Preservative treatment of window sash and other millwork


Material Information

Preservative treatment of window sash and other millwork
Series Title:
Report ;
Physical Description:
12 p. : ; 26 cm.
Browne, F. L ( Frederick Lincoln ), 1895-
Forest Products Laboratory (U.S.)
University of Wisconsin
USDA, Forest Service, Forest Products Laboratory
Place of Publication:
Madison, Wis
Publication Date:
Rev. 1945


Subjects / Keywords:
Millwork (Woodwork)   ( lcsh )
federal government publication   ( marcgt )
non-fiction   ( marcgt )


General Note:
Caption title.
General Note:
"In cooperation with the University of Wisconsin"--Cover.
General Note:
"Revised March 1945"--Cover.
Statement of Responsibility:
by F.L. Browne.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 029318526
oclc - 228444359
System ID:

Full Text


Ievised March 11945

/TO--F N.

No. IP919

Madison, Wisconsin
In Cooperation with the University of Wisconsin



S. L. BO0I-LE, Chemist

How important is decay resistance in woods used for window sash? How
important is it in frames, shutters, floors, and millwork in general? .'hese
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 in-
stance of decay in. the sash or interior woodwork of the buil.ii. 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 manufactured in
a year is in the millions, -o statistics on the number that show decay under
ordinary use conditions are available; an expensive and time-coni.rumin- s'.irvey
would be required to furnish a satisfactory basis for merely an approxi-mate
estimate. Probably, however, the percentage 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 humidifi-
cation and tighter window construction, especially in the colder parts of
the country. Both favor the maintenance of higher humidities in buildin;-'s
in the winter than have been customary in the past, which encourages the
condensation of moisture on windows in cold weather and the 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, be-
yond what has taken place in the past.1

-In the northern part of the country the use of storm windows will often do
much to reduce condensation on windows and the consequent dar.--er of stain
and decay. 'featherstripping is useful for reducing infiltration of air
around wi!.dows but it does not keep the glass from becoming cold enough
for condensation to gather. Storm windows, on the other hand, keep 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 have ex-
cessive condensation on their windows. When coo'rinr-, bathing, or laundry
work leads to condensation during cold weather, windows or doors should
be opened sufficiently to ventilate the house or the room and carry out
the excess moisture, even t..r.o.-!. a little more fuel may be required to
keep the house war::.

Report 17o. R919 (Revised)

In industrial buildings of certain types, where it is known from ex-
perience that sash and other woodwork will be subject 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 satis-
factory solution of this problem in industrial buildings where high humidi-
ties prevail, especially if there is any acid in the air, but wood 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 its 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 iiade 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 pro-
moters of competing species. As a matter of general knowledge it would
indeed be interesting to know just how Eastern 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 untreated, are not
ordinarily used in contact with the ground or in other places where condi-
tions are known to favor decay, there are no adequate service records on
which to judge them. Furthermore, there exists no fund of experience and
general knowledge of their decay resistance such as that available on the
woods more commonly used outdoors in fences, pole lines, and railroad and
other engineering structures. Attempts have been made to work out labora-
tory methods for accurately comparing the decay resistance of different spe-
cies but thus far none of the suggested methods has been found acceptable.
It is impracticable, therefore, to set up a table of relative decay resist-
ance 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 re;;.ai. free
from decay but, under damp conditions, the sapwood is not resistant to de-
cay, regardless of the durability of the heartwood. The sapwood of such

Report :To. R919


naturally durable species as redwood, cedar, and baldcypress 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 resist-
ance of the sapwood of a species having highly durable heartwood, and the
sapwood of one having less durable heartwood, 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 resistance is required, no sapwood
should be permitted unless it has been adequately treated with a preserva-

There are no restrictions on sapwood in lumber used for ordinary sash
and frames. If used under conditions that are not conducive to decay, their
life is not affected by the presence of the sapwood. Under conditions fa-
vorable 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 sapwood 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 sap':ood 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 sap-
wood is the black or blue stain that develops when the wood takes up mois-
ture 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 frequently breaks through
varnish or paint, to the discomfiture of the painter, who usually gets the
blame. Since sap stains do not grow in heartwood, this defect is found orl'r
when sapwood is present and then only under damp conditions. Althoue:. these
stains do not destroy the wood they may necessitate its removal on account
of its appearance. They also indicate that conditions are favorable to de-
nay 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. Such strtinin; cannot be attributed to the wood, but it is an indica-
tion that conditions are favorable for wood staining and decay and that the:-
should be corrected.

