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 AIR-SEASGNING AIRCRAFT iiGtt 
 
 Revised, September 1944 
 
 THIS REPORT IS ONE OE A SERIES ISSUED 
 TO AID THE NATION'S WAR EEEORT 
 
 No. 1366 
 
 UNITED STATES DEPARTMENT OF AGRICULTURE 
 FOREST SERVICE 
 FOREST PRODUCTS LABORATORY 
 Madison, Wisconsin 
 
 In Cooperation with the University of Wisconsin 
 
1XS S3SA80HIN0 AIRCRAFT STOCKl 
 
 It may be necessary to carry a surplus stock of lumber to insure 
 against shortage at the time of manufacture. If the stock is green, advan- 
 e may bo taken of this intermediate period to reduce the moisture content, 
 :eby reducing the time required for kiln drying. 
 
 Lumber properly seasoned should be of uniform moisture content, 
 Straight, free from stain or decay, and without end or surface checks. Ob- 
 -ance of the following rules will help to secure the desired results: 
 
 (a) S*ain prevention: 
 
 If stain is likely to occur, freshly cut lumber containing 
 sapwood should be dipped in or sprayed with an antiseptic solution 
 to protect it against attack by fungi during the air-seasoning 
 period. -2 
 
 (b) Foundations for lumber piles: 
 
 (1) Foundations should be rigid and properly leveled. 
 
 (2) Foundations should be high enough from the ground 
 to allow good circulation. The minimum distance that lumber 
 should be from the ground at the rear of the pile is 18 inches. 
 
 (3) Foundations should slope from front to rear about 
 1 inch to the foot. 
 
 (4) Material for piers is listed in order of durability 
 and should be so selected whenever available: 
 
 Concrete masonry. 
 
 Pressure-creosoted blocks of any species or the un- 
 treated heartwood of baldcypress , redwood, or any of the 
 cedars. 
 
 (When untreated woods are used, all points of 
 contact should be given two coats of hot creosote.) 
 
 • : ograpn is one of a series of reports issued by the Forest Products 
 '- ry to aid the Ration's war effort. Results here- reported are 
 
 preli and may be revised as additional data become available. 
 
 2— 
 
 — rorest Products Laboratory Technical Bote No. 225, "Cause and Prevention 
 
 of Rive Slain in Wood." 1940. Scnef f er , T. C, and Lindgren, R. . 
 "Stains of Saowood and Sapwood Products and Their Control" T J. S. 
 Dept. Arr. Tech. Boll, 714, 123 pp. 
 
 Mineo. "0. 1366 
 
(5) 3eams and stringers should preferably "be of steel, or 
 pressure-creosoted timbers. Untreated durable woods with two coats 
 of hot creosote at points of contact nay be used when neither of 
 the first two is available. 
 
 (6) If existing pile foundations are to be used, they should 
 comply with the requirements given as to height levels and drainage 
 conditions. All weeds, debris, and decayed v/ood and vegetation 
 must be cleared away. Any part of the pile foundation containing 
 decay should be removed or the decayed area cut out. All wood parts 
 should be painted with two coats of hot creosote. 
 
 (c) Air flues: 
 
 The lateral spacing between the edges of boards or of groups 
 of boards totaling 12 to 14 inches in width should be about 4 
 inches, so arranged as to form straight vertical flues in the pile. 
 Where losses from stain are high, the flue width should be increased 
 to about 6 inches. Where surface checking is the principal defect, 
 the flue width should be reduced to 1 or 2 inches. 
 
 (d) Stickers: 
 
 (l) All stickers must be sound, thoroughly dry, free from 
 stain, and of uniform thickness. 
 
 beam. 
 
 (2) Each tier of stickers must be aligned and rest on a 
 
 (o) Stickers for 4/4-inch lumber shall be of nominal inch 
 stoc$ or thicker and not more than 4 inches wide. For thicker lum- 
 ber of random length, stickers should be at least 1-1/2 inches thick, 
 for greater stiffness and strength, and should not be more than 4 
 inches wide. 
 
