumber by a pressure method before cutting it up and mill-
ing it. When this is done the lumber must obviously be completely pene-
trated and the preservative should be distributed through it uniformly.
Spots of untreated or poorly treated wood in the interior of a board
will almost exposed when the board is milled to finished
size and shape, and under conditions favorable to fungus growth these
vulnerable spots will be "welcome" signs to fungi. Complete penetration
in sapwood pieces of most species up to 4 inches in thickness should
offer little difficulty if pressure-treating equipment is available and
proper treating conditions are used. Excellent treatment can readily
be obtained, therefore, wherever it is possible to select for treatment
lumber that contains no heartwood., It is more difficult to obtain

AThe superiority of heartwood over sapwood in decay resistance when un-
treated is of no significance in wood that is properly treated, for
good preservatives properly injected prevent decay in both heartwood
and sapwood.



complete penetration in heartwood, but it is not impossible if the boards
are not too thick. Considerable difficulty is likely to be encountered
in completely penetrating heartwood pieces 2 inches thick or over. Dif-
ferent species of wood vary somewhat in the resistance of their heartvwood
to treatment but in practically none of them can the heartwood be con-
sidered easy to treat.

Treatment After Milling

Preservative treatment may be applied to the finished frames
or sash after assembly, or to the individual finished pieces just before
assembly. Both periods of application have the advantage that complete
penetration is not necessary, for there will be little or no cutting
after treatment. When using water solutions, however, treatment after
assembly involves a number of difficulties. Injecting water into the
wood will m-ke it swell, probably causing, in consequence, either actual
rupture of joints or at least compression severe enough to result in
open or loose joints on subsequent drying. The checking and distortion
that may develop in some of the assembled parts upon Ilrying will cost
more than a similar amount of warping or checkiniL in the rough lumber
would cost. Any joints containing glue may be seriously affected by the
water and, furthermore, the surface of the wood may be so roughened that
resurfacing will be required. Altogether, the outlook for the treatment
of assembled sash with preservatives in water solution does not seem
bright but, in some cases, it may be found practical. Treatment of the
finished parts before assembly would not cause loose or open joints but
grain raising) warping, checking, and drying problems would still be
encountered. Undoubtedly; however, water borne preservatives can be
used to advantage under some conditions.

Special "Sash" Preservatives

During the past few years a number of proprietary preservatives
have been developed especially for the treatment of sash and similar pro-
ducts. Generally they consist of an organic toxic chemical carried in
a nonaquleous volatile solvent. They are practically colorless and dry
quickly by evaporation of the solvent. If of suitable cinracter they
leave the wood clean, paintable, and practically odorless.

Various toxic chemicals have been used in these formulas, in-
cluding alphanitronaphthaline, betanaphlithol, chlorbetanaphthol, chlor-
orthophenylphenol, metallic naphthenates, pentachlorphenol, and tetra-
chlorphenol. This list by no means exhausts the possibilities and it
is very probable that other toxicants will be found that are as good or
better. The relative merits of the toxicants named have not yet been
worked out satisfactorily, but all osen to bi suffdicontly toxic to be
effective, provided th. y constitute not less than 5 iporcent of the treat-
ing solution (by weightt. Since these toxicants differ in cost, odor,
solibility, and other properties it is to be expected that, as the
nLwr.-jI;.-' aboht them iizr~ w. throi4h research and *:xpoirience, some



will be found more desirable than others. Considerable work in this field
is being done by the Western Pine Association, as well as by some sash
manufacturers and manufacturers of toxic chemicals, and a grad.-al change
and improvement in formulas is to be anticipated for some years to come.

In some formulas drying oils, such as linseed oil, have been
used for the purpose of "priming" the sash and =r-ing it water resistant.
This practice is not to be recommended, for it fails to give the sash
any material resistance to moisture or to provide an adequately primed
surface, but it may reduce the effectiveness of the toxic chemical.
Even dipping in pure linseed oil is not effective in priming or water-
proofing wood, and dipping in diluted solutions is less so.

