The wood moisture content in the woodworking

moisture content of the wood vs humidity air graph

The moisture content of the wood is a very important thing in the wood product. The improper moisture content always leads to many problems in the wood product. The controlling of the wood moisture content of the wood in the woodworking industry is very crucial. Theoretically the wood moisture content of the wood at the time of manufacturing and finishing should be approximately the average moisture content it will attain in use or slightly less. The humidity of the air surrounding at the article in use should, therefore govern the extent to which the wood is dried. And then condition in the shop should be maintained at this moisture content level. This is particularly importance in the manufacture of furniture, cabinet o other wooden products in which shrinking and swelling must be reduced to a minimum. While the locally in which the finished article will eventually be used will have some bearing on the relative humidity of the atmosphere.

The effect of the finishing layer to the wood moisture content.

The variation in moisture content is reduced considerably by the finishing coat of paint, varnish, enamel or lacquer. It is common observation that when cracking or checking in of the finish take a place on wood products due to the change of moisture content, the cracking may start form the un coated edge and more severe near the edges toward the center. The finishing layer will wrap the wood, close the pores and grain and make it more stable. Inexpensive coating can be applied to the backs of the furniture or other wooden product to make them equal in moisture resistant to the face surface coating. These coating for back can usually be applied in 1 or 2 coats depending upon the moisture content required.

Any changes of the moisture content of the wood will result in a movement of the wood surface under finish and, if repeated frequently or if of sufficient magnitude, the shrinking and swelling movement will result seriously problem to the finish.  That is way the controlling of the moisture content is very important in the wood product. Watch the moisture content of the wood before finishing, the relative humidity and temperature of the department during the process of manufacture, finishing and storage and the drying time allowed for the evaporation moisture added to the wood by gluing, sponging and staining operation. Keep the wood moisture content to the proper level.

Wood which is too dry at the time of finishing is as bad as wood which is too wet so far as the effect on the finish is concerned. For either case a change in moisture content will result in a movement of wood under the finish. Dry the wood to the proper moisture content for its ultimate uses and keep it at that moisture content during the construction, finishing, storage and use. Then many of the finishing trouble now experienced will be reduced or eliminated entirely.

These are the recommended moisture content for some wood product.

Product                                                                  final MC %

Furniture                                                                     5 - 7

Interior woodwork                                                      6 – 8

Flooring                                                                      5 – 7

Vehicle stock, except wheel and box part                 15 – 18

Vehicle wheel and box parts                                         8

Gun stock                                                                    6 – 8

Aircraft                                                                         8

Army                                                                            12

Outdoor sporting good                                                10

Musical instrument                                                      5 – 7

Miscellaneous outdoor material                                   12