The characteristics of standard grade MDF in the middle thickness ranges have been sufficient for most furniture and interior design applications up to now. Any relatively new material is however subject to continuing development. As a consequence of developments in the last 2 to 3 years, MDF manufacturers are now able to offer a wider range of standard boards covering thicknesses down to 1.8mm and up to 60mm, and speciality boards with improved moisture resistance, low formaldehyde emission, flame retardancy, and higher density. These enhancements of standard grade MDF have been achieved by changes in manufacturing procedures, different resin binders or the use of additives. An increasing volume of these speciality boards are now being used in the furniture, interior design and building industries and for outdoor applications.
A. Thin MDF
Several MDF manufacturers are now offering thin boards starting at 1.8 mm thickness. These can be considered as alternatives to hardboard and thin plywood with the added advantage of being smooth on both surfaces and free the grain features which can show through paint finishes and thin foils applied to plywood substrates. Now that the properties of very thin MDF boards are well defined in the 1.8 to 2.5mm, greater than 2.5 to 4mm and greater than 4 to 6mm thickness bands of the European Standard EN 622-5, designers and specifiers have all the information necessary to make good use of these materials in furniture, interior fitments and buildings.
Typical applications in furniture include drawer bottoms, backs of cabinets and centre panels in framed doors. All the finishing and surfacing treatments applied successfully to thicker MDF can equally be applied to thin MDF.
In building interiors, thin MDF can be used for wall and ceiling panelling, as skins for flush doors, partitioning, office screens, lightweight doors and exhibition panelling. Experience has shown that thin MDF can easily be cut using steel rule dies or blanking presses. Hole patterns punched through the board provide an opportunity for a wide range of decorative panels some with acoustic properties. Another possibility, worthy of further exploration is the manufacture of curved panels, reception desks, bar fronts and shop counters for instance, constructed by laminating several layers of thin MDF in a former to build up the required shape and thickness.
B. Thick MDF
Several manufacturers are now able to supply MDF up to 60 mm thickness compared with an upper limit of approximately 30 mm several years ago. Previously, users requiring thick MDF had to laminate several thinner boards to achieve the required thickness. The properties of these thicker boards are specified in the greater than 30 to 45mm and the greater than 45mm thickness bands of EN 622-5.
The greatest potential for these thicker boards is in buildings as architectural features, columns, pilasters and archways, for instance, where the good surface and edge finishing characteristics of MDF can be used to good advantage. Other possibilities include heavy duty flooring and shelving, worktops, stair treads, bench seating and internal doors with deep moulded faces.
Taking advantage of the good machining characteristics of MDF, slabs cut from thick boards can be turned to form a wide range of table legs, underframes and display or exhibition features. Thick MDF is also widely used as a base material for wood veneer and foil wrapped mouldings.
C. Low formaldehyde MDF (Class E1)
The formaldehyde content of standard grade MDF can vary according to the nature of the urea formaldehyde or other resin used as a binding agent. MDF will normally be supplied with a free formaldehyde content, measured by the EN 120 (perforator) method, not exceeding 30mg/100g. (Class E2, EN 622-1). MDF which satisfies this requirement is considered to be suitable for most applications in furniture, interior design or buildings where sufficient ventilation is available to remove small quantities of formaldehyde as they are emitted.
MDF with a low formaldehyde content (Class E1, EN 622-1) of not more than 9 mg/100 g is available as standard board from some manufacturers, other manufacturers produce low formaldehyde boards according to customer needs.
Low formaldehyde MDF, is recommended for all applications where the ventilation is likely to be restricted, where damp conditions or high ambient temperatures prevail or where the occupants of a building have special needs, in sheltered accommodation, schools and hospitals, for instance. Low formaldehyde MDF should be used for showcases and other fitments for museums to minimise possible corrosion of metal artifacts by formaldehyde products.
