Water losses lead personal property claims in the U.S., but are they as well understood as they are widely prevalent? A recent study shows that when medium density fiberboard (MDF), non-faced particleboard and Melamine (faced particleboard) are exposed to water, dramatic dimensional changes occur at water temperatures above 85°F. The swollen appearance of these wood composite materials was consistent with long-term exposure to moisture, although the exposure period was only 30 minutes. The test results underscore the importance of understanding the effects of elevated water temperatures on composite wood materials used in cabinetry, furniture and trim when supporting decisions of duration of loss.

Medium density fiberboard and particleboard are among several composite materials that are manufactured by spraying dry wood particles with a binder resin and bonding them together with pressure and heat. The U.S. Department of Agriculture applies the term “composite” to any wood material that is bonded together with adhesives.

Wood composite materials are made by thermosetting or heat-curing a resin or adhesive to hold wood fibers together. The most common resin-binder systems used are phenol-formaldehyde, urea-formaldehyde and Melamine-formaldehyde, according to the USDA.

Phenol-formaldehyde (PF) resins are used in the manufacture of products requiring durability in an exterior environment, such as oriented strand board (OSB), siding and plywood. Urea-formaldehyde (UF) resins are used in products where dimensional uniformity and surface smoothness is important. Products that use UF resins are intended for interior applications. Melamine-formaldehyde (MF) resins are used for decorative laminates (desks, cabinets, vanities) and paper applications. UF and MF resins were used in this study.

As defined by the USDA, the term fiberboard includes hardboards, medium density fiberboard (MDF) and insulation board. Fiberboard is distinct from particleboard because, during its manufacture, long strands of wood fiber bundles are intentionally created with the intent of using the inherent strength of cellulose fibers. Fiberboard is preferred for furniture and cabinetry construction because fiberboard is easily machined and finishes to a uniform surface that is excellent for paint and decorative overlays. Because composite materials are hygroscopic, MDF swells irreversibly when it contacts water, the USDA found.

Particleboard is manufactured from sawdust, shavings and wood mill wastes. Particleboard is typically made in three layers, with the exterior faces consisting of fine wood particulates and the interior layer made of coarser materials, according to the USDA. Particleboard is also prone to expansion and discoloration when exposed to water. It is rarely used outdoors or in places with high levels of moisture. Melamine-coated particleboard is commonly used in cabinetry and furniture.

Three factors—spring-back, adhesive deterioration, and shrinking and swelling stresses—have been found to contribute to composite wood deterioration when it encounters changes in moisture content, according to the Forest Products Journal. Spring-back refers to the recovery of materials after compression during manufacturing. The degree of spring-back reflects the amount and durability of the binder adhesive. Shrinking and swelling represent cyclic exposure to moisture and the physical separations that occur as a result of movement.