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MDF: The Rest of the Tree

How wood scraps become a smooth, sound building material for the 21st century

<p><em>This Old House</em> TV's Charlestown house project</p>

This Old House TV's Charlestown house project

About 65 to 70 percent of a tree can be used for solid lumber, but what

about the rest? In the past the answer was simple: It was burned or

dumped in landfills. Today more than 95 percent of a harvested tree can

be put to good use thanks in great part to the increased use of

engineered wood products. Among these, medium density fiberboard, or

MDF, has enjoyed remarkable success over recent years. As the MDF

supplier for This Old House TV's Charlestown house, I'm in a good position to tell you

about the material's history.

The material got its start in the United States in 1966, at a plant in

upstate New York. As it became clear that making MDF offered a far

better use of residual wood than disposing of it, production soared.

Today there are some 27 plants in the US and Canada, and more than 100

worldwide. Recently the industry has expanded its use of recovered

materials to include agricultural by-products such as wheat straw and

post-consumer recycled wood.

MDF is typically made from sawdust, planer shavings and other waste that

remains after a tree is milled into lumber. The wood is then cleaned

and mechanically refined in a process that reduces it into fine, uniform

fibers. Excess moisture is removed and an adhesive resin is added to

hold the fibers together. This mix is then formed into a long, thick,

homogeneous mat, which is compressed under intense heat and pressure.

The resulting MDF panel is sanded to a fine, even smoothness, and cut to

the required width and length. Computer-controlled sensors monitor the

entire manufacturing process to measure slight variations that even the

human eye cannot detect. Finished panels are tested for uniformity,

strength and other structural soundness.

MDF is used extensively indoors in furniture, cabinets, doors, mouldings

and flooring. Like other engineered wood products, it has a

distinctively flat, dense surface that holds paint well. It doesn't

move like wood, so its joints stay tight and paint doesn't crack. But

the glory of MDF is its uniformity; it can be machined into every

conceivable shape to create architectural details such as balusters or

mouldings. Unlike real wood, MDF has no knots, grain or warping that

can make intricate woodworking difficult. While solid wood is better

suited to structural applications such as floor joists, MDF tends to be

cheaper than solid wood so it's well suited to interior doors, bookcases

and kitchen cabinets.

In the Charlestown house, the homeowners chose MDF interior doors that

we custom cut to match the house's other large doors. We made and

shipped the doors in only a few days, at a significantly lower cost

than solid wood doors. Once the doors are treated with a faux-wood

grain finish, they will have all of the benefits of MDF with the look

of solid wood.