PRESERVATIVE TREATMENT OE WINDOW SASH AND OTHER MIELWORK Revised March 1945 No. R919 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin PH3SERVATIV5 TRSATI-'SITT OP WI1TDOW SASH AND OTKSR iilLIWOR X By • P. L. BROWSE, Chemist Kow 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 in- stance 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 manufactured in a year is in the millions. ITo 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 approximate 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 buildings 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.— —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. Weather stripping 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, 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 cooking, 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 though a little more fuel may be required to keep the house warm. Report No. R919 (Revised) -1- 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 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 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. Heart wood 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 de- cay, regardless of the durability of the heartwood. The sapwood of such Report Ho. R919 -2- 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- tive. 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 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 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 only when sapwood is present and then only under damp conditions. Although 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- 2 cay 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 staining cannot be attributed to the wood, but it is an indica- tion 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 neces- sarily the most practical or the most economical) is to make the sash, 2 -Once the faulty condition has been corrected blue- stained sash may be safely repainted provided they are first given time to dry out thoroughly. It may be desirable to remove the old paint before repainting. Report No. R919 -3- frames, or shutters out of naturally durable wood. The heartwood of certain species high in decay resistance can usually he 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, decay 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 long 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 through 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 working of the joints. Moisture that has found access to the interior of painted wood will evaporate more slowly than from unoainted 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 treating to meet the special require- 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 No, 5919 -4- : . - odorless, and paintable - Jogh oftei iged in solox to -'-'. receive a good product that is -• resistant to ieeaj. It is is fax :r:z being a.; simple a; it ; : "._ . r, ~z± :h= ; and . e at " . £ : £ ; ".':_" e f ore cuttj it up and silling it. .; ".£ __£££-£ L." '. £ .£_" ' \ - _ r . t _ ' 7. : r p s orl ": £ sod in the terior of a board 111 also st certain] e~: the board is i lied to i £ d. shape, and und£ :- :. :L£"£ I tic . i eces of aost spc t c - inches I i _ id : : £ . 1 - " _ ii f* i cu 1 7 if press ce— treat in 1 : r "£"""££.' z££r " z " ' " " -r" '.'.-.— ~~ 1? .£ 1 r f Ixili— f the board re not too thi . 3< Lderabl lifficulty is likely to be : it ered 2 :_£_.£_- . sartvood pieces 2 inches thick 01 SI . ■ - _ - - : r - - - i dual j L ece s st bef ore t period )f applj — ion have 1 tage t t coaplel is for there 11 > cut t i ft • then 50l : • - I : ' : 1 - "" : - ' ^~ . Les. 1 - iter into 1 ill nake it : r £^ " _ " " -- : ... . - - - - -.-•:.- - tance real : c 1 jperly treated , i . . ted t dec Sot ixtvood drying. Ehe checking a.-.i lis tort ion - at 1 op in some of t] »1 i parts upon irying ill raste oor€ Lai than a similar ' t oi warping or checking in the rough lumber. Any joints -: at Lnj lue seriously affected by the -a:er and, furthermore, the r_r:a:e of the rood ray be so roughened that resarfacir .-; ill :e resairei. Altogether, t e out- loch for the treatment of assembled sash with preservatives in water solu- tion ices not seea bright but, in sere rase:, it may be found practical. Ireatrea- of the sirisaei parts :e::re assembly would not cause Loose or s-pea .y.ir.'.z zi~. arair raising, warping, checking, a.-.i irying problems would still ":e encountered. Undoubtedly, however, water— borne pre servat i-es can be used to advantage under some conditio] s. . gr Preservative e SSfc [nonswelling, paintable - re servat :-.-es are now available which consist of toxic chemical rarriei in nonaqueous volatile solvent ith or without the further addition of water— repellent ingredients. _\.e.e _ re- rvatives vere level oped :: surmount the iifficulties of using the water- borne ;re:?rT=-i"e3. USE preservatives of suitable sharacter can be applied ~z -.'. after aachinin and surfacing, either just re::^ or i::r: as- bly, without ca sing swellii iistortion, or rou benin of the >od, without req irin careful redrying, without leavin objectionable odor without •_.'-• ei 'ference with subsequent paintin or vamishi .. Various tcxic shenicals have leer, used in ::e servat ive : of this type, Including alphanitronaphthaline, be tana bthol, shlorobetana hthol, chlorort phenylphenol, metallic naphthenates, pentachlorophenol, phenyl mercury oleate, tetrachlorophenol. There may be :::.r: toxics that are as ood 01 better. Phe relative merits of the toxics named have not yet been worked out s tis— factorily, but the chlorinated phenols have found aost extei : Lve use. I!hey are "relieved tc ~:e sufficiently effective >rovide<3 they constitute not less than 5 percent of the treating solution by weight. If the -re ser"ati~e is ssli ir. a r.cncent r=~ ed form to "re ii luted before use, the 5 percent minimum applies - : site solution after it has been diluted. Since "he toxics differ in ::s:, :i:r, :1 rility, = .-. i other proper- ties, it is ~z be expected that, a- knowledge about them increases " r: research and experience, some ill be found rare ie;ir=":le than others. Considerable work in this field is being lone by the Western Pine associa- tion, which has published a number of formula* - re^ir ::r the rare Termatol" for them.— S:r_e sash manuf acturer 3 oufacturers of toxics — ■Fermatol" would be an appropriate general lesignati z:. for all preservatives t] at is not cause wood tc swell luring treatment and leave the ood re:ep- tive of paints or other fiaishes. The s;ll-:l: Per . : ever is leer incorporated in the trade names of 1 commercial product I tot ir names :: other equally suitable products of this oat re. Poor t reason the latirr.al I::r .-arrafactrre: .