Comparing the Relative Effectiveness of WaterRepelling and Retarding Solutions in Wood A Laboratory Method ERNEST E. HUBERT, Western Pine Association, Portland, Ore.
sapwood of even texture, free of blemishes and defects, and from them cut test pieces 0.625-inch (1.6 cm.) thick, 4 inches (10.16 cm.) wide, and 8 inches (20.32 cm.) long, with the flat rain in the 4-inch (10-cm.) face and these two faces s a n d e l The longitudinal grain should follow and parallel the long axis of each piece. The test piece and its control piece should be taken adjacent to each other end to end and from the same board to eliminate certain variables. The range in specific gravity of the test pieces shall be within 0.35 to 0.40 and the difference in weight between any two matched test pieces shall be within 5 per cent. 2. CONDITIONING OF PIECES.Place the numbered treated and control pieces in a conditioning chamber reguhted to maintain 12 * 0.5 per cent moisture content in the wood a t 26.7" C. (80°F.) when constant weight is reached. Wei h each piece and record as A . Weights in all cases shall be witain 0.1 gram. 3. TREATmNT. After weighing, submerge the test pieces vertically, the 0.625 X 8 inch (1.6 X 20.32 cm.) face parallel to the bottom of the container, and the upper face 3 inches (7.5 cm.) below the surface of the water-repellent mixture, prepared according to the manufacturer's direction, at 26.7" C. (80" F.) for 3 minutes. Weigh soon after draining and record weight as B . 4. RECONDITIOSING. After exposing to the air for 30 days, place the test ieces, including 4 untreated reference pieces, in conditioning clamber as in Item 2 until constant weight is reached. When conditioned, measure to third decimal place across tangential or flat-grain face and record as C . Weigh and record as D. Weigh the reference ieces, then oven-dry a t 102" C. and record n-eight. Compute &e average moisture content per cent. 5 . TESTS. Use 10 treated and 10 untreated pieces matched in pairs as indicated in Item 1. a. Expose them to 97to 98 per cent relative humidity at 26.7". (80' F.). Measure across tangential face and weigh after 0, 4, 8, and 24 hours and at 24-hour intervals for 7 or more days. Record measurements as F , and record weights as G. b. Gsing a second set of conditioned pieces, submerge them Lvith the 0.625 X 4 inch faces parallel to the bottom of the container in a constant-temperature (26.7" C.) water bath, the upper 0.625-inch faces exactly 1 inch (2.54 cm.) below the water surface. Measure and weigh a t intervals as in a. Record measurements as F and weights as G. Make all measurements at the mid-point of the 8-inch (20.32cm.) dimension and along the 4-inch (10.16-cm.) dimension. Record the average of two measurements when using calipers and a single measurement when using a dial gage board. Before each weighing, wipe the test piece clean of surface moisture. Place the test pieces in the same position each time they are measured. 6. COMPUTATIONS.
The method described in this article is a correlation of the laboratory technique developed by the following members of the Preservative Standards Advisory Committee of the National Door Manufacturers Association and was prepared for publication by the chairman: S. 0. Hall, National Door Rlanufacturers Association; Geo. 31. Hunt, Roy H. Baechler, C. Audrey Richards, and Theo. C. Scheffer, Forest Products Laboratory; Ira HatBeld, Monsanto Chemical Co.; Dale Chapman, A. D. Chapman and Co., Inc.; Gardner Garlick and William Bradley, Protection Products Rlanufacturing Co.; J. B. Mellecker, Curtis Companies, Inc.; D. K. Ballman, Dow Chemical Co.; F. H. Kaufert, E. I. du Pont de Nemours & Co., Inc.; J. 0. Frank, Morgan Co.; Henry Schmitz, University of Minnesota; and Ernest E. Hubert, Western Pine Association, chairman.
T
HE increasing demand by the woodworking industry for
water-repellent or retardant solutions, which are to some extent effective in shedding water and in retarding the rate a t which moisture is absorbed by the wood, has presented a new problem to the technical workers n-ho are engaged in the testing of such solutions. As soon as attempts were made by individual testing laboratories to evaluate the relative effectiveness of proprietary water-repellent solutions i t was found that no standard or near-standard method of testing was available. This situation was called to the attention of the S . D. 11.A. Advisory Committee ( I ) in 1938, and a t the meeting of this Committee a t Madison, ST'is., on N a y 16 and 17, 1939, a tentative laboratory method of testing the relative effectiveness of water-repelling and retarding solutions was agreed upon. This method, like the one used in testing the toxicity of preservatives in n-ood, represents the more desirable steps in technique taken from the methods developed and used during the past 12 months by individual members of the committee. It was recognized a t the bladison meeting that water-repellent solutions do not make wood immune to moisture and dimension changes and that they do not protect wood appreciably when exposed continuously for several weeks or months to liquid water or to high humidities. T h a t they have some protective value under certain conditions was readily admitted and i t was agreed that a start should be made in evaluating them for use on millwork products. While the committee was unable to reach complete agreement as t o the degree of effectiveness required in a n acceptable water-repelling or retarding treatment, it came as near to an understanding of the problem as present k n o d edge on the subject permitted. As research and experience add nevi data on the subject and comparisons are made with the results obtained by individual workers all using the same laboratory method of testing, a better basis for evaluating water repellents may be developed. Meanwhile the approved method is submitted for trial and improvement.
B
-A -C
= amount of water-repellent absorbed = amount of water-repellent retained after conditioning = Increase in width due t o swelling during test
D - A F SI
- Sa
SI
6' - D
w1 -
Wl
X 100 = % effectiveness in retarding swelling =
W ,amount
of water absorbed during te:it
Wa X 100 = % effectiveness in retarding water absorption
SI, WI = control pieces S:, ma = treated pieces
Since the effectiveness of the above tests depends to a considerable extent upon the wood test pieces selected for use, i t is important that these pieces should contain no heartwood. I n selecting the sapwood material the color indicator described in the article presenting a method for testing toxicity of wood preservatives should be used (1).
Tentative Method
Literature Cited
1. TESTPIECES. Select pieces 6 feet (2 meters) or longer, surfaced on four sides, of kiln-dried, flat-grain Ponderosa pine
(1) Hubert, E. E.,IND.ENO.CHEM.,Anal. Ed..12, 139-41 (1940).
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