Note should be taken of any national regulations which may refer to the use of low formaldehyde boards for building components and furniture. Users should also take note of the effect of any surface coatings on formaldehyde emission. Some, such as acid catalysed lacquer and paper foil, may increase formaldehyde emission while others such as plastics laminate, PVC foil, polyurethane lacquer and cured melamine paper can reduce the emission from the surfaces of MDF panels.
D. Moisture resistant MDF (MDF.H and MDF.HLS)
MDF with improved resistance to moisture for interior applications involving exposure to relative humidities up to 80%, with only short term exposure to higher relative humidities, is manufactured by upgrading the normally used urea formaldehyde resin binder or by using an alternative moisture resistant resin. All the desirable properties of standard grade MDF are retained in these boards with the added advantage of a higher level of strength retention and less swelling when used in extreme interior conditions or sheltered outside conditions.
The likely performance of moisture resistant MDF in extreme conditions is checked on a quality control basis by exposing test specimens to a demanding cyclic conditioning test repeated three times, each cycle comprising immersion in cold water, freezing in air and drying in an oven at 70°C. Swelling in thickness and tensile strength perpendicular to the plane of the board (internal bond), are measured after completing the full conditioning treatment.
EN 622-5 refers to two grades of moisture resistant board, MDF.H, for general use in humid conditions and MDF.HLS for load bearing use in humid conditions.
Possible applications for moisture resistant MDF include the following:
- Bathroom furniture
- Kitchen furniture
- Window boards
- Double glazing infils
- Skirting boards
- Stair components
- Architectural mouldings
- Informative signs in semi exposed situations
Where intermittent contact with water is likely in kitchens and bathrooms, for instance, and some building applications, special care should be taken with the sealing/finishing treatments, particularly in respect of exposed edges.
E. Exterior MDF (MDF.E)
As part of the further development of MDF, an exterior grade is now available with all the good machining and finishing characteristics and substantially higher strength than standard MDF, with the added advantage of resistance to outside exposure conditions, subject to adequate sealing of all surfaces and edges with a proven exterior durability coating.
As an indication of durability, road signs manufactured from exterior grade MDF and subjected to the extremes of weather have been used for eight years without signs of deterioration. It has also been used successfully for shop fronts exposed to the elements for several years.
The likely performance of exterior grade MDF is assessed as part of the manufacturers quality control procedures by subjecting test pieces to one or more accelerated ageing tests giving results which have been correlated with the results of field trials.
As exterior grade MDF is a relatively new development, users should obtain relevant performance specifications and guidance on application suitability and, particularly on finishing treatments, from the board manufacturers or their agents.
Possible applications for exterior grade MDF in non structural situations include:
- Road signs
- Advertising hoardings and business signs
- Shop fronts and facia panels
- Garden furniture Playground fittings
- Boat cabin linings
- Exterior mouldings
- Sports score boards
- Shelving in open storage areas
- Exterior door panels
F. Flame Retardant MDF
Standard grade MDF would normally be expected to achieve the same surface spread of flame ratings as other wood based sheet materials and wood itself when assessed by the appropriate national standard of each country. An improved surface spread of flame rating can sometimes be achieved by coating the surfaces of standard grade MDF with an intumescent paint or other specially formulated finish, subject to achieving the specified coating weight.
Alternatively, the surface spread of flame characteristics of standard grade MDF can be uprated by impregnating manufactured boards or panels with fire retarding salts using a vacuum pressure impregnation process. As water based solutions are normally used for this impregnation treatment, some raising of the surface fibres and loss of strength is inevitable.
The most satisfactory method of achieving a high resistance to surface spread of flame for MDF requires the addition of the appropriate flame retarding salts to the fibres as an integral part of the board manufacturing process. Boards of this type are now more generally available and should be used in preference to boards which have been treated after manufacture. A wider range of finishing materials can be used on these impregnated boards without significant loss of flame retardancy.
