Most problems with imported hardwood come back to one thing: moisture. Boards that are too wet shrink, twist and crack after machining; boards dried badly can be stressed inside and move unexpectedly; and even well-dried timber can pick up moisture in a hot, humid container. Buying kiln dried hardwood that arrives at the right moisture content, without hidden drying defects, is one of the most important skills for any importer, joiner or furniture maker.
In this guide we explain what kiln drying does, the moisture targets for different uses and markets, the drying defects to watch for, how to check kiln-dried lumber on arrival, how to avoid container condensation, and what kiln drying adds to the price. At Global Timber Trade Hub we supply kiln-dried African hardwoods dried at partner mills in Cameroon, Gabon and the Republic of Congo.
In short
- Kiln drying brings timber to a controlled moisture content suited to its use.
- Typical targets are 8–12% for interiors and 12–16% for exterior joinery.
- Ask for moisture content, tolerance and how it is measured in your contract.
- Watch for case hardening, internal checks and uneven drying.
- Check moisture on arrival and protect stock from damp.
- Kiln drying adds cost, but it saves far more in waste and callbacks.
What kiln drying does
Freshly sawn tropical hardwood can contain more water than wood by weight. If it is used wet, it shrinks as it dries in service, causing gaps, cracks, warping and loose joints. Air drying in the open reduces moisture slowly, but in tropical climates it rarely gets timber below about 15–20%. Kiln drying uses controlled heat, humidity and airflow to bring timber down to a target moisture content in weeks rather than months, and to a lower level than air drying can reach. A good kiln schedule also relieves internal stresses at the end of drying, so boards stay stable when machined.
Target moisture content by use
| Use | Typical target |
|---|---|
| Furniture and interior joinery in heated buildings | 8–10% |
| Flooring for heated homes | 8–10% |
| Interior joinery in humid climates | 10–12% |
| Exterior windows and doors | 12–16% |
| Decking and cladding | 12–18% |
| Guitars and instruments | 6–8% |
The right target depends on where the wood will end up. Timber should be dried close to the average moisture it will reach in service, so it moves as little as possible. A furniture factory in northern Europe needs drier stock than one in a humid coastal city in Asia.
Moisture targets by market
Buyers in heated, dry indoor climates such as northern Europe, Canada and the northern United States usually order 8–10% for interiors. Buyers in the Middle East may also want dry stock because of air conditioning. Buyers in tropical and humid markets often prefer 12–14%, because very dry wood would absorb moisture and swell after delivery. Tell us your market and use, and we will suggest the target.
Drying defects to watch for
- Case hardening: the outside dries and sets before the inside, leaving internal stress. Boards may cup or bow when resawn.
- Internal checks (honeycombing): cracks inside the board, often from drying too fast.
- Surface and end checks: cracks on faces or ends.
- Collapse: distorted, wavy surfaces in some species dried too hot when wet.
- Uneven moisture: some boards wetter than others in the same bundle.
- Stain: discoloration from slow drying or poor airflow.
A good mill avoids these with proper schedules for each species and thickness, and with conditioning at the end of the cycle. Dense species such as azobe, okan and moabi need slower schedules than light species such as ayous or frake.
How to specify kiln-dried hardwood
- State the target moisture content and tolerance, for example 10% plus or minus 2%.
- Say how it will be measured: calibrated pin meter with species correction, or oven-dry samples.
- Ask for stress relief or conditioning at the end of drying.
- Specify the share of boards that must be within tolerance, such as 90%.
- Ask for a kiln record or moisture report with the shipment.
Checking moisture on arrival
Use a calibrated moisture meter set for the correct species. Take readings from several boards in each bundle, at the centre of the board and away from the ends, and on both faces. For thick boards, use insulated pins long enough to reach the core, or cut a sample and oven-dry it. Record your readings with photos. A simple stress test, cutting a short section and resawing it down the middle, shows case hardening if the two halves curve inwards.
Container condensation
Timber travels from Central Africa through tropical waters to cooler ports. Temperature changes can cause condensation inside containers, known as container rain, which wets the top layers of timber and can lead to mould or stain. To reduce the risk:
- load only properly dried timber in clean, dry containers;
- use moisture absorbers hung inside the container;
- cover the top of the load with breathable sheets or cardboard;
- unload promptly on arrival and store under cover.
