Standard Test Methods for MOISTURE CONTENT OF WOOD
|Publication Date:||29 April 1974|
These methods cover the determination of the moisture content of wood. The methods provide a means whereby producers, fabricators, processors, and users of wood and wood products can facilitate inspection for adherence to moisture quality-control specifications. The requirements, advantages, and limitations of the different methods are outlined.
The methods described are commonly used in research and by the producing industries to ascertain the amount of moisture present in specific specimens representing the lot or on samples tested with the electronic moisture meters. These different methods are not equally suitable for moisture content determinations in any given case; therefore, it is important to select the one that is best for the intended application and a specific method may be specified. If these methods are referenced with out designation of the specific method to be used, it shall be assumed that all methods are equally acceptable and that the choice will be made by the party responsible for the moisture-content determination. The following guide to the advantages and limitations of the various methods will assist in making the proper choice:
Method A-Oven-Drying Method-The moisture content is calculated from weight values obtained before and after drying a representative specimen of wood in an oven. This has been the most universally accepted method for determining moisture content in research, in wood-seasoning operations such as air drying, predrying, and kilin drying, in moisture content control techniques in processing in wood-working factories. Its limitations are that it is a destructive test in that the samples representing the lot must be cut to produce the specimens; it takes several hours to make an accurate analysis; and accuracy is limited if the wood contains an appreciable amount of voiatile extractives, or if the wood has been impregnated with either volatile or nonvolatile chemicals.
Method B-Electronic Moisture Meter Method-Moisture content control often requires a rapid, nondestructive and reliable means of inspection for moisture content, and this requirement is met most conveniently by electronic moisture meters. Reliable results, however, can be obtained with moisture meters only when they are correctly used. A standard procedure should be established and accepted by users of these instruments and the method presented herein is intended to provide a uniform procedure for the use of electronic moisture meters for wood so that determinations made with them may be reliable and strictly comparable.
Merhod C-Distillation Method-The distillation method is destructive as is the oven-dry method. The procedure for selecting the specimen for analysis is the same as for the oven-drying method. The method is used when the wood contains volatiles other than water, such as pitch or oil-type preservatives, or has been impregnated with other chemicals that are soluble in toluene. The method generally consists of distilling the water from the fractured specimen along with a liquid that is immiscible with water such as toluene, catching the water in a trap and measuring its volume, and calculating the moisture content. The time required for the test method is often less than 2 h. This method also may be used to determine the quantity of any volatile material such as sote in the wood specimen.
Method D-Hygrometric Method-The hygrometric method is also destructive as are the oven-drying and distillation methods. However, it is a fairly rapid method for obtaining moisture content estimates on wood samples that have been treated with preservatives or other chemicals. The method is limited to wood having a moisture content less than the fiber-saturation point.