Improvement Through Selection of -'rod

A simple way to provide high decay resistance (although not neces-
sarily the most practi,-cl or the most economical) is to m: the sash,

-Once the faulty condition has been corrected blue-stained sash ':a be
safely repainted provided they are first given time to dry out thoroug,-hl-.
It nmav be desirable to remove the old paint before repaintii.:.


'., ort To. Y)19

frames, or shutters out 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. When questions of available supply,
cost, appearance, working properties, and mechanical properties are taken
into account, however, these species do not have undisputed superiority over
the woods now commonly used for sash and frames.

Protection Through Painting

Contrary to popular belief, paints and varnishes are not effective 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, de?'y
would of course be prevented, for it is the presence of moisture in consid-
erable quantity that permits decay. Wood that is well painted on all sur-
faces does absorb moisture more slowly than unpainted wood but the absorp-
tion is not prevented entirely and, if the exposure to dampness lasts lonu
enough, the wood will become saturated and will swell as much as unpainted
wood does. It is seldom, however, that wood is painted on all surfaces and
moisture absorption is not retarded in the least throiih the unpainted sur-
faces. Moisture can usually find access also at joints, where the paint
cracks because of repeated dimension changes in the wood or the uor1'.1: of
the joints. Moisture that has found access to the interior of painted wood
will evaporate more slowly than from un-oainted 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 condi-
tions are sufficiently favorable the staining fungi grow right through paint
or varnish and repainting does not prevent their reappearance if the damp
conditions are allowed to continue. Furthermore, as previously stated,
fungi may grow in the paint itself and cause discoloration without reaching
the wood.

Preservative Treatment

Preventing decay in wood by injecting toxic chemicals is easy. Pre-
servatives and methods of treatment have long been available that can be
relied upon to give to wood, even sapwood of low natural decay resistance,
very long life under the most severe decay exposure. They will also prevent
sap stain development. The problem of treatin.- to meet the special requ-ire-
ments of wood for use in window sash, frames, and other millwork, however,
is not so 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 because both the color and odor of the
creosote are objectionable, and creosoted wood cannot be satisfactorily
painted or varnished.

Report To. R919

-Za- Tam: 7=- 1
:- -- .-e - - ----' -i -.- --. .h-. "-e --- --e -- -1
.::u'..'n-" ----.:_r = h: -- ..- -u :h w a: .. "-=-=mn lae

--- ex-. n:. : e .... ---... i-er -. .. h : s i :' -' =

:-= --= --: -- --.---'- "- u -- --?'-,- -,- ---- ini- --- -<' ... _---. =

F--- -

.. . . .. .- .. .. ; _- e _.-:_ :-

-: -' '- "-': -- = -_ :: '=_-_ --- -- i - -----. A _- 4 .-- - - - .. .. =' = n

-.- =- n um:_r b 7-e- '--- : .- ---~r ---.i n -- -- -- ---- .. ---:! -

.. .. ... ..: :i .n in.e-i= -- Z -i -l l_ =-i- h

"-- -- -- -'----- Fe i [ = ... : - .. .. --- - --m -- "' -- [ i-

r i r i c < : : e ---- -

-_- _- f }i l -_-_- *-
7e z
7:rv~~ 7 '-=:-e":-' t r l e : h i-in f e r =-

:<-~~~~~~~~~~~~~ ~~~~~~~ z- :r f- hr ~ -; i-l =--- : f -- .. ."

--------._-he--------:--.-.:--and ----o---"--.
td .z oe ,o' se _> h : .... ... :ha e:,:a-iv~- L sn f:. ze
--.l~ ze r.a- uo: :. :-.e:~a~ --~r a:e _c
s btll er:. will waste _cre er eaa- a -:ilara: .... -
wa_ .- s.-_ orC-eckrnz int. :ie ru:h: e. ."--* c nn lent :
_: e a e -7he wee- ner.e, :hn= eof h

Z- a- ree So~ n;4 _
-"h er a to- a --- a e" ,7i

:0 woaw' a'zne :-:fse ur-c a : e::

7- 7- e S 7' : Z
arS s c: :c-, a- I a e- --
a_ e=a _o er.:L :.. a: : -.zx : a l: e iC e '-

