THE GLUING OP WOOD 61 
1. Open glue joints — Continued. 
B. Improperly dried or conditioned lumber, as a result of — 
(1) Too high or too low moisture content (p. 14). 
(2) Moisture contents not uniform (p. 15). 
C. Improper design, as a result of — 
(1) Thick plies (plywood construction) with the grain at right 
angles (p. 54). 
(2) End-grain joints not properly reinforced (p. 59). 
2. Blisters. Some of the causes are the following: 
A. Uneven thickness of stock (p. 16). 
B. Incomplete contact, as a result of irregular spread of glue (p. 23). 
C. Poor cauls (p. 26). 
D. Too short pressing time (p. 27). 
E. Steam pockets (in hot pressing) (p. 29). 
F. Causes listed under 1. 
3. Warping. Some of the causes are the following: 
A. Unbalanced construction, as a result of — 
(1) Corresponding plies not parallel or at right angles to adjacent 
plies (p. 53). 
(2) Corresponding plies of unequal thickness, sanding, shrinkage, 
density, or moisture content (pp. 54 to 55) . 
B. Cross-grained or decayed wood in crossbands or cores (pp. 55 and 56). 
C. Gluing together pieces of unequal or incorrect moisture content 
(p. 58). 
D. Improper drying after gluing, as a result of — 
(1) Drying conditions too severe (p. 29). 
(2) Final moisture content too low (p. 32). 
(3) Stickers improperly placed or insufficient in number. 
(4) Unequal or incomplete drying. 
E. Bending in press and clamps (p. 27). 
F. Uneven moisture changes through finish on face and back. 
4. Surface defects, such as: 
A. Checks, as a result of — 
(1) Finishing before wood has dried to proper moisture content. 
(2) Wood glued at too high a moisture content (p. 14) . 
(3) Too much moisture added in gluing (p. 15). 
(4) Drying conditions too severe (p. 29). 
(5) Internal stresses. 
(6) Improper construction, due to face plies and adjacent under- 
plies parallel. 
(7) Assembly time too long (p. 38). 
(8) Poorly cut veneer (p. 19). 
B. Sunken joints, as a result of surfacing before glue moisture is dried 
out or distributed (p. 31). 
C. Corrugated appearance, as a result of — 
(1) Planer marks on core or crossband (p. 17). 
(2) Using cores or crossbands of very contrasted grain (p. 55). 
(3) Uneven moisture content in core lumber before gluing 
(p. 15). 
D. Uneven spots, as a result of — 
(1) Knots, limb markings, or bruises in core or crossbands 
(p. 55). 
(2) Open joints or laps in crossbands. 
(3) Uneven spread of thick glue under faces or crossbands. 
(4) Blisters (see 2). 
E. Staining, as a result of — 
(1) Alkaline glues (Table 1 and p. 49). 
(a) Veneer glued too wet (p. 16). 
(b) Left in clamps too long (p. 29). 
(2) Use of too thin face veneers with dark-colored glue (p. 49) . 
(3) Use of wood which was discolored before gluing. 
(4) Too high temperatures in pressing panels. 
