Hardboard is a composite wood product used in construction and woodworking. It is typically sold in 4' by 8' (1.2 to 2.4 m) sheets, and can range from 1/4" to 1" (6.35 to 25.4 mm) in thickness. While it is similar in appearance to plywood or particleboard, hardboard is actually constructed quite differently from these products. It is made from fine wood fibers that are compacted under high levels of heat and pressure to form a very dense, hard wooden sheet. Due to the extreme heat and pressure levels, there is usually no need to use adhesives or binding agents to hold the wood fibers together.
Builders can choose from three basic types of hardboard sheets. Service-grade units are the most affordable, but are also the least dense. Standard-grade boards are the most widely used, and tend to be smoother and stronger than service-grade products. Tempered boards are the most strong and durable type of hardboard. They are coated with linseed oil and heated to increase their moisture-resistance and durability, making them the best type for outdoor or moisture-prone applications.
Hardboard is used in a wide variety of building applications. It can be used to construct flooring substrates, roof sheathing or wall paneling. It is also a popular material for siding or cladding, which is used to cover a building's exterior walls. Many different types of furniture and cabinets are made from a hardboard base, which can be painted or covered with wood veneer sheets to create an attractive finish.
While hardboard is often more expensive than plywood or particleboard, it also offers many advantages over these products. It has a very smooth, even surface that is free of marks, texture or wood grain. This smooth surface provides an excellent base for painting or staining, particularly in finished products like furniture or siding. It is also known for its density and strength and its resistance to cracking or splitting.
This material also has several potential drawbacks that should be considered prior to installation. Like most wood products, hardboard is highly susceptible to moisture. Exposure to rain or humidity can cause the boards to swell or warp, which can distort their appearance and lower their structural stability. While tempered grades are more moisture-resistant, they should not be considered waterproof, and should only be installed in conjunction with appropriate moisture barriers.
Hardboard can be difficult to sand properly, in part because of its fiber-based construction. The edges of the board are also susceptible to chipping or breaking, and must be handled carefully to minimize damage. Finally, buyers should be aware that tempered hardboard can be difficult to paint. The linseed oil that is added to increase moisture-resistance also tends to keep paint from adhering to the surface.