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First, let’s look at the nominal sizes of woods, and the types of wood available…

Sizes…
The woods you are likely to use in projects are sold in what are called nominal sizes (measured in mm [cross-section] and mm or m [length]). That’s the size it is cut to – while ‘wet’ at the mill. After cutting, it is dried (or cured) (often in the open air, or in a kiln) – which causes it to shrink a little – and only then it is ‘planed all round’ (p.a.r.) to smooth the surfaces. So the final dimensions are 3 to 6mm less depending on the timber, and the accuracy with which it is planed.

This means the dimensions can vary by a millimetre or two – so what you buy as 22x44mm, for example, is almost always exactly that – but it might differ slightly and be 21 x44mm, 23x44mm or even 22x43mm. It also happens that sometimes the dimensions can vary along a length, so always check.

Hence:

Nominal size (mm)Actual size (what you see on the label) (mm)
13 x 10212 x 96
13 x 15212 x 144
25 x 2522 x 22
25 x 5022 x 44
25 x 7622 x 69
25 x 10222 x 94
25 x 15222 x 144
25 x 22822 x 222
38 x 3832 x 32
38 x 5032 x 44
38 x 7632 x 69
38 x 10232 x 94
38 x 15032 x 144
38 x 22832 x 220
50 x 5044 x 44
50 x 7644 x 69
50 x 10244 x 94
50 x 15244 x 144
76 x 7669 x 69
76 x 10269 x 94
76  x 15269 x 144
38 x 7632 x 69
38 x 10232 x 94
38 x 15032 x 144
38 x 22832 x 220
50 x 5044 x 44
50 x 7644 x 69
50 x 10244 x 94
50 x 15244 x 144
76 x 7669 x 69
76 x 10269 x 94
76  x 15269 x 144

The lengths (m) vary from 1.2, 1.83, 2.4, 3 and 3.6m, but you can usually order special lengths if necessary or have longer lengths cut to the lengths you want – though you will get to take the offcuts home as well as the store is very unlikely to be able to sell on random lengths to other customers. Hence, if you want a length of 1.4m, for instance, a 1.83m length will be cut to that length, and you will also take home the 400mm or so offcut.

Selecting wood

Hints on selecting wood…

  • Check the exact dimensions along a length and at a couple of intervals along the length
  • Avoid wood with too many knots – they are weaknesses within the wood so when cutting wood for load-bearing members, try to avoid knots as much as you can.
  • Rest one end on of the timber on the floor and sight along it with the longest cross-section dimension held vertical and see if the wood is straight or not.
  • Sight along the length again laying the longest cross-section horizontal and check if the wood is curved.
  • Check the cross-section – is the timber bowed – when the cross section is not flat but curved?

Manufactured wood

Manufactured wood, as the name implies, is manufactured from grown woods.

Plywood

Plywood comprises veneers of wood, each about 1mm thick, glued together in sheets with the grain of each alternately at 90° to those above and below it. In the case of finishing ply, such as that with an oak finish, the top will be the oak veneer while the bottom veneer will be SA pine or similar and intended to be the (unseen) back of the panel.

There are always an odd number of veneers, and broad applications are: commercial – general use; marine – boats and boating (or where there is exposure to weather); decorative – panels in furniture and other applications where appearance is important.

Plywood is coded for specific qualities: BR – boil resistant (a boil is when a surface veneer separates from the one below in a limited area – rather like a blister); Comm – commercial; Combi – commercial interior and exterior; Decorative – in furniture; Ext – exterior use; Flexiply – very flexible for use in rounded applications; Int – interior use only; Lloyds Approved – suitable for nautical/marine applications; MR – moisture resistant; WBP – weather and boil proof resistant and hence suitable for exterior use.

Bear in mind that exterior ply can be used indoors, but interior ply should not be used for outdoor applications.

The higher the specification, the more you can expect to pay, but whatever ply you select, always seal the edges, sides and surfaces to protect it against moisture.

The full sheet size (in mm) is 2440×1220, half sheet is 1220×1220; quarter is 1220×610, and it’s generally available in thicknesses (mm) of 3, 3.6, 4, 6, 9, 12, 18, 21 and 25.

MDF (Medium Density Fibreboard)

MDF is made from wood fibres glued under heat and pressure, and because it has no grain, it can be sanded, sawn or routed in any direction. It is also dense, flat, stiff, and has no knots. Its density means that routed contours are smooth (though a little light sanding with fine grit sandpaper [220-360-grit] can improve the surface and produce a good finish). It’s often used for cupboard doors, counter tops, office furniture and other applications where a smart finish is required

It should be sealed properly on all surfaces and edges for most applications, particularly for bathroom cabinet doors and so on, to prevent moisture penetration. If moisture does penetrate the material, it will swell and start separating.

Like plywood, it’s sold in sheets (mm) of various thicknesses (mm). The 4mm sheet is 2052×732; 6mm is in two sizes, namely 2440×1220 and 2750×1830; and MDF 9, 12, 16, 18, 22 and 30mm thick is sold in sheets 2750x1830mm.