-.;:: nr 1 : .. ; subcommittee on no- menclature and iefi nit ions a; tentatively recommended the sneral iesi - nation 'HSP, ' ms ain cons ellin , painl lie preservatives. Beport Ho. B91S -6- are also active in this work. Wartime problems have stimulated use of the II SP preservatives for wood products other than sash and millwork. Gradual change and improvement in the preservatives and extension of their use to other fields are to he expected for some years to come. The 1TSP preservatives may well he divided into two types according to the presence or absence of water- repellent ingredients. Those without water repellent consist typically of a solution of toxic in volatile petroleum solvent such as mineral spirits or Stcddard ? s solvent and, in addition, may contain a proportion of less volatile so?. vent, such as fuel oil, to facili- tate spreading of the preservative through the wt?od strucfuire and to prevent "blooming" (collection of crystals of solid toxic on hhs wood surfaces when the solvent evaporates). Other special solvents may be added to improve the solubility of the toxic and to prevent "sludging" (separation of ingredients from solution) while in dip tanks or in storage. Preservatives containing water repellents are discussed further on in this paper under the heading "N5P Water-repellent Preservatives." The degree of effectiveness of the USP preservatives in preventing decay, blue stain, and insect attack has not been sufficiently established. Laboratory experiments have indicated that they should give good protection if the wood is properly impregnated with a substantial quantity. Even the 3-minute immersion treatment, which is now commonly used with sash and simi- lar items, appears to be giving good results in practice. It is believed, therefore, that the use of N"SP preservatives is desirable for millwork that contains sapwood. 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 and limited ex- perience is borne out in general service over long periods of time. In order to choose intelligently among the various NSP 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 market 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 insufficient 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 oresent in the solution, all of which are very important in consider- ing the probable effectiveness of the material. Furthermore, the composi- tion of a secret preservative may be changed at will by the manufacturer or seller, without the knowledge 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 may also make occasional analyses or tests to determine whether the quality remains the same. Enough preserva- tives of known composition are available to make it unnecessary for anyone to purchase secret preservatives. Report LIo, H919 -7- 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 ITational 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 the sash to the frame in the factory and treating after fitting. If the wood is sound to begin with, maintaining a substantial depth of treatment at all surfaces and in all joints will prevent decay of untreated wood that may 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 enroloyed in 1TSP preservatives, it is usually impractical to heat them. The effect of a hot -and- cold bath treatment can be accomplished by heating the wood in a properly controlled kiln and then submerging it and allowing it to cool in a bank 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 pressure. 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. B randin g Trea ted Sash Since the I-TSP preservatives are practially 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 No. R919 -8- Treatment 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 decay 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. IT SEP Water Repellents and ITSP Water-repellent Preservatives ITSP 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 varnishing. The degree of retardation in absorption of water and swelling obtained with water repellents is much less than that attainable with good protective 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 iTSP 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 ITSP water-repellent preservatives by adding the necessary proportion of suitable toxic chemical. ITSP 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. The extent to which the water-repellent prop- erty adds to the usefulness of the prodiict, to offset a somewhat higher cost, has not been sufficiently established. For woodwork treated at the factory but not painted until it has been installed, the moderate degree 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 may profit from the water-repellent property. Wood Sealers and Preservative Wood Sealers Wood sealers, which are sometimes confused with water repellents, are essentially thinned varnishes or lacquers. Thin shellac varnish is one of the oldest wood sealers. Wood sealers resemble water repellents in that both products penetrate beneath the surface of wood, but the water repellents Report No. R919 continue to spread still further into the wood whereas the wood sealers stay- near the surface f 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" 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 having Liuch 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 wood. When wood sealers are applied for the purpose of retarding changes in moisture content of wood, it lias 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 vrater repellent but a double application of wood sealer is often about equal to the good water repellents in effectiveness against moisture move- ment. The wood scalers 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 ITSP 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, ma2 r 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 l/2 to l-l/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 I>TSP preserva- tives or water-repellent preservatives in protecting wood against decay or blue stain. Where the object is merely to prevent grov/th 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 na- tional Door Manufacturers' Association and have been in use for some years. Heport No. R919 -10- Use of 1TSP Preservatives on 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, automobile body parts, refrigerator parts, partitions, office equipment, and furniture, when they are to be used under conditions that require resistance to decay or insects. Under the conditions that ordinarily prevail in buildings through- out most of the United States, no preservative treatment is required for floors, partitions, interior finish, lumber, or furniture, but it may 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 vrell 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 where 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 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 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 building in which they are installed. Creosote treatment, however, is seldo.a acceptable for such products. Thorough pressure treatment with reputable water-borne preservatives should give about the same results as creosoting in situations where the wood may be damp but will not be exposed to the leaching effect of constant or frequent contact with free water. Where service conditions favor leach- ing, water-borne preservatives will be less effective than creosote. The HSP 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 and water-borne preservatives. Laboratory 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 Report Ho. R919 -11- thus far available, to expect these preservatives to give satisfactory pro- tection when they are thoroughly impregnated into wood in substantial quan- tities. Most sash and similar products are not used under the most severe service conditions, and consequently they do not require the heavy treatment necessary for outdoor structural timbers. Simple immersion for 3 minutes or longer in HSP 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. Seoort No. R919 -12- UNIVERSITY OF FLORIDA 3 1262 08926 9756