Kiln Dried v Air Dried Wood - What's the difference and does it matter?

We recommend that you read this page before you buy any live edge boards from us or elsewhere. If the wood is not at the right moisture content for your project then big problems can arise. A few minutes of your time now will save you hours of time, hassle and money. 

Wood Science

We mill our live edge boards and beams at different thicknesses using a chainsaw. Straight off the log, freshly-milled wood, often referred to as 'green wood', is flat, heavy and full of water. The water is contained in the wood pores as free water or trapped in the wood cells as bound water.

Wood is hygroscopic, meaning that it absorbs or releases moisture relative to the air temperature and humidity in it's environment. The board tries to reach equilibrium with the humidity in your garden or room which varies with the seasons:
  • Warm, summer air holds more moisture than cold winter air
  • It does this by constantly moving across its width and depth, either shrinking when its very dry or swelling when its warm and wet.
  • The board may twist, cup, bow and split as it dries unevenly or is forced to dry too quickly. 
  • Stopping the wood from moving creates tension in the wood fibres leading to movement defects.
  • Wood can cope with small fluctuations in humidity levels but needs to be dry enough to begin with.

The moisture content % is an important measure of how wet or dry the wood is and is measured using a hand-held meter. For example a moisture content reading of 50% means that 50% of the weight of the piece of wood is water - a good example of why you should not buy firewood by weight as half of your 'wood' is going to evaporate! 

​The moisture content of your board must be suited to its intended location and your method of building the table of furniture should allow for seasonal wood movement. If you are unsure of what this entails then please contact us and we'll be happy to advise.

Kiln Dried Wood

KILN drying uses a temperature and humidity-controlled environment to gradually reduce the moisture content over a much shorter time scale. The wood is stacked inside the kiln which is like a large insulated oven. The wood firstly undergoes a steaming cycle which opens up the internal pores of the wood releasing the trapped moisture. The cycle length varies with the wood species and thickness.
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A dehumidifying cycle then uses fans to circulate heated air through the wood, drawing out the moisture which is then extracted. The time taken may be between 2-8 weeks depending on the thickness and species of the wood. At the end of the process the moisture content will have reduced to 8-10% and the wood is now KILN dried, stable and ready for making indoor furniture . The dried wood is wrapped in plastic to prevent it gaining moisture from the air before it is used. 

Please note: It is very important that you keep your kiln dried wood indoors, It can be left in its wrapper or removed from it and kept lying flat until you use it. If you unwrap it and leave it in your workshop or garage then IT WILL gain moisture from its environment and may not stay flat for long.

Advantages:
  • Kiln dried wood is stable, easier to plane and sand smooth for finishing.
  • It can be easily joined to other sections of your furniture.
  • It stops mould and fungal growth
  • It kills micro organisms and any insects or eggs that may have lived in the wood.
  • ​If you are planning to make an epoxy river table then the wood MUST be kiln dried otherwise the epoxy may become cloudy or not set or bond properly.

Kiln dried wood does cost more than air dried wood but compared to the time invested in your project,  it's a small price to pay for peace of mind and a better result from your endeavours! 
Kiln Drying Boards
Live edge boards are stacked with battens to promote good air flow​
  • Wood is steamed at 70-75C for about a week and left to cool
  • The dehumidifying cycle operates at a different temperatures and durations depending on the type and thickness of the wood.
  • Wood is removed once it has reached 10% moisture level or less. 

Air Dried Wood

AIR drying relies on our climate using the sun and wind to evaporate some of the trapped moisture from the wood when it is stacked outside. In our temperate climate, the moisture level can fall to 20% and sometimes a bit lower in a good year. At 20% moisture the wood can be called seasoned,

This is a cost-free process but takes a long time, around one year per inch of board thickness is often quoted but longer for dense woods like oak. However at 15% to 20% moisture, the wood is not stable and further shrinking will occur if furniture made from it is placed in a heated room. The wood may develop cracks or warp creating an uneven surface. These defects may be reduced if your method of construction allows for this movement.

Advantages:
  • Air dried wood is fine to use for outdoor furniture where it's internal moisture is balanced with the natural humidity outside and can better cope with seasonal variations. 
  • It can still develop small splits and cracks however during longer periods of hot, dry weather (rare on the Isle of Man admittedly!)
  • Readily available in a wider range of lengths, widths and type of wood.
  • Cheaper than kiln-dried wood.

Air Drying Boards

  • Milled boards are stacked with regularly placed battens or stickers to promote good airflow and steady drying.
  • A waterproof cover is placed on top of the stacks with the sides left open.
  • The board surface will feel dry but the core of the board will still be quite damp. 
  • Once the wood has reached 20% moisture it can be called seasoned.