Possible applications of flame retardant MDF include:
- Wall and ceiling linings
- Office partition systems
- Institutional furniture
- Builtin fitments
- Exhibition displays
- Bulkhead and cabin linings in ships
Methods of test for flame retardancy and the regulations referring to the need for fire rated materials in buildings vary between countries. The industry has developed a range of products with different levels of flame retardancy to satisfy these different requirements, including some with an enhanced level of flame retardency to satisfy demanding requirements. In the absence of a European norm, users should refer to National standards or codes of practice when selecting a particular type of flame retardant MDF and the associated finishing treatment.
G. High Density MDF (also referred to as HDF)
Standard grade MDF in the thickness range 12 to 19 mm normally has a density in the range 700 to 800 kg/m3. Higher density grades of MDF are now available with densities in excess of 800 kg/m3. This increase in density is achieved by increasing the amount of resin binder added to the fibres, increasing the bulk density of the fibres used to form the mat, and increasing the pressure applied to form the board, all factors together resulting in a substantial increase in strength.
The even closer compaction of the fibres in high density MDF enhances the machining characteristics of the board allowing more complicated profiles to be cut. The well compacted surfaces and edges result in excellent paint finishes with only minimum surface preparation. Several bedroom and kitchen door manufacturers are using high density MDF to take advantage of these good machining and finishing characteristics.
High density MDF can be processed in the same way as standard grade MDF. The finishing treatments applied to standard grade MDF can equally be applied to high density MDF with better results.
National or European standards for MDF do not include any reference to high density MDF. Manufacturers supplying these products will be able to supply full specifications for their own brands. As a general rule, high density MDF will have performance levels substantially higher than the levels specified for standard boards in the EMB Industry Standard.
Possible applications for high density MDF include:
- Industrial shelving
- Work benches
- Heavy duty flooring
- Furniture underframes
- Doors for kitchen and bedroom units
The board manufacturer should be consulted before using high density MDF for structural applications involving high static or repeated impact loads.
H. Decorative surfaced MDF
1. Wood veneered.
Standard grade MDF is widely used as a base for wood veneering for many applications in the furniture and interior design industries. Large furniture companies are likely to have their own wood veneering facilities. Interior design companies and small furniture companies without these facilities can obtain wide ranges of wood veneered MDF boards and panels from some MDF manufacturers or from specialist fabricators who provide a wood veneering service using veneers from a standard range or specially selected veneers to suit customers requirements.
2. Melamine surfaced.
A high durability finish can be obtained by direct surfacing MDF with melamine resin impregnated papers essentially following the high temperature, high pressure, laminating procedure used for the manufacture of melamine surfaced chipboard. A wide range of decorative effects are available, including plain colours, woodgrains, prints, all with smooth finishes or textures built into the surfaces at the time of laminating. Having regard for the sophistication of the short cycle or continuous laminating press procedures, melamine surfaced MDF cannot easily be produced by non-specialists companies. However, a wide range of melamine surfaced MDF with an even wider range of finishes is available from those board manufacturers who provide this important value added service or from specialist laminators.
3. Paper and PVC foils.
Some MDF manufacturers and many specialist laminating companies can supply MDF sheets surfaced with any one of a large number of decorative paper and PVC foils. The thickness, decorative effect and durability of the surfacing material can be selected to suit the requirements of particular applications. Subject to the selection of foils with suitable finishes, these boards can be used without the need for further finishing treatments.
MDF overlaid with plain or textured papers are available from some manufacturers for painting applications where the requirements for appearance are particularly demanding, high gloss finishes, for instance.
4. Textured surfaces.
Some MDF manufacturers are now offering standard grade boards with a texture embossed into the surface as a secondary manufacturing operation. These also can be finished effectively by direct painting.
5. Paint and Lacquer finishing
Some MDF manufacturers have increased their product range by the introduction of boards and panels with decorative surfaces achieved by painting or lacquering. Thin MDF manufacturers in particular can supply painted or wood grain printed boards for door skins and wall panelling.