At present there are many wood drying methods, and some of them are in general commercial use. The problem of whether or not there are some differences in physical and mechanical properties of lumber dried by the several drying methods arises when dried wood is utilized in housing and heavy timber construction. In this paper, a comparison of the physical and mechanical properties of Japanese elm (Ulmus spp.) and grand fir (Abies grandis Lindl.) lumber dried by four popularly-known drying methods is made. These four drying methods are high-frequency electric-power vacuum-drying (E.V.D.), conventional kiln-drying (K.D.), dehumidified drying (D.D.), and air drying (A.D.). Results obtained were as follows: (1) Shrinkage and specific gravity Shrinkage of Japanese elm lumber dried from green to 10 percent moisture content was about 25 percent less in E.V.D. than in K.D. However, a statistical comparison showed that there were no differences in shrinkage for grand fir lumber dried by the four drying methods. The specific gravity was significantly greater in Japanese elm dried by E.V.D. than that by K.D., but for grand fir there were no significant differences in specific gravities by the four drying methods. (2) Mechanical properties The Japanese elm lumber dried by E.V.D. had a slightly smaller average Young's modulus, bending strength, and compression strength. However, the average value of absorbed energy in impact bending was significantly more in lumber dried by E.V.D. than by K.D. A statistical comparison revealed that there were no differences in mechanical properties for grand fir lumber dried by the four drying methods. (3) Equilibrium moisture content and hygroscopicity Lumber dried by K.D. had 0.7 to 1 percent greater equilibrium moisture contents than those dried by E.V.D. and D.D. K.D. dried lumber had a slightly smaller hygroscopicity in cross-sections and quartersawn grain pieces than those dried by other methods. (4) Water absorption Among the four drying methods, water absorption in cross-sections was the most in E.V.D. and the least in K.D. dried samples. K.D. also had the smallest value in quartersawn grain pieces, but there was no clear difference in cross-sections. From these results, it was clear that E.V.D. dried lumber had similar physical and mechanical properties as that dried by D.D. and A.D., but was different from that dried by K.D.
