Manufactured wood products such as plywood, oriented strand board and medium density fiber board, are made from wood layers, chips or flakes which are held together with formaldehyde-based glues or resins.
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- Phenol-formaldehyde (PF)
- Urea-formaldehyde (UF).
Its water resistant properties make phenol-formaldehyde glue more effective for production of exterior wood materials. Urea-formaldehyde glue, cheaper and less tolerant of excessive moisture, is most often used for interior materials including wall paneling, flooring and cabinetry.
Of the two resins, UF glue out-gasses considerably more formaldehyde than the PF glue and can be a major source of indoor pollution.
Furniture Grade vs. Construction Grade Materials
Manufactured wood products meant for interior spaces are usually considered furniture-grade materials. Products intended for exterior use are generally known as construction-grade. Materials labeled as furniture-grade equates to a confirmation that UF resins were used in their manufacture. These products will often have a warning label stamped on the back similar to the following:
“Warning: This product is manufactured with a urea-formaldehyde resin and will release small quantities of formaldehyde. Formaldehyde levels in the indoor air can cause temporary eye and respiratory irritation and may aggravate respiratory conditions or allergies. Ventilation will reduce indoor formaldehyde levels.”
In its natural state, softwood lumber emits a tiny amount of formaldehyde. While PF-glued products typically emit 10 times the formaldehyde outgassed by softwood, UF resins can release at least 100 times more formaldehyde than the natural wood.
A typical particle-board subfloor made with UF glue can release enough formaldehyde to result in a 0.3 ppm concentration of formaldehyde in a room. For healthy people who are not bothered by formaldehyde, the levels in softwood lumber and PF glue are usually not considered a serious health problem.
UF glue, on the other hand, has been implicated is causing people to become hypersensitive; a good reason for healthy people and sensitive people to avoid UF glues altogether.
Formaldehyde Outgassing Rates
The outgassing of formaldehyde is measured in units of micrograms per square meter per hour (µg/m2/hr). Following are the ranges that have actually been measured in different products in various studies.
Particleboard(UF glue) 100-2,000 µg/m2/hr
(UF glue) 210-2,300 µg/m2/hr
(UF glue) 7-1700 µg/m2/hr
Furniture-grade plywood w/ vinyl or laminate surface
(UF glue) 3-300 µg/m2/hr
(PF glue) 2-83 µg/m2/hr
The outgassing rates for both glues decrease with time. In fact, the half-life of the out-gassing is usually between 3-5 years. This means that during the first 3-5 year period, half of the formaldehyde will have dissipated, and during the second 3-5 year period, half of the remainder will dissipate, and so on.
The actual emission rate of a particular product containing either PF or UF glue depends on several factors (e.g. age or quality of the resin, additives such as formaldehyde scavengers, application methods, mixing, etc.). Manufactured wood products outgas much faster in hot, humid climates than in cool, dry locales.
And while PF glue is generally less potent than UF glue, it’s important to know that there is a wide variation between products. Some strong PF products can be as potent as weaker UF products; and even low formaldehyde emissions from PF resins have the potential to combine with small amounts of the many other indoor air pollutants.
With these factors in mind, a conservative recommendation would be to avoid manufactured wood products containing either PF or UF glue.
To their credit, the wood-products industry has reduced formaldehyde emissions considerably over the years on a voluntary basis. Yet, the amount of formaldehyde released from products containing UF glue is still too high and their use should be avoided in a healthy house.
The Healthy House, 4th edition
John Bower, Author
Copyright ©The Healthy House Institute
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