A plywood primer
When building cabinets, most people tend towards plywood over solid wood - it's cheaper, lighter, deals better with moisture and humidity, and comes in big sheets.
Plywood is made by gluing together multiple thin sheets of wood, with grains at right angles to the previous layers. This gives it strength and warp-resistance. The outside layers can be finished to a cabinet-grade finish, or left rough, depending on the application.
No problems so far - it sounds like the perfect material. The problem lies in the glue, which is commonly a formaldehyde-based resin. Formaldehyde is a known carcinogen, and offgases into the atmosphere. Urea-formaldehyde resins, common in 'interior grade' plywood, offgas a great degree; 'exterior grade' plywood uses phenol-formaldehyde - still carcinogenic, but offgases at a lower rate. The phenol-formaldehyde is more expensive, and more waterproof, which is why it's found outdoors. It's also a darker shade of glue, which can affect the color of the plywood.
As people become more aware of the dangers of chemicals, and realize that common materials are releasing deadly toxins into the air around them, industry is slowly responding. Formaldehyde-free plywood is now available.
'Formaldehyde-free' can be interpreted a few different ways, so it's important to look deeply into the manufacturer's claims. There are two basic types of formaldehyde-free plywood:
urea-formaldehyde free: this uses the 'safer' phenol-formaldehyde resins, which offgas at a lower rate. The fact remains that formaldehyde is formaldehyde, and is a carcinogen, whether or not it's more encased in the glue. But this sort of plywood is accepted by US green building codes, and is a big improvement from urea-formaldehyde-containing wood. This category is also referred to as NAUF ('no added urea formaldehyde').
completely formaldehyde free: this kind of plywood uses neither urea-formaldehyde nor phenol-formaldehyde. Different manufacturers use different alternatives - Europly, one of the most commonly available non-formaldehyde plywoods, is available with a soy-based adhesive, called PureBond. PureBond is also available in other panel products from Columbia - check out their site for more info.
A note about your local lumber store: chances are, your local lumber store won't know much about 'green' plywood. You might be lucky, and have a knowledgeable store nearby, but for the most part, you'll get plenty of blank looks and misinformation when talking to the 'experts.' You'll have to do plenty of your own research, find a few options, and look around until you can find what you need.
Some good resources:
- ecohaus.com sells PureBond, but the Europly that they stock is NOT formaldehyde-free - in fact, it's not even urea-formaldehyde free.
- Columbia Forest Products is a major panel goods manufacturer, and seems to be the most widely available of the green products. Their site offers a lot of good information.
Luan is a popular plywood for interior wall panels - it's cheap, and it's thin and flexible (usually found in 1/8th inch). Luan (also spelled as 'luaun') is a 'fake' mahogany grown in SE Asia, and plywood made from it contains high levels of urea-formaldehyde adhesives.
Furthermore, luan harvesting is stripping SE Asia of its old-growth forests at an incredible rate. I recommend avoiding this cheap, damaging product and look for a better alternative.
Masonite is a panel product created by pressing wood fibers with steam and plenty of high pressure. It uses no glue, so it's safe to say that it's non-toxic. It's a good, flexible product for covering walls.