- -e r7 la,4 'e s ..ere.. .. 4 e
-se :em-e r: :n s: z-ee7e aarts 7: e z-a

.e..c i .... .... a .... =i i ane r -"
ise e. en e e.e... i "'_--en -a,; .- a-i:: ---= -'= ^i

e:'er4-e a-:'E:.v
w"v(.~.... _i a !a-re ervatiesi --a- :-5: se----2- ....
's i o : ". 'a' 2se-- 'dcc to --s ell 1 ;iX : rea_ zer. : &_.__: e -,.. ......~ 7
i _-~ ... e i fu ortheer- ...~ e. Thes =I--l i ?_reie: -hCe :re-

D r:_ atesi re : pra~e v^e :4ie z h:ar e a
d-e- e"l O 1,:s c- cW ] n e ....
w--', ch ha ......' -,-- aI I C "- S--q'i -E :*f -: -e na-
the. +-^'me sash, z{=.;.fa--e---, -ea---.-:. c-,-
wihu ::ree.e a,:-- a- ;e:/p_ 7eL~s Zr 7 t:Zi:i
^a-.s _oc,; P- se 1a:!ie ~ c z r e----;

_e h a~:a :.:-r hat "=erer."se! ::ia rres zvc:i:e : :_ -.

e74: a-: . f-o _i-_ .h .e... .
-he reiat '-'v e r of -a noanv l a e . .-- e s w r e: --

nare o "'7--- e e T:e . 7a ... s.. = m f i ; n ; o = :=- 3 _. -i 'l :. 2
-m er ert ":e -non'-- --we -e z-
ta, RC .. .. Sa : e = = --. .

are also active in this work. Wartime problems have stimulated, use of the
1ISP preservatives for wood prod.,,ts other than sash and millwork. Gradual
change and improvement in the preservnf lives and extension of their use to
other fields are to be expected for some years to come.

!:.e ',SP preservatives in.y well be divided into two types according to
the presence or of vate-'-2repeilent in;rc-t.,ents. Those without water
repellent consist yin call cf a so .in:t o"-ic In vya4:,o petroleum
solvent such as miier--l spirits cr Stcdo.t'v ( i. i-et ant, in a3iAition, may
contain a proportion of l3s volatile su,' ent. sch a;. fp.el c:l, to facili-
tate spreadinr< of Che preservrative tr "bloo,.-n" (c Ilectionr of scrys -cs of s1tL o.i r,' - the solvent eotnor, es)r. Other special ,oiens- :-i iu:_ to- improve the
solubility of the toxic and to prevent "'sluoj, s. j' cca on of ingredients
from solutiion) 1Ahile in dip- tal,-s or in stora. e. Freae:-vatives containing
water repellents are discussed further on in this paper under the heading;
-..TP "'Iter-repellent Preservatives. "

The degree of effectiveness of the i'S' preservatives in preventing
decay, blue stain, and insect attack has not been sufficiently established.
Laboratory experiments have inc-i',ated that they should ,,.ive good protection
if the wood is properly imreg'ated with a substantial qiiuantity. Even the
3-minute immersion treatment. ., -Lch is now cotL.only used with sash and simi-
lar items, appears to be giving good re -ults in ractiJce. It is believed,
therefore, that the use of -"..' --rsse:v- is deFi-able for millwork that
contains sapwood. Long continued obser'-:tion and experience with treated
sash under actual use conditions will be :"eq,ired, however, to determine the
extent to which the promise of the laboratory experiments and limited ex-
perience is borne out in general service over long periods of time.

In order to choose intelligently among the various l;p preservatives
it is important to know their composition. The term "wood preservative" is
used very loosely by some makers of paint and varnish materials and there
are products on the maarket which have been recommended for sash treatment
that contain no toxic ingredients. Others may contain ingredients that are
not sufficiently effective or that are present in insfficient quantity.
Such materials cannot reasonably be expected to afford satisfactory protec-
tion 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 consider-
i..; the probable effectiveness of the material. Furthermore, the covnposi-
tion of a secret preservative may be chanied at will b' the manufacturer or
seller, without the knowled c of the consumer. When the composition is dis-
closed, the purchaser has something definite for consideration, both as to
cost and probable effectiveness, and he m.ay also make occasional analyses or
tests to determine whether the quality remains the same. Enough preserva-
tives of known co,,.position are available to make it unnecessary' for anyone
to purchase secret preservatives.

