What Is Hardyboard Siding?

What It's Made Of

Hardboard siding is not made of regular wood. Rather, it is a combination of wood filler, resin and wax used to create a composite material. It is sold in panels as well as boards. The finish can be plain, or the manufacturer can finish the panels to look like real wood. There is some confusion with hardboard siding, mainly because a manufacturer named Masonite makes this panel. This name has led to the confusion that hardboard is a concrete or mortar-based product, when it is actually made of wood.

The manufacturing process causes the wood fibers to release a compound known as "lignin." This acts as a natural adhesive, binding the fibers and resin together. It also prevents wood rot. This type of siding is known to be more resistant to decay than other siding materials. Its uniform appearance and relatively low cost, coupled with its durability, have made it a favorite among contractors, especially in larger developments.

Although it is resistant to rot and decay, if hardboard is exposed to the elements before installation, or is exposed to masonry products, it eventually will begin to decay. Flexible caulk must be used with it, instead of hard caulk, and a vapor barrier is necessary between the insulation of the home and this siding. Failing to follow these procedures during installation can result in a very large mess and siding that needs to be replaced.

Unlike other forms of siding, hardboard requires a few different installation techniques. For example, the nails used must go through the framing studs at least 1 1/2 inches and they cannot be countersunk. The spacing between nails cannot exceed 16 inches. All field edges must be painted prior to installation and must be free of mold and dirt to ensure that this material does not get trapped next to hardboard, creating the potential for future damage. Hardboard siding should never be left on the ground for extended periods before installation or it will begin to rot.