the different types explained
Specifying the type, thickness and grade of material and the spacing between the supports largely depend upon the weight being supported by the shelving. The article below just gives some general guidelines for comparison between materials and advice should, where possible, also be obtained from the supplier or manufacturer of the shelf material. This article only deals with material for the shelf itself, see our other articles for supporting shelves and fixing the supports to walls.
The different types of loads supported by shelves can be considered as:
- A light load can be considered to be vases, small plants, trinkets etc.
- A medium load can be considered to be a shelf full of average sized paperback books.
- A heavy load can be considers to be large plants and hardcover books, etc.
The actual classification of the intended load should be 'common-sense', if in doubt, build stronger shelving and, before putting a heavy item on a shelf, consider what load the shelf was originally designed for.
The overhangs of a shelf at each end (beyond the supports) should always be kept to a minimum, usually the 'rule of thumb' is no more than 20% of the distance between the supports.
Timber - solid wood is fairly strong and is available in various planed sizes which will suit most shelving needs - where the width of shelf cannot be obtained in one piece, tongued and grooved timber board can be used to form one surface which will not separate through warping - an alternative is to use separate planks joined edge to edge using dowels etc.
Timber is easy to work with and can be finished in a variety of ways - e.g. paint, varnish, polishes etc.
The thickness of timber required to avoid sagging between supports depends upon the distance between the supports and the load being placed on the shelf. 18mm thick timber should be considered the minimum thickness and the supports should not be spaced more than 700mm apart - with 25mm thick timber the supports should not be spaced more than 900mm apart.
Slatted timber - when a shelf is only to support a light load, a slatted shelf can be made up using narrow pieces of timber fixed to battens - the battens are then secured to the supports. This gives a wide shelf using less timber than a solid shelf.
Usually the finished board is as strong as solid softwood timber and generally it looks as good except when viewed very close up.
It is easy to work with and can be finished in a variety of ways - e.g. paint, varnish, polishes etc - some cheaper board may have a lot of filler used to build up the surface, this filler may be detrimental when a clear finish is required.
Different thicknesses of laminated board are available, use the same support spacings as given above for solid timber.
Plywood - this is made by bonding various numbers of thin layers together, each layer having the grain running at rightangles to the adjacent layers. Plywood is stronger, and less likely to sag, than chipboard and laminated chipboard.
It is easy to work with although the finish of the cut edges will probably be fairly rough and may need a trim to hide the different exposed layers. Plywood can be finished using paint or varnish.
Use 18mm thick plywood as a minimum and have supports at no greater than 700mm apart for all but the lightest of loads.
Chipboard is made up of wood particles bonded together under heat and pressure - it is classified by its density; normal, medium and high-density.
- Normal is fairly soft and 'flaky' and not really suitable for shelving.
- High-density is very hard and solid (often used for worktops and fire doors) - usually an 'overkill' for shelving.
- Medium density is in between Normal and High density.
Plain chipboard - unlaminated chipboard is the cheapest and weakest of all the material covered here. Generally it is considered unsuitable for shelving as the finish is so poor.
Laminated chipboard - laminated chipboard comes with a number of different types of veneers covering the faces (but usually not the ends). It is cheaper than solid timber but is not so strong - it tends to sag overtime except when used to support very light loads.
Consider 12mm thick laminated chipboard as a minimum and have supports no more than 300mm apart for all but the lightest load. When using 18mm thick chipboard, the spacing for the supports can be increased to 700mm.
Blockboard is less likely to sag and is stronger than chipboard - providing that the core strips of softwood run lengthways.
Blockboard is easy to work with - the ends will probably need a trim to be fitted to cover the exposed ends of the different strips. It can be finished with paint or varnish.
Consider 18mm thick blockboard as a minimum and have supports no more than 700mm apart for all but the lightest load.
Care needs to be taken when when working with MDF - it is manufactured using urea-formaldehyde resin which can be harmful. Adequate ventilation and wearing a face mask when machining it are essential, and breathing in MDF dust must be avoided.
The urea-formaldehyde resin may also be released in low concentrations over a long period of time; not everyone is adversely affected but some people can be, just by having a piece of MDF in a room.
MDF can be finished with paint or varnish - it should always be sealed in some way, not left bare.
Consider 18mm thick MDF as a minimum and have supports no more than 500mm apart for all but the lightest load. When using 25mm thick MDF, the spacing of the supports can be reduced to 700mm apart.
Glass - Clear, coloured or obscured glass can be attractive shelving for light loads - many DIY stores stock pre-cut glass shelving either as part of a complete shelving kit or on its own - special brackets are needed for glass shelving, they incorporate lips and clips to locate the glass in place.
The glass used for shelving needs to be toughened (a process carried out after the glass has been cut to size); once toughened, the glass cannot be re-cut to a new size. If a 'non-standard' size glass shelf is required, a glazing merchant can cut the glass to size and have it toughened. Never use ordinary glazing glass.
Shelf stiffener - Any timber based shelf material can be stiffened to stop it sagging between supports and to increase the load it can carry. Just glue and screw a wooden batten to the underside of the shelf half way across its width - the length of the batten should be such that it just fits between the supports.
A batten fixed to the wall at the back of the shelf which the rear of the shelf can rest on can be used on its own or in combination with a batten under the shelf - in this event, the batten under the shelf should be moved towards the front edge.
Softwood (or hardwood) edge moulding of a width to suit the shelving thickness, can easily be cut with corner mitres, and then glued and pined to the edges to hide the cut edges of the shelving.