MDF goes on a diet

The smooth, dead-flat faces and void-free interior of medium-density fiberboard (MDF) make it ideal for jigs, as a substrate under veneer or laminate, and for building utility cabinets. But if you've struggled to lift a 90-pound sheet, you need to get acquainted with this sheet-good's siblings: lightweight and ultralightweight MDF (L-MDF and U-MDF).

The reason lies in the resin

Like their beefier big brother, L-MDF and U-MDF are made from wood fibers, waxes, and resins fused under pressure and heat. But because less resin is used, the panels weigh significantly less than standard MDF.

However, the reduced weight comes with trade-offs. L-MDF and U-MDF scratch, chip, and ding easily. Horizontal spans sag significantly more than standard MDF, photo below, and they have less screw-holding strength [chart, below].

Lightweight MDF.jpg

MDF weight chart

Also, you'll pay slightly more for L-MDF and U-MDF than for MDF. Distribution has been primarily on the coasts, making these items a special order in other regions.

Make exposed MDF edges more attractive:

Countersink to prevent mushrooms

The lower density of L-MDF and U-MDF make them easier to cut than the standard stuff. But the lighter versions still dull cutting edges and create clouds of fine dust, so always wear a respirator and eye protection. When fastening any type of MDF, drill and countersink pilot holes to prevent mushrooming [Photos right].

Tear-out around screws
Even with a pilot hole, driving a screw into MDF will raise fibers around the screwhead and blow out chips on the bottom face.

2 boards screw going threw on with a hole in the other
To prevent this, drill countersinks on both faces of the through pilot hole, and on the mating surface of the mating piece. This provides relief for any forced-out material, allowing the parts to seat fully.

  • For #6 screw: 564 "
  • For #8 screw: 332 "
  • For #10 screw: 764 "


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