Chipboard

This is a less dense product than MDF, but made using basically the same principles. The chips, as the name implies, are larger, so routed edges, for instance, are poor. You will also find that the chip density is greater at the surfaces but less dense towards the middle of the sheet. Chipboard is normally available in 2440×1220 sheets (or subdivisions), and also in sheets 305, 450, 500, 610mm wide for shelving and cupboard sides, for example. Thicknesses range from 12 to 25mm. This product must be well sealed if it’s being used anywhere where the moisture content of the air is high as chipboard soaks up water like a sponge.

The giveaway is when the chipboard swells, often first along the edges. Chipboard is used in shelving and cheaper grades of furniture. More expensive versions have a veneer added and may also be edged – this is when veneer is glued along the edges.

Chipboard is also used in melamine countertops, 35mm thick and in widths up to 600mm or so and in lengths up to 3m. This version is often the material of choice in the kitchen and best installed by professional kitchen fitters. Make sure it is well sealed around the sink area and along the boundary between the countertop and the wall.

Masonite and tempered hardboard

Masonite and tempered hardboard are two versions of a high density manufactured board, dark brown in colour and available in similar sizes and thicknesses as is plywood. They are often used as backing for cupboards and the like. They are not waterproof and will deteriorate when exposed to water, but they are easy to work. One surface is smooth with a slight satin gloss while the reverse is textured.

Laminated board

Laminated board comprises narrow strips of softwood with widths ranging from 25mm up to about 80mm, glued edge to edge and end to end and with no two adjacent joins lining up (think of how a bricks are laid). The aim is to create joints that are abutted on both sides by solid timber – giving this type of board substantial strength. Boards are usually 15, 18, 22 or 28mm thick, in widths of 400, 450, 500 or 600mm. Because the grain is exposed and the joinery is very tight, this product often resembles natural timber.

This makes it a good choice for furniture where the natural gain can be left exposed, but if you are using it outdoors, then you need to seal the ends, edges and both surfaces completely as the glue used to bond the laminates is water-based and when moisture penetrates, it fails and the strips separate. Lengths range from 1.2m to 2.1m.

A variation on laminate board is laminated beams, this time the laminated timbers are glued top to bottom, and are 65mm wide by 200mm deep. A characteristic of this type of manufactured timber is its great strength. Again the exposed grain lends itself to varnishing so these timbers are often to be found in home structures as exposed support beams for upper floors, upper decks and patios (where they will be viewed from underneath and similar applications where load bearing and appearance are important.

These beams can also be made in various curved arcs and shapes, but this is very much the realm of the architect who might require laminated beams of particular profiles and curves for a specific design of building.

Blockboard

Blockboard is essentially laminated board with a plywood veneer added to the upper and lower surfaces as – like the above-mentioned laminated board – it comprises a core of softwood strips (up to about 25mm wide) glued as per laminated board.

The result is a product with a natural appearance, except on the sides and ends where the strips are visible. This product is usually limited to thicknesses around 30mm and is sold in sheets 2440x1220mm (or subdivisions).

Dowels

Dowels are available in diameters ranging in increments from 4mm up to 22 and more and in lengths ranging from just over 900mm, to 1.2m, 1.8m and so on.

Mouldings

In the old days most woodworkers would have to create the mouldings they wanted by using chisels or wood planes using blades with different profiles.

Nowadays, you can buy a wide range of mouldings – ranging from skirting boards to finish off the bases of walls where they meet the wall-to-wall, to mouldings that can be used for decorative effects on just about any woodwork project or surface.

What wood?

There is a wide range of woods available for indoor and outdoor use but generally, the two you are most likely to use are either SA pine – widely used in furniture, items for the home, trellises etc – or meranti. The former is a wide-grained, soft wood and your most economical choice whereas the latter is a darker, imported variety, but equally suitable for a wide range of applications.

You can order other woods such as light oak, teak and what-have-you but bear in mind that some imported timbers might have different nominal sizes from those quoted above, you might need to adapt your design accordingly. Also bear in mind that as they are imported, they can be very expensive.

At the end of the day, however, whatever wood you select, you need to ensure that it is well protected from whatever might assail it in the environment in which you will set it up or be using it. So in the next article we will look at preserving and protecting wood from the elements, insect pests and other damaging agents.

Here are examples of some woods. Mica stores generally stock SA pine and meranti, so if you need any of these woods, you will probably have to place a special order.

  1. Scots Pine
  2. Norway Spruce
  3. European Larch
  4. Common Juniper
  5. Aspen
  6. Hornbeam
  7. Silver Birch
  8. Alder
  9. Beech
  10. Pedunculate Oak
  11. Wych Elm
  12. Wild Cherry
  13. Pear
  14. Norway Maple
  15. Small-leaved Lime
  16. Ash

Panel:

Most of these materials are available at Selected Mica Stores. To find your closest Mica and whether or not they stock the items required, please go towww.mica.co.za, find your store and call them. If your local Mica does not stock exactly what you need (for instance, some of the more exotic woods) they will do their best to order it for you or suggest an alternative product or a reputable source.