 (4) Stickers should overlap the ends of the boards at least l/2 
 inch to reduce end checking. 
 
 (0) Stickers should not be more than 2 feet apart for hard- 
 woods up to s/4 inches in thickness. For thicker hardwoods and all 
 softwoods, the spacing should be equivalent to five rows of stickers 
 for 16-foot stock. 
 
 (5) Aircraft stock should never be self-stickered. 
 (e) Placing of lumber: 
 
 (1) Piles should be erected of boards of equal length wherever 
 practicable. 
 
 1366 -2- 
 
(2) 3ox piling should "be used for mixed lengths. In this sys- 
 tem, the longest stick is piled in the outer rov/s and short lengths 
 within the nile, with one end of a "board at one end of the pile, and 
 one end of the adjacent "board at the opposite end of the pile. In each 
 succeeding layer, the outside ends of boards should be kept immediately 
 over the ends of those below. 
 
 (3) Each layer should be composed of boards of the same thick- 
 ness. 
 
 (4) The pile should have a forward pitch of 1 inch for cacn foot 
 of height and a slope from front to rear of 1 inch for each foot of 
 length. 
 
 (5) Harrow piles are desired for stock that will withstand rapid 
 drying. Vide piles are desired for stock that may check and honeycomb. 
 Common pile widths range from 5 to 16 feet. 
 
 (6) Lateral space "between piles should be about 4 feet. The 
 distance "between the rear of one pile and the front of the next should 
 be about 8 feet. 
 
 (f) End coatings: 
 
 Wood dries more rapidly from the end grain than from the side 
 grain and is apt to check and split during seasoning unless end drying 
 is retarded "by means of end coatings. Either cold or hot coatings can 
 "be used. 
 
 One of the best cold coatings developed at the Forest Products 
 Laboratory la an inexpensive hardened gloss oil thickened with barytes 
 and magnesium silicate. 
 
 The manufacture of hardened gloss oil involves technical opera- 
 tions of such exactness that it should be made only by a commercial 
 paint manufacturer. A hardened gloss oil suitable for end coating and 
 made in accordance with the following formula should be specified: 
 
 6 to 8 parts, by weight, hydrated lime. 
 
 100 parts, by weight, rosin. 
 
 57,5 parts, by weight, mineral spirits. 
 
 To 100 parts by weight of this gloss oil, add 25 parts barytes 
 and 25 part3 magnesium silicate. If a black coating is desired, one 
 or two parts of lampblack may be added. Because gloss oil so 
 thickened tends to become pasty after standing, the user should mix 
 small quantities as needed. 
 
 Paraffin is a satisfactory end coating for stock during air 
 seasoning, but it melts at kiln temperatures. 
 
 1366 _3_ 
 
The following hot coatings are particularly satisfactory for 
 wood that is to he kiln dried after air seasoning: 
 
 (1) Coal-tar pitches or asphalts with melting points between 
 195° and 213° F. 
 
 (2) Mixtures of such coal-tar pitches and asphalts. (Example 
 100 parts "by weight of 213° and 40 parts of 155° F. coal-tar pitch 
 plus 25 parts of 220° asphalt.) 
 
 (3) Rosin and lampblack (lOO parts by weight of rosin to 7 
 parts of lampblack). 
 
 (4) Any mixture of high-melting-point pitches and rosin. 
 
 When end coatings chip or shear off, a fresh coating should 
 be applied. 
 
 (g) Covering: 
 
 All material should be under cover either in an open shed or 
 with roofs over individual piles. One satisfactory type of pile roof con- 
 sists of two layers of low-grade boards. Those in the upper layer should 
 be staggered with respect to those in the lower layer. 
 
 (1) A minimum front height of 6 inches above the lumber, 
 with a slope at least 1 inch to the foot, should be required. 
 
 (2) The ends and the sides should project sufficiently to 
 prevent snow and rain from beating into the lumber piles. 
 
 (3) The roof should be securely fastened to the pile, 
 (h) Site: 
 
 The yard should be well drained and kept free of weeds and 
 debris. 
 
 1366 -4-