Medium density fibreboard - MDF

[edit] Introduction

Medium-density fibreboard (usually referred to as MDF) is an engineered, timber-based sheet material which has a hardness and density that is comparable to solid timber. It is one of the most versatile building materials available as it is homogeneous, relatively inexpensive and durable and so can be used in many woodworking and carpentry applications as a low-cost alternative to timber.

MDF is very much a material of the modern age, having entered into large, commercial-scale production as late as the 1980s. Made from compressed wood fibre and binder, MDF can be faced on both sides with a very fine, smooth painted or veneered finish. When cut, MDF reveals a very fine-grained, uniform structure that is more dense than plywood.

[edit] Physical properties

The finished board usually comprises at least 80% wood fibre, the remaining constituents being the urea-formaldehyde resin glue, water and paraffin wax. MDF is much denser and stronger than particle boards such as chipboard and hardboard, and is also denser than plywood. However, despite its robust surface, standard MDF has poor resistance to moisture and the lower grades may swell when saturated. Moisture resistant versions are now available, as is low density fibreboard and high density fibreboard.

[edit] Manufacture

In essence, MDF can be conceived of as sawdust and glue. It is manufactured from residual matter derived from hardwoods or softwoods broken down into very fine fibres which are then combined with wax and resin binder. Improved moisture resistance can be imparted by using alternative binders such as melamine urea formaldehyde.

Manufacturers can add a host of materials into the timber mix, including various woods, forest thinnings, straw, bamboo, recycled paper, carbon fibres, polymers, scrap and waste from saw-mills and so on. The mixture is then pressed into sheets under high pressure and temperature and allowed to cool.

The production of composite board products generally uses one of two processes a dry process and a wet/dry process. The forner uses synthetic binders often formaldehyde-based agents or glues to binding the wood fibers under pressure. The latter might use steam and pressure along with increased levels of natural binders to glue or cement the wood fibres together to form a board. There are also a number of variations inbetween the two processes and the environmental impacts of the two types of process can be significant, so it is worthwhile asking about manufactiring details. MDF production is also starting to use more environment-friendly (non-toxic binders).

[edit] Working and machining

Due to its density, MDF is a heavy material: a full sheet of 18mm-thickness MDF can weigh around 45kg. Once it is cut, the edges machine well and can be painted or lipped with a strip that matches the wear surfaces. The use of a router will usually leave a crisp profile with no splintering, burning or tear-out. It is also an ideal substrate for veneers.

MDF can be glued, laminated and dowelled, however cutting and sanding – both best undertaken outside rather than inside – result in a very pervasive, invasive dust which necessitates the use of a respirator and possibly other precautions. Furthermore, free formaldehyde which can be hazardous to health may also be released during working.

Although the facing of MDF is harder than most woods, the core tends to be softer therefore dropping a panel onto one of its corners or even the edges can result in deformation. This means handling MDF can demand more care in handling than timber or plywood.

[edit] Supply

MDF can be supplied in its raw state, or with smooth-sanded surfaces or decorative facings. It is available in a range of sizes – typically 2,440 x 1,220mm, in thicknesses from 6mm to 25mm or more. It is typically supplied as general purpose, moisture resistant or fire retardant.

[edit] Related articles on Designing Buildings Wiki

• Adhesives.
• Blockboard.
• Cedar.
• Chipboard.
• Confederation of Timber Industries.
• Cross-laminated timber.
• Engineered bamboo.
• Glulam.
• Laminated veneer lumber LVL.
• Lime wood.
• Modified wood.
• Oriented strand board.
• Plywood.
• Softwood.
• Timber.
• Timber construction for London.
• Timber preservation.
• Timber vs wood.
• Types of timber.