Applied Research -  Laboratory Testing -  Physical

Thickness Swell and Water Absorption

Test Method: Modified ASTM Standards, D 1037 - Standard Methods Of Evaluating the Properties of Wood-Base Fiber and Particle Panel Material, 1989, pp. 167-196.
Water absorption and thickness swell of wood products due to contact with water is a large problem in the construction industry. High wood moisture content increases the susceptibility of the wood to decay and insect damage, and may cause other undesirable physical and mechanical effects. Thickness swell is especially undesirable in construction applications where dimensional stability is required. To reduce, or slow down the absorption of water in wood composites a hydrophobe (water repellent) is added during its manufacture. This test is intended to test the effectiveness of the hydrophobe as well as the overall dimensional stability of the wood composite when submerged in water.
Specimens are measured, weighed and placed under a grid one-inch below the water-line in a water bath maintained at approximately 64F (18C). After two hours and 24 hours the specimens are removed from the water, weighed, and the thickness is measured. The percent change from the original thickness represents the thickness swell, and the percent weight change from the original weight represents the water absorption. Specimens are reconditioned to equilibrium moisture content and measured again to determine the non-recoverable thickness swell.

Specific Gravity, Density, and Moisture Content


Test Method: ASTM Standard: D 2395 - 93, Standard Test Methods for Specific Gravity of Wood and Wood-Base Materials.
Specific gravity and moisture content are two factors having a great affect on the physical and mechanical properties of wood. As such, these variables must always be considered when wood is tested, or used to evaluate the efficacy of an experimental preservative. Wood selection for preservative testing is often determined by the number of growth rings per inch, or by a specific weight range to minimize specific gravity (and density) as a variable. Moisture content is also controlled, either by ovendrying the specimens, or by conditioning them in a climate-controlled room for a specified period of time.

Specific Gravity:The ratio of the ovendry mass of the wood to the weight of the volume of water displaced at a given moisture content.

Density:The weight of a substance divided by its volume.

Moisture Content:The weight of water contained in a substance expressed as a percentage of the mass of the dry weight of the substance.