What is MDF?
Medium-density fibreboard (MDF) is a man-made, wood-based, sheet material which has a huge range of applications in construction, furniture-making and interior design.
|It is made by combining wood fibres with wax and a resin binder, or glue. MDF is heavier than plywood, but not as strong.|
A brief history of MDF
|MDF as we know it today was first developed in the US in the 1960s, but a similar product, hardboard (compressed fibreboard), was accidentally invented by William Mason in 1925. He was trying to find a use for the huge quantities of wood chips that were being discarded by lumber mills.|
|Mason was attempting to compress wood fibre into insulation board but forgot to shut down his equipment and ended up with a durable thin sheet instead. It was what you might call a happy accident!|
What is MDF used for?
|Although originally developed for making furniture, MDF has a very wide range of applications, including doors and mouldings, skirting boards, internal panelling and shelving. Much modern furniture has just a thin layer of real wood - a veneer - glued to the visible sides and edges, with MDF as the main component underneath.|
|Although MDF is mainly used indoors, moisture-resistant exterior grades are available for some outdoor applications.|
MDF has a relatively hard, flat, smooth surface. It is more uniform that natural woods as it has no knots, rings or other blemishes. However, it is generally not as strong as plywood, tending to sag more easily under weight.
Guard against splitting
Like natural wood, it may split when screws are driven in without pilot holes, but it’s an excellent material for cutting and shaping by hand or machine.
Smooth-shank nails and fine-pitch screws don’t hold well in MDF and screw retention in the edge of the material is poor - MDF tends to split most often when drilling and screwing in its edge, especially when using a tapered wood screw, which acts like a wedge to drive the fibres of the MDF apart.
Special screws, with a coarse thread, are available for use with MDF.
MDF is heavier than its chief rivals, plywood and chipboard.
Most MDF contains a substance called urea formaldehyde, which may be released from the material through cutting and sanding. Urea formaldehyde can cause irritation to the eyes and lungs.
Keep out of water
Unsealed MDF is easily damaged by water, which can cause it to expand quite quickly.
How dense is it?
MDF has a typical density of 600-800 kg per cubic metre, in contrast to particle board (160-450 kg per cubic metre) and high density fibreboard (600-1450 kg per cubic metre). For applications where weight is a prime consideration, lower-density board is used - which usually means particle board, also known as chipboard, or plywood.
How is MDF made?
Softwood logs that have been stripped of their bark are passed through a chipper machine that chops the wood into small pieces.
Sawdust and recycled chips may also be added. Some manufacturers add other materials, including expired telephone directories, old newspapers and recycled cardboard cups.
The material is then fed into a defribrating machine, which breaks down the wood into its most basic and smallest parts, known as pulp. The pulp is passed to a conveyor belt and sprayed with wax and resin glue. The wax makes the material more water-resistant and the resin binds it together.
The pulp is formed into a thick mat in a machine called a pendistor, exiting at a consistent thickness onto another conveyor.
After being rough-cut, the panels are fed into a press where a high temperature and extreme pressure compress the panels to the final desired thickness.
After cooling, the MDF panels are cut to final finish sizes and both faces are passed through a large sanding machine to complete the process.
The most common binder for boards intended for dry environments is urea-formaldehyde. Other binders may be used depending on the grade of board and its intended end-use. .
For example, melamine urea-formaldehyde, phenolic resins and polymeric diphenylmethane diisocyanate (PMDI) are generally used in boards that require an improved moisture resistance.
What are the different types of MDF?
The most common, and cheapest, is standard interior grade material, suitable for most internal applications where moisture is not a consideration.
Moisture and fire resistant
Other types of MDF include moisture-resistant and fire-retardant grades.
Exterior grade MDF can be used externally for cladding or signage work.
There’s also melamine- and acrylic-faced MDF – pre-finished board available in plain colours, woodgrains, stone and metal effects for use in kitchens, bathrooms, furniture and shop-fitting.
What sizes are available?
MDF comes in large sheets, typically 4ft X 8ft (1220mm X 2440mm), although some can be as long as 10ft (3050mm).
It’s available in a range of thicknesses, from ⅛ inch (3mm) through to 1¼ inches (about 30mm). MDF at any thickness is easy to machine and provides an ideal painting surface.
What standards are there for MDF?
British and European standards
The current British Standard for MDF manufacture is BS EN 622-5:2009, titled "Fibreboards - Specifications - Requirements for dry process boards (MDF)".
There are also European standards for MDF and the adhesives used to make them - manufacturers who prove that they comply with these standards can use the CE mark on their products.
You might also want to check that the wood content of any MDF you buy comes from sustainable sources.
What alternatives are there to MDF?
High density fibreboard (HDF), particle board and plywood are the main alternatives to MDF.
HDF contains more wood fibre per cubic metre than MDF, making it denser, and so heavier. It is used where extra hardness is needed, for instance as the core material for laminate flooring.
Particle board, also known as chipboard, is made in a similar way to MDF but the wood component is in the form of small particles rather than fibres. At similar thicknesses, particle board is not nearly as strong as MDF, although it serves well for the construction of kitchen carcases and worktops when covered with moisture-proof vinyl.
Standard MDF and particle board are prone to swelling across their thickness when they get wet, so should not be used in applications where there is a risk of water contact unless they are melamine or vinyl coated, or the MDF is the moisture-resistant type.
Even then, edges need to be perfectly sealed.
Plywood is the strongest of the four types of board, due its construction - it is made up of several layers or "plies" of real wood glued together, with the grain of each ply at an angle, usually 90 degrees, to adjacent plies, giving it stregnth in all directions. It is better for construction work where strength is needed, but is more expensive than the other boards.
Of course, real wood is another alternative, but is considerably more expensive than manufactured boards and usually doesn't come in handy sheets - lengths of real wood have to be joined together edge to edge to make a panel.
What type of manufactured board is most in demand?
Figures from the UK's Forestry Stewardship Council (FSC) show that MDF is the most demanded fibreboard at 29%, with chipboard (particle board) a close second (26%), followed by plywood (20%) and high-density fibreboard (HDF) at 17%.
Advantages and disadvantages of MDF