Ah, wood. A wonderful material full of natural goodness: solid timber worktops are durable, attractive, often innately hygienic…
However, there are other little idiosyncrasies associated with these natural properties. Wood’s unique structure means that it’s constantly expanding and contracting – and when fitting solid wood kitchen furniture, such as worktops, this fact must be taken into consideration.
Moisture means movement – or does it?
Wood has a certain amount of moisture present within its structure. Within freshly cut timber, there are two types of liquid: ‘free’ water and ‘bound’ water. ‘Free’ water denotes the liquid sap that fills the cell cavities – around 70%. The remaining 30% – the ‘bound’ water – soaks into the cell walls, causing the wood fibres to swell.
As this young or ‘green’ wood dries, the water begins to evaporate: first the free water, then the bound. Free water isn’t such an issue: when these levels change, the structure isn’t really affected. However, if bound water is lost, the wood will contract.
We can say that wood dries to a degree but not to an absolute: its position is not stable, because the amount of bound water fluctuates with atmospheric conditions. On average, for every 5 per cent change in surrounding humidity, wood loses or gains about 1 per cent of its moisture.
Note: it’s the relative humidity – not the absolute humidity, which we’ll come to – that is important when analysing moisture and movement. Relative humidity refers to the ratio of the actual moisture in the air to the maximum amount of moisture the air can hold at its current temperature.
In basic terms, the air will hold more moisture the warmer that it is. This means that the absolute humidity (amount of moisture the air can hold at its present temperature) can change while the relative humidity is unchanged – for instance, if the air temperature and the absolute humidity level rise at the same time. In this scenario, the relative humidity would remain constant, and timber present within this climate would not move.
How wood moves
The grain structure of the wood means that movement is not confined to one direction.
- Direction 1: Tangent. Wood moves quite a lot in this direction (tangent to the growth rings). When freshly cut, timber can shrink up to 8 per cent along these lines.
- Direction 2: Radial. Wood moves much less in this direction (extending from the pitch along the growth rings). When freshly cut, timber tends to shrink up to 4 per cent only along these lines.
- Wood also moves along the longitudinal line, but this is minimal.
As a result of these directional fluctuations, quartersawn timber – the type used by Worktop Express® – is more stable than the plain-sawn variation (quartersawn lumber is cut radially whereas plain-sawn is cut tangentially). For example, when quartersawn lumber dries, both faces shrink equally and the board remains flat (whereas the outside face of the plain-sawn lumber is more likely to shrink faster than the inside face, causing distortion).
That said, due to the felling process it’s often not possible to utilise just one type of sawn timber; therefore the best solid wood furniture – such as the worktops produced by Worktop Express®” – tends to use a combination of the two board types, balancing structural integrity with other important qualities (such as appearance).
It should be borne in mind that external forces can also cause movement in the wood. For example, the development of the tree itself or improper drying can cause stress within the timber; when this timber is cut, the wood will relax slightly and react by changing shape.
However if you purchase worktops from a reputable source like Worktop Express®, you can feel assured that only superb, well-treated timber will be coming your way. Our timber is prepared in state-of-the-art kiln driers, with no time limit – we wait as long as is needed for the timber to dry thoroughly, ensuring premium quality.
That said, there is nothing that can be done to prevent the natural movement of wood. As long as atmospheric conditions change, wood will contract and expand in accordance – but we can keep this to a minimum and prevent any issues with some simple installation and maintenance guidelines.
Here are some top tips:
- Ideally, solid wood worktops will be installed as soon as possible after delivery, but we appreciate this might not always be convenient. If storing your worktops, be sure to oil these first and then lay flat in an indoor room with a stable humidity.
- When installing your worktop, be sure to allow a 3-4mm gap between any walls or units adjacent to the worktop edges (paying special attention to the back of the worktop and the wall). This is known as the ‘expansion gap’ and, as the name suggests, will allow the worktop breathing room to expand and contract with changes in humidity without causing damage.
- If fitting a worktop over an appliance or exposed brickwork, be sure to affix a moisture barrier to the underside of the worktop (to protect the timber from any fluctuations in heat and moisture).
- If fitting a worktop near a freestanding heat source – such as a range cooker – allow a gap of at least 30mm all the way around the worktop. We also recommend fitting a solid wood end cap along the edge for extra protection.
- Oil your worktop regularly; while this won’t stop the timber from moving naturally, it will provide general protection and keep the wood in good condition.
The benefits of owning a superb natural material like solid wood are endless – so don’t be fazed by these natural properties, they really are easy to handle! Just a little maintenance will ensure a long, trouble-free life for your worktop.
And don’t forget that the Worktop Express® team are always here to help. For more tips, please view our installation and aftercare guide here, or contact us and we’ll be happy to answer any questions.