Glue is what bonds together the veneers or particles or granules or fibres in Plywoods, Particle-boards, Fibreboards and other composite timbers. Some woodworking/construction glues are apparently being manufactured with non-toxic ingredients. Please let the Guide know if you locate a brand which makes this claim1.
FORMALDEHYDE 2 GLUES
Formaldehyde glues are favoured whenever strong structural joins are required, and for bonding wood particles to make composite timber products. Urea formaldehyde amd phenol formaldehyde glues are those most commonly used in composite wood products, such as MDF or particleboard. Other types include melamine, resorcinol and tannin formaldehydes, and epoxies.
Concentrations of formaldehyde in excess of one part per million (ppm), say around 3 to 4 parts per million, can produce eye or throat irritation in most individuals.Worksafe Australia 3 says an emission level of 1 part per million is the safe allowable limit for workers on an 8-hour shift, yet as little as 0.5 ppm can cause throat irritation in more sensitive individuals. Ten parts per million would be intolerably irritating.
Formaldehyde can be smelled in the air at about 3-4 ppm. Breathing air with high concentrations could be carcinogenic 4 (although poor old lab rats have been the only ones to succumb 'officially'). Asthma and skin reactions are possible from contact. Most countries in Western Europe have placed limits on formaldehyde in residential rooms. Manufacturers advise that formaldehyde concentrations in areas without proper ventilation can be significantly reduced by sealing all exposed surfaces and edges with two coats of paint or polyurethane. Urea Formaldehyde is an interior-grade glue, much cheaper than the exterior-grade Resorcinol.
It is important to remember that plywood or chipboard panelling, etc, in a typical Australian home is usually not the only source of formaldehyde fumes: formaldehyde can be found in furniture, wood veneers, lining, shelving, fillers, foams, etc. It is also used as a finish on clothing to make it low-maintenance ('easy care', 'non-iron', etc). Urea formaldehyde was a popular insulating material in the seventies and eighties it could be pumped into wall cavities to help avert the 'energy crisis'. Check your walls in case this invisible source is tripling the levels of formaldehyde in your home.
Resorcinol is a phenol formaldehyde resin, black in colour. It is a marginally less toxic but more expensive alternative to Urea Formaldehyde glue. It performs better under heat-stress than epoxy resin, which is another less commonly used bonding agent for plywood, etc.
Apparently, some architects and builders recommend exterior grade plywood with slightly less gaseous glues for internal building applications. This is probably not a bad idea, considering the effect of formaldehyde at even very low concentrations.
Interior Grade Bonds (ie, types C & D): These are both made from Urea Formaldehyde and are not suitable for structural applications.
Exterior Grade Bonds (ie, types A & B): These are made from phenol formaldehyde (A) and melamine fortified urea formaldehyde (B) and are intended for structural applications. (Melamine is a nitrogen compound.)
Casein glue is a protein derivative of skimmed milk. It is one of the last commonly used natural glues - the use of animal glues derived from hide and bones being now all but obsolete. It is effective at both quite cold and hot temperatures, but is susceptible to moisture and fungal attack. Casein's drying time can be controlled, making it ideal for large glue laminated beams, sandwich panels, flush doors and attachment of laminates 5.
1. A Californian company, Biocomp, manufactures a composite board glued with a a formaldehyde-free resin binder. Compak Strawboard and Ecopanel are likewise manufactured with a formaldehyde-free MDI binder. (See Non Timber Building Materials in the Directory).
2. Formaldehyde:- A colourless, water-soluble, poisonous gas with a pungent odour: used, usually in solution, in the manufacture of synthetic resins and other organic compounds, and as a preservative and disinfectant.
3. See under Consumer Watchdogs/Advocate Groups
4. A "probable human carcinogen", according to the International Agency for Research on Cancer.
5. See chapter 8 of the book Woods in Australia by Keith Bootle.
5. The latin word 'caseus', means 'cheese'. In biochemistry, a white amorphous phosphoprotein formed when milk is curdled by rennet, constituting the basic ingredient of cheese and some plastics or, when precipitated from coagulating milk by acids, used in making paints and glues.