Nondrying petroleum oils are sometimes advocated as an ingredient
of sash treating preservatives. It is possible that the addition of a
substantial amount of such oil may have an undesirable effect on paint or
putty subsequently applied to the treated sash. Considerable time and
experimenting will be required to deter:nini' the extent to which this
possible disadvantage actually exists. In the meantime) it is not en-
tirely safe to ignore it.

The degree of effectiveness of the s 'cial sash preservatives
in preventing decay, blue stain and insect attack has not been definitely
established. Laboratory experiments have indicated that they should
give good protection if the wood is properly impregnated with a substan-
tial quantity. It is believed, therefore, that the use of sash preserv-
atives is desirable. Long continued observation and experience with
treated sash under actual use conditions will be required, however, to
determine the extent to which the promise of the laboratory experiments
is borne out in actual service.

In order to choose intelligently among the various sash pre-
servatives it is important to know their composition. The term "wood
preservative" ie used very loosely by some makers of paint and varnish
materials and there are products on the market which have been recom-
mended for sash treatment that contain no toxic ingredients. Others
may contain ingredients that are not sufficiently effective or that are
present in insufficient quantity. Such materials cannot reasonably be
expected to afford satisfactory protection against decay or stain. A
secret formula leaves the purchaser without information as to the
presence of a toxic ingredient, its nature, or the amount present in the
solution, all of which are very important in considering the probable
effectiveness of the material. Furthermore, the composition of a secret
preservative may be changed at will by the manufacturer or seller, with-
out the knowledge of the consumer. When the composition is disclosed
the purchaser has something definite for consideration, both as to cost
and, probable effectiveness, and he may also make occasional analyses or
tests to determine whether the quality remains the same. Enough pre-
servatives of known composition are available to make it unnecessary for
anyone to purchase secret preservatives.


7ith a good preservative of this character, treatment can be
made after firishiig the parts, either before or after assembly. There
is no swelling of the wood and no drying out of moisture after treatmentJ
with its accompanying troubles. Penetration need not be complete but
it must be deep enough to ir.s-re against exposure of untreated wood when
the carpenter trims the frame or sash on installing it. -,uch exp;.'e
can be avoided by fitting the sash to the frame in the factory and
treatil.!: after fitting. If the wood is sound to begin with, maintaining,
a substantial depth cf treatment at all surfaces and in all joints will
prevent decay or untreated wood that may be beneath* It is when the
treated area is broken through by cutting or checiL'.,- or by the opening
of poorly treated joints that the untreated wood beneath can be rea."-,
by the fungus.

Importance of Good Treatment

Obviously, good treatment is needed) in addition to a good pre-
servative, for even the best preservatives cannot give much protection
if not properly applied. Although complete penetration is not required
in treating finished ports, substantial penetration is necessary. re-
markable penetrating pc'.'rs are not infrequently claimed for proprietary
treating oils so that a brief dipping treatment is often said to be
all that is required to give deep penetration with them. "7ith a suit-
able preservative -n appreciable amount of protection can no doubt be
obtained by a few minutes submersion but better penetration and con-
se7uently better protection will be obtained by .-ir.g longer soaking
period.; or more thorough treating methods. :he 71estern Pine Association
reccrrmends an immersion period of not less than 5 minutes. This is long
enough to give a -ubstantial degree of protection. ..'rter periods are
nde....irble and longer one s are to be preferred.

On account of the high volatility of most of the solvents
employed in special sash preservatives, it is usually impractical to
heat "1. ;. ]. effect of a hot-and-cold bath treatment can be accom-
plished by heating the wood in a properly controlled kiln and then
submerging it and allowing it to cool in a tank of cold preservative.
This heai.od has been patented. A similar effect can be obtained by
placing the sash ir. a closed container; drawing a vacuum, and admitting

'_ I.'. - i* h__" _

Jinc, the special sash preservatives are pr--'tically colorless
it i.; vw,,,, difficult and usually impractical to detect their presence
in tnhe vocd aftUr the sash have been. in service some time. It is very
deirabe, therefore, that sash manufacturrers place a permanent brand
cr identification mrare on their products, givir., the date and some mark
to ide-nti -, the presoe.rvative and method of treatment. This will permit
fi]i ura s to be traced to their sources and aid in pointirng the way to
impro'-n It will aiso be of value in identifying products that
iv lor.t "i.d statis factory service.