What kiln drying adds to the price
Kiln drying costs energy, kiln time and labour, and some boards are lost to defects. As a rough guide, kiln-dried sawn timber usually costs noticeably more per cubic metre than air-dried or fresh-sawn timber of the same species and grade, with dense species costing more to dry than light ones. For furniture, flooring, joinery and instruments, the extra cost is small compared with the waste, rework and complaints caused by wet timber. See our African hardwood prices guide.
When kiln drying is not needed
For large outdoor sections such as bridge beams, marine piles, sleepers and crane mats, kiln drying is often impractical and unnecessary. These are usually supplied fresh sawn or air dried and dry slowly in service. Engineers allow for this in design. See kiln dried vs air dried lumber.
A worked example for a furniture importer
Consider a furniture company in northern Europe that imports sapele and iroko for dining tables and sideboards. Its first container arrived at around 14% moisture content, although the order said “kiln dried”. After machining, table tops cupped in the heated showroom and joints opened on several pieces, causing returns. For the next order, the company specified 9% plus or minus 2%, measured with a calibrated pin meter at the centre of boards, with at least 90% of readings in range, and asked for conditioning at the end of the kiln cycle and a moisture report with the shipping documents. It also asked for moisture absorbers in the container and arranged to unload into its heated warehouse the same day. On arrival, the company checked a sample of boards in each bundle and ran a simple resaw test for case hardening. The timber was in range, the furniture stayed flat and returns dropped. The order cost a little more per cubic metre, but the savings in rework and returns were far larger.
Acclimatising timber in your workshop
Even perfectly dried timber needs time to settle into your conditions. Stack it flat with stickers in the workshop where it will be machined, and leave it for one to two weeks before cutting critical parts, longer for thick stock. If your workshop is much drier or more humid than the timber’s target, the boards will gain or lose a little moisture, and it is better that this happens before machining than after. For flooring, acclimatise boards in the room where they will be laid, with the heating or air conditioning running at normal levels.
Dense vs light species
Drying behaviour varies a lot by species. Light woods such as ayous, frake and ilomba dry quickly and easily but can stain if not dried promptly. Medium woods such as sapele, sipo and iroko dry fairly well with proper schedules. Dense woods such as azobe, okan, tali, moabi and mukulungu dry slowly and need gentle schedules to avoid checks and case hardening, which is why kiln-dried stock in these species costs more and takes longer. Allow for this in your lead times.
Lead times and payment
Kiln drying adds time to an order: from about two to three weeks for thin light species to six weeks or more for thick dense stock. Plan orders accordingly. For first orders, a letter of credit or a deposit with balance against copy documents protects both sides. See our letter of credit for timber guide.
Kiln-dried stock by species
We supply kiln-dried boards in most of our species, from light ayous and frake to medium sapele and sipo and dense moabi and okan. Tell us the species and use, and we will confirm the moisture range we can deliver and the time needed. See also our sipo wood price guide.
For mixed containers, we dry each species to its own schedule and target, then pack and label bundles separately so you can check each one on arrival.
Common mistakes
- Ordering “KD” without a number: always state the target moisture.
- Measuring only the ends: ends dry faster than the core.
- Storing KD stock outside: it reabsorbs moisture.
- Machining immediately: let timber acclimatise first.
Our honest advice
Write the moisture target, tolerance and measurement method into every contract, check timber on arrival, and store it properly. Kiln-dried hardwood dried well and kept dry will save you more than its extra cost many times over.
Sources
Related guides
- Timber inspection before shipment
- Sapele lumber
- Hardwood lumber grades
- Wholesale hardwood lumber
- Shop all species
Frequently asked questions about kiln dried hardwood
What moisture content should kiln dried hardwood have?
About 8–12% for interiors and 12–16% for exterior joinery, depending on climate.
How do I check kiln dried timber?
Use a calibrated meter with species correction, reading the centre of several boards.
What is case hardening?
Internal stress from uneven drying that makes boards cup or bow when resawn.
Does kiln dried timber need storing indoors?
Yes. It reabsorbs moisture if left in rain or damp conditions.
Get a kiln dried hardwood quote
Send us your species, moisture target, sizes, volume and destination through our quote form. We will reply with a firm price and lead time.