Report ITO, R919

Importance of Good Treatment

Obviously good treatment is needed, in addition to a good preserva-
tive, for even the best preservatives cannot give much protection if not
properly applied. Although complete penetration is not required in treating
finished parts, substantial penetration is necessary. Remarkable penetrat-
ing powers 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. With a suitable preservative an apprecia-
ble amount of protection can no doubt be obtained by a few minutes submer-
sion but better penetration and consequently better protection will be ob-
tained by using longer soaking periods or more thorough treating methods.
The National Door Manufacturers' Association recommends an immersion period
of not less than 3 minutes. This is long enough to give a substantial de-
gree of protection. Shorter periods are undesirable and longer ones are to
be preferred.

Penetration of preservative must be deep enough to insure against
exposure of untreated wood when the carpenter trims the frame or sash on
installing it. Such exposure can be avoided by fitting th h-ah to the
frame in the facoCy and treating after fitting. If the &'1O is sound to
begin with, mali ining a substantial depth of treatment at all surfaces and
in all joints ;i.l prevent decay of untreated wood that be beneath. It
is when the treated area is broken through by cutting or checking or by the
opening of poorly treated joints that the untreated wood beneath can be
reached by the fungus.

On account of the high volatility of most of the solvents enmroloyed
in 1TSP preservat-ives, it is usually impractical to heat them. The effect of
a hot-and-co-LC' -bath treatment can be accomplished byr heating the wood in a
properly controlled kiln and then,'ing it and allowing it to cool in a
tank of cold preservative. This method has been patented. A similar effect
can be obtained by placing the sash in a closed container, drawing a vacuum,
and admitting preservative without admitting air or applying additional

Since the solvents used with these preservatives are inflammable,
proper -precautions against fire or explosion must be provided where they are
in use. After the treated material has dried thoroughly, however, it should
be similar to untreated wood with respect to fire resistance.

Branding Treated Sash

Since the 1-JP preservatives are practically colorless, it is difficult
and usually impractical to detect their presence in the wood after the sash
have been in service some time. It is very desirable, therefore, that sash
manufacturers place a permanent brand or identification mark on their prod-
ucts, giving the date and some mark to identify the preservative and method
of treatment. This will permit failures to be traced to their sources and
aid in pointing the way to improvements. It will also be of value in iden-
tifying products that give long and satisfactory service.

Report 'To. R919


-reatment for Industrial Buildings

In certain types of industrial buildings, where the requirements for
appearance are not too strict and where it is certain that high decy, resist-
ance is required, the thorough treatment obtainable only by treatment under
pressure may: be necessary to insure the long life that may be demanded. The
purchaser, 'knowing the need for high decay resistance, is prepared to pay
the cost of getting it. He may also wish to use only those preservatives
whose value has been proved by long practical experience. Appreciable quan-
tities 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 roundhouse were creosoted and left un-
painted. The result was considered much more satisfactory than that obtained
with untreated wood or with metal sash.

NSP Wlater Repellents and 17SP Water-repellent Preservatives

NSP water repellents are solutions that penetrate and spread in wood
without causing it to swell and, upon drying, make the wood harder for water
to wet and slower to absorb moisture and consequently swell, without inter-
fering with subsequent painting or varnishin,,. The degree of retardation in
absorption of water and swelling obtained with water repellents is much less
than that attainable with good p-orotective coatings of paint or varnish. The
water repellents do not prevent decay or blue stain; in that connection they
are subject to the limitations already discussed for paints and varnishes.
The solvents used in many water repellents, however, are similar to those
used in 1TP preservatives and the water repellents share with these preserv-
atives the property of spreading readily in wood after the initial penetra-
tion. It is therefore comparatively easy to convert such water repellents
into :TaP water-repellent preservatives by aidi:,-: the necessary proportion of
suitable toxic chemical.

NSP water-repellent preservatives have found considerable use in the
last few years, not only in millwork but in other woodwork and in some mili-
tary equipment and supplies. T-.e extent to which the water-repellent prop-
erty adds to the usefulness of the product, to offset a somewhat ,i,.-er
cost, has not been sufficiently established. For woodwork treated at the
factory but not -painted until it has been installed, the moderate de. -ree of
water repellency obtainable with water-repellent preservatives may furnish
useful protection during< the interval. Some woodwork that usually is left
unpainted and is not fully exposed to the weather but may be subjected to
moisture for brief intervals .,ay profit from the water-repellent property.

