Feeling the Heat

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.

Materials and Methods
Samples of ¾-inch-wide MDF were obtained from the toe kick of a 1980s era kitchen cabinet, while particleboard and melamine-coated particleboard samples were purchased at a Lowe’s home improvement store. Samples were cut into five equal-length pieces (3.5” x 5.5”) and inserted about two inches into cold (36°F), ambient (85°F), heated (165°F) and boiling (207°F) water. Width dimensions were taken at the base and two inches above the base to measure dimensional changes using a micrometer calibrated to 1/1000 of an inch. Temperature measurements were obtained initially and at five- 15-, and 30-minute intervals. Minor adjustments in water temperature were made using ice cubes. An electric stove provided heat. During the test period, samples suspended in ice water, ambient and boiling conditions varied ± 1°F. The samples suspended in 165°F water varied within ± 4°F.

Results
Among the three test materials, the effect of hot-water exposure was most dramatic on the MDF samples (Frame 1). These samples yielded the highest percentage of expansion (350%) following 30 minutes of exposure at 207°F (Table 1). The sample exposed to 165°F water expanded in excess of 100%, and the sample suspended in 85°F water expanded approximately 25%. The sample exposed to 36°F water showed no appreciable expansion.

Both non-coated particleboard (Frame 3) and Melamine–coated particleboard (Frame 2) samples exhibited similar responses at elevated temperatures (Tables 3 and 2). Both samples expanded approximately 100% at 207°F after 30 minutes of exposure. Samples exposed to 165°F water expanded between 35% (non-faced particleboard) and 50% (Melamine-coated particleboard). Both sample types showed no measurable change after 30 minutes of exposure to tap (ambient) water (85°F) and cold water (36°F).

Temperature Profiling
An infrared camera (Flir) was used to examine the vertical extent of elevated temperature in a Melamine-coated particleboard exposed to 120°F water temperature after one week of exposure. The examination revealed that heat from the water bath dissipated from 120°F to less than 90°F within six inches above the source. These measurements indicated that heat dissipation would limit the most severe damage to the lower five to six inches of the composite material.

Discussion
The spacial extent of composite material damage following a hot-water release will vary depending on the initial release temperature, proximity to the hot-water source, volume and duration of the release, ambient temperature inside the structure, temperature setting and operation of the heating, ventilation and air conditioning system, and the thermal conductivity of the flooring and type of foundation (e.g., slab on grade, elevated wood frame).

Water losses are among the most common personal property claims in the United States. Among these claims, water-related claims (e.g., water damage, freezing) comprise approximately 20% of the total, according to Insurance Information Institute statistics. These results indicate that insurance adjusters need training about the behavior of composite materials and their response to water exposure. They should also understand the relationship between water temperature and the extent and duration of damage. We suggest the following considerations when a hot-water release claim occurs.

Dr. Ralph E. Moon, Discipline Director, Building Sciences Dept., HSA, Tampa, Fla., is a frequent speaker at educational seminars for insurance adjusters. Contact Dr. Moon at rmoon@hsa-env.com. Jeff Wilemon, Building Scientist in Tampa, was a multiple-discipline science instructor for 11 years and is currently a consultant with the Building Sciences Dept. Contact Mr. Wilemon at jwilemon@hsa-env.com.