The Preservative Treatment of Millwork
commonly found attacking millwork. Resistance to termites may be desirable in regions where the products may be exposed to them.
Penetration Tests
ERNEST E. HUBERT Western Pine Association, Portland, Ore.
0
ITE of several projects conducted in the Research Labora-
' tory of the Western Pine Association in 1935 was the
study of the control of stain and decay in finished wood products, such as sash, doors, frames, porch columns, and general millwork, which are ordinarily exposed to considerable moisture during service. I t was evident from the outset that this problem presented several new angles and that it could not be solved by simply recommending the use of all heartwood stock for the most vulnerable portions of the wood product concerned, because of the inability to make such segregation in the operations and to procure it in adequate volume. The fact that all woods are in some degree susceptible to decay, and that the use requirements of woods selected for these products play a n important part, made it necessary to find simple and inexpensive means of protecting these species of wood which, during the past decades, have been repeatedly selected as fulfilling these use requirements most satisfactorily.
As the first step in the study of preservatives suitable for dipping sash, it was necessary to gather a large number of samples of petroleum products of known specifications preparatory to making tests of their ability to penetrate wood. A number of companies in various parts of the United States furnished samples of their products. These solvent carriers were colorless, volatile compounds, most of them with flash points above 100" F. In all, 60 solvents and 18 proprietary sash compounds were run through the penetration tests. Blocks of wood, 1.375 X 2 inches and 4 inches long, were cut from ponderosa pine, Idaho white pine, and sugar pine, the sapwood and heartwood being kept separate. The blocks, after numbering, were dipped in the solvent which was colored red by dissolving in it a quantity of oil-soluble aniline dye (5486, Nyanza Color and Chemical Co.). Three blocks of sapwood and three blocks of heartwood of each species of wood were dipped for 20 seconds in the solution which had previously been warmed to 80' to 85' F. The blocks were not heated but were dipped cold. After a period of drying, each block was split in halves in the direction of the grain and the average depth of complete penetration and the average depth of streak penetration longitudinally were recorded in inches and fractions.
I n the study of the control of stain and decay in finished wood products which are ordinarily exposed to considerable moisture during service, 25 chemicals and 18 proprietary wood preservatives were evaluated for toxicity, volatility, leaching by water, and ten other factors included in the requirements for an effective preservative. Four of the most promising toxicants-pentachlorophenol, O-phenylphenol, 2-chloro-o-phenylphenol, and tetrachlorophenol-were selected and are recommended for use in the treatment of millwork products.
Protecting Millwork The problem of protecting millwork against stain, decay, shrinking, and swelling is primarily concerned with keeping moisture out of wood and of poisoning the wood against fungi by the use of preservatives. Since the absence of moisture will prevent such changes in wood, its exclusion, while not always possible, is desirable. However, should moisture pass the barriers set up against it, a toxic element is also needed to prevent the stain and decay organisms from developing. Sufficient work has already been done (6, 6) on this problem to explain these relationships and to recommend certain methods of protective treatment. Faulty joints, poor painting jobs, and the unfinished edges of doors, windows, and frames are mainly responsible for the entrance of decay and in most cases for the development of stains, which may appear as blue to black discolorations beneath or upon coats of paint and other finishes. Cracking or flaking of good paint jobs, due to raised grain or to the openings into the wood made in fastening the hardware fixtures, is occasionally responsible for failures. Owing to the need for low cost, avoidance of reseasoning, and simplicity of treatment, any effective mixture must contain a cheap toxicant dissolved in a n oily carrier. The carrier should be a colorless, rapid-penetrating liquid which evaporates quickly from the wood, leaving a paintable surface. The mixture should possess no unpleasant odor, should be noncorrosive to iron, should possess a high flash point, and should not be excessively poisonous or harmful to human beings. The toxicant should show a high degree of permanency in the wood, remaining toxic in it for a, long period of time, and should be toxic to the decay and stain organisms
Complete penetration represented a uniform diffusion of the solution throughout the central area of the test piece while streak penetrations represented the advancing streaks of solution beyond. Wherever the amount was measurable, the average penetration radially and tangentially was also recorded. Measurements for each set of three blocks were averaged and these figures were used to plot graphs which showed the relative penetration values of the liquids tested. It was found that the longitudinal measurements were the most important, since little appreciable radial and tangential penetration was noted. In all cases the sapwood of each species was penetrated, on the average, more readily than the heartwood, and of the sapwood samples sugar pine was most readily penetrated, Idaho white pine next, and ponderosa pine third. 1241
INDIJSTRIAI, AND ENGINEERING CHEMISTKY
1242
VOI.. 30. NO. 11
Penetration of the wood by the petroleum solvents was first accomplished by capillary action along the vertical resin ducts, the solubility of the resin in the solvents aiding considerably. Tho best solvents penetrated sugar pine aapwuod pieces 2 inches in length in 3 to 7 seconds, the red liquid first appearing on the upper cross-sectional area in the form of small round red spots (Figure 1). Further study showed these noints to be the openinxs of resin ducts which were not
The resultant preservative has a high flash point, produces no sludge, shows very little or no bloom upon the treated wood,
F , ~ ~ pENETaTIoNmD ~ ~ ~ : s~~~~~~~ o F ~ o l V E N T cARaIEn
final preservative is greatly reduced. In all, more than 950 tests were made in determining the penetration, spread values, and characteristics of solvent carriers and of proprietary sash preservatives. While the data on longitudinal, radial, and tangential w e tretion of wood gave a good index of the penetration values of the liquids tested, they do not represent positive values, 8,s wood is in itself variable, and measurements of this kind expressed in averages need frequent revision. Many more tests are needed in order to obtain more accurate Yet it is believed that these tests are sufficiently accurate as a basis to select the best solvent carriers, t,o segregate the spreaders from the more rapid Penetrants, and to gain Some of the penetration qualities of the propl.ietarY compounds. The Eoilo'ving penetrants spreaders have been tested by the method described and by nleans of the 2-inch block method; and approved for use in millwork prcservat.ives.
C. Treaied block split open. Note penetration in narrow stiesks along
S'enctrants StFUli~Ol
Standard Stoddsrd solvent sursso1 .4rnaao apeeiai solvent Thinner N o . 7 Paint base tliinner Toledo or Yale apceial Stod-Sol or Apcv 126 vnrsoi Jhell Stoddsid advent Spresders Keroseae or No. 9 refined m l
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