Wood Sealers and Preservative Wood Sealers

Wood sealers, which are soiiietimes confused with water repellents, are
essentially thinned varnishes or lacquers. Tin shellac varnish is one of
the oldest wood sealers. Wood sealers resemble water repellents in that
r th products 1-enetrate beneath the surface of wood but the water repellents

Report 17o. R919

continue to spread still further into the wood whereas the wood sealers stay
near the surface, promptly harden there, and, by nearly filling the openings
in the wood cells, render the surface more or less impenetrable by the
liquids in coatings of paint or varnish applied subsequently. The primary
function of a wood sealer is usually to "prime'1 wood so that succeeding,
coats of paint or varnish will be "held out" and form continuous coatings
over the surface. Wood sealers are used also to produce a decorative finish
havin_: iach the same appearance as the old fashioned but very laborious
rubbed linseed oil finish. Such finishes are in rather than on the surface
of the vood.

T"hen wood sealers are applied for the purpose of retarding changes in
moisture content of wood, it has become customary to make two applications
with time enough between for the first application to dry. With water re-
pellents, on the other hand, one application is considered sufficient and,
if more thorough treatment is desired, the time of immersion in the water
repellent is increased or pressure is applied as discussed in the section
entitled "Importance of Good Treatment." The moisture-excluding effective-
ness of a single application of wood sealer is usually less than that of a
good water repellent but a double application of wood sealer is often about
equal to the good water repellents in effectiveness against moisture cove-
ment. The wood sealers do not preserve wood against decay or blue stain.

Preservative wood sealers are wood sealers to which preservative
chemicals have been added. Some of the oil-soluble toxics used in TISP pre-
servatives may be used also in preservative wood sealers provided that the
toxic does not interfere with the drying of the wood sealer. The phenols,
when present in the concentration necessary for preservation, ,may tend to
retard the drying of sealers. Phenyl mercury oleate is less likely to re-
tard drying and is used in a number of sealers now on the market, usually in
a concentration of 1/2 to 1-1/2 percent by weight instead of the minimum of
5 percent considered necessary with the chlorinated phenols.

Since the preservative wood sealers do not penetrate much beneath the
surface of wood, they are not considered so effective as the NSP preserva-
tives or water-repellent preservatives in protecting wood against decay or
blue stain. Where the object is merely to prevent growth of molds on the
surface (mildew), however, the preservative wood sealers may accomplish the
purpose satisfactorily.

Specifications for Sash Treatment

Standard specifications covering acceptable preservatives and methods
of treatment for sash and similar products have been prepared by the iTa-
tional Door manufacturerss' Association and have been in use for some years.

Report To. R919


Use of -'SP Preservatives on Other Products

Although the fore-oing 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, automobile body
parts, refrigerator parts, partitions, office equipment, and furi-iture, when
they are to be used under co?.iitions that require resistance to decay or
insects. Under the conditions that ordinarily prevail in buildings throughh-
out most of the United States, no preservative treatment is required for
floors, partitions, interior finish, lumber, or furniture, but it mI.ay be re-
quired 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 baldcypress in products for
which these woods are suitable. For other products or for other American
woods, or .'!'ere maximum termite and decay resistance is required, preserva-
tives 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 ;.iven 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 of
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, re-
sulting in absorptions of 12 pounds of creosote or more per cubic foot of
wood should give complete decay protection to sash, doors, and similar prod-
ucts throughout their mechanical life or the useful life of the buildi-., in
which they are installed. Creosote treatment, however, is seldo.. acceptable
for s.ccn products.

Thorotugh pressure treatment with reputable water-borne preservatives
should ',ive about the same results as creosoting in situations where the
wood may be damp but will not be exposed to the leac'.ing effect of constant
or frequent contact with free water. Where service conditions favor leach-
ing, water-borne preservatives will be less effective thai creosote.

T..e iTSP preservatives containing not less than 5 percent of a stable
and suitable toxicant have not been in use long enough to have shown by
their performance in actual service just how they compare in effectiveness
with creosote ,ind water-borne preservatives. Laboratory tests and such
limited service tests as are available, however, indicate that the should

Report I'o. R919


thus far available, to expect these preservatives to give satisfactory pro-
tection when they are thoroughly impregnated into wood in substantial quan-

Most sash and similar products are not used under the most severe
service conditions, and consequently they do not require the heav,- treatment
necessary for outdoor structural timbers. Simple immersion for 3 minutes
or longer in NSP 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 stain, more thorough impregnation is
considered necessary for adequate protection.

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

Report ITo. R919

3 1262 08926 9756