Treatment for Industrial Buildings

In certain types of industrial buildings, where the require-
ments for appearance are not too strict and where it is certain that high
decay resistance is required, the problem of protecting sash and frames
is not so difficult as for dwellings. The purchaser, knowing the need
for high decay resistance, is prepared to pay the cost of getting it.
Appreciable quantities of sash treated with water borne preservatives
have been installed in dye houses, textile mills, paper mills, and the
like. In at least one case the sash and frames in a locomotive round
house were creosoted and left unpainted. The result was considered
much more satisfactory than that obtained with untreated wood or metal

Specifications for Sash Treatment

Standard specifications covering acceptable preservatives and
methods of treatment for sash and similar products arc highly desirable
in order to avoid the confusion and doubt that are certain to arise in
the minds of architects and consumers because of co flicting statements
made by promoters and users of various sash treatments. Attempts are
now being made by organized sash manufacturers to bring this about. The
early adoption of good specifications that can be used by both producers
and consumers will be very helpful.

Clean Treatment of Other Products

Although the foregoing discussion has been limited mainly to
sash and frames it has general application to other products, including
shutters, flooring, finish lumber, garage and other outside doors, auto-
mobile body parts, refrigerator parts, partitions, office equipment, and
furniture, when they are to be used under conditions that require re-
sistance to decay or insects. Under the conditions that ordinarily pre-
vail in buildings throughout most of the United States no preservative
treatment is r-quired for floors, partitions, interior finish, lumber,
or furniture, but it may be required in special cases or for use in warm
humid climates, when it is known in advance that service conditions will
be severe.

Moderate resistance to termites, as well as decay resistance,
can be obtained by the use of heart redwood or heart cypress in products
for which these woods are suitable. For other products or for other
Arerican woods, or where maximum termite and decay resistance is required
preservatives should be used.

With wooden refrigerator parts, and with any other wood that
is to be used in close proximity to food, especial consideration must be
given to avoiding odor and contamination. Toxic chemicals that endanger
health must be avoided in treating wood that is handled frequently, or
that will be used in interiors of buildings.



Results to be Expected

It is not possible to predict with certainty the number of years
cf additional service that can reasonably be expected from treatment of
sash and similar products. The conditions of service have much to do with
the result. Thorough impregnation with coal tar creosote under pressure,
resulting in absorptions of 12 pounds of creosote or more per cubic foot
of wood should give complete decay protection to sash, doors, and similar
products throughout their mechanical life or the useful life of the
building in which they are installed. Creosote treatment, however, is
seldom acceptable for such products.

Thorough pressure treatment with reputable water borne pre-
servatives should give about the same results as creosoting in situations
where the wood may be damp but will not be exposed to the lcachirn effect
of constant or frequent contact with free water. Where service conditions
favor leaching water borne preservatives will be less effective than

The special sash preservatives containing not less than 5 per-
cent of a stable and suitable toxicant have not been in use long enough
to have shown by their perfor,,r nce in actual service just how they corm-
pare in effectiveness with creosote and water borne preservatives. Labo-
ratory tests and such limited service tests as are available, however)
indicate that they should give satisfactory results. It is reasonable,
on the basis of the information thus far available, to expect these pre-
servatives to give satisfactory protection when they are thoroughly im-
pregnated into wood in substantial quantities.

Most sash and similar products are not used under the most
severe servicee conditions, and consequently they do not require the neavy
treatment necessary for outdoor structural timbers. simple imm.ersion
for 3 minutes or longer in special sash preservatives of high quality
is probably sufficient to prevent decay in sash in ordinary homes and
office buildings, if the treated wood is not trimmed off in subsequent
fitting operations. Where conditions are very favorable to rapid decay
or stvin, more thorough impregnation is considered necessary for ad' _.ate

Dipping for a few seconds in any preservative E ives only a
slight degree of protection. and is not considered adequate for general



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