Composite panels, Part IV: Hardboard
April 6, 2020 | 9:55 am CDT

Product Description

Hardboard was “discovered” by George Mason. According to the legend, Mason was running the press for making wood fiber ceiling tiles, a low density product that relies on intwining of the wood fibers to form a weak panel. However, Mason went to lunch one day and forgot to open the press before he left. When he returned, the heat and pressure had compressed the fiber tile into a dense, dark colored, thin panel. This new panel product was called Masonite.

In furniture and cabinet manufacturing, hardboard is probably only used to add rigidity to a box-like structure. It also provides an inexpensive, thin panel for drawer bottoms. Interior door skins are often hardboard. Probably everyone is familiar with hardboard that has many holes in it, often called peg board. Special hooks are available to provide hangers.

Hardboards are an inexpensive option when high strength is not required. Hardboard is made from wood fibers. The fibers are pressed together in a hot press. The press is so hot that it turns the wood brown. The adhesive that holds the fibers together is lignin, which is one of the main components of wood itself; additional adhesive may be added. Oftentimes, to help excess moisture escape, one side of the press has a screen. This screen pattern shows up on the back side of the panel. The front side is smooth, glossy, uniform textured with a grain pattern.

The typical hardboard panel used in furniture and cabinets is not much thicker than ¼ inch. It must be handled carefully, as this thin piece is not very strong, but is flexible.

There are three basic types of hardboards, standard density, medium density, and oil-tempered. The oil-tempered boards (sometimes just called tempered boards) are impregnated with oil to make them stiffer, harder and somewhat more resistant to scratches and moisture. Try both tempered and un-tempered to see which works best in your application; these two products are considerably different.



          Paints well

          Smooth surface

          Good strength for many applications







Useful Characteristics and Processing Hints

A. Strength. Although quite dense, the un-tempered product used for furniture and cabinets is not exceptionally strong. Tempered boards may be more suitable.

B. Gluing. The smooth, slightly burnished surface can be somewhat difficult to glue. Scuffing the surface helps. However, oftentimes the joint strength required, such as when laminating a paper or fabric product to the face, does not need to be very high.

The backside often is rough enough to be glued, but the joint is not exceptionally strong, partly due to the heat used in manufacturing the panel and partly due to the inherent weakness of this fiber product.

PVA adhesives can be used, but contact cement, CA and PUR might provide a better joint in some cases. As most wood glues were developed for solid wood, some experimentation may be required to find the best adhesive.

C. Fastening with screws, nails and staples. The high density is certainly an issue. when a fastener enters the product without a pilot hole, the fastener pushes the wood out of the way, creating a raised bump around the fastener. Use pilot holes.

Brads can be used as low strength or temporary fasteners while the glue sets. With high density boards, brads may bend too easily.

With screws, use fairly large heads to avoid having the heads pull through easily.

D. Machining. The freshly sawn edges may not be exceptionally sharp; there may be some chip-out. Carbide tips are essential for saws. Saws with more teeth cut better.

Routing a curved edge may make the best edge in many cases.

Sanding of hardboards must be done with very sharp (fresh paper) in order to cut the fibers cleanly. After sanding, clean the surface well. The sanded surface may not be super smooth, as partly-loose fibers often keep popping up. Final sanding after using sizing or a sanding sealer maybe needed.

E. Warping. Unless exposed to liquid water, hardboard is not prone to excessive warping. It is a fairly stable product compared to solid wood. As our industry uses thin panels, we can often fasten them well enough to control warp.

F. Finishing. Tempered boards have a surface that needs to be scuff sanded to develop good finish adhesion. Other hardboards finish with conventional finishes fairly well. Hardboard variations from one manufacturer to the next can create finishing variations. Non-water-base finishes will likely perform better.

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About the author
Gene Wengert

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.