Timber Fundamentals

Most buyers who get burned on a timber order were not cheated. They bought a specification they could not read. The species was right, the price looked fair, and the material arrived too wet, too heavy, too hard to machine, or perfectly sound for a job it was never going to survive.

This page is for the reader who is commercially competent but not yet technically confident — someone who can read a quotation but cannot yet tell whether the thing being quoted makes sense. The aim is not to hand you a table of facts to memorise. It is to give you the four or five properties that actually decide whether a timber suits a use, and enough of the reasoning behind each that you can interrogate a specification you have never seen before.

Two deliberate omissions. You will not find per-species figures on this page — densities, hardness values, durability classes, shrinkage percentages. Those live in the timber species directory, where each entry carries what we have actually assessed for that species, and a gap is shown as a gap. Nor will you find grading rules or class boundaries; grading is its own discipline and has its own hub at the Quality & Grading Academy.

Wood is not a manufactured material

Every property below varies. It varies between species, between two trees of the same species, between the butt log and the crown, and between two boards cut from the same log an hour apart. It also keeps varying after the timber is sawn, because wood responds to the air around it for as long as it exists.

That single fact is what separates timber from steel or plastic. A specification that would be redundant for a manufactured product — stating a moisture content, a tolerance, a grade, an acceptable range rather than a number — is doing real work here. When a supplier gives you a single figure for a property that genuinely varies, they are either quoting a typical value or they have measured this lot. Which one it is matters, and it is a fair question to ask.

Heartwood and sapwood are two different materials

A growing tree carries living, conducting wood in an outer band and inert wood at the centre. As the tree ages, the inner wood stops conducting sap and is infiltrated with extractives — the compounds that give many tropical hardwoods their colour, their smell and, crucially, their resistance to fungi and insects. That inner wood is heartwood; the outer band is sapwood.

The consequence is blunt: when a species is described as durable, that describes its heartwood. Sapwood is generally lighter in colour, less durable and more attractive to insects and staining fungi in almost every species, including the very durable ones. So a specification for an exterior application that does not say how much sapwood is acceptable has left the most important question open. "Heartwood only" is a real, quotable requirement, and it costs more, because it means more of the log is waste.

Sapwood also takes preservative treatment far more readily than heartwood, which is why treated timber and naturally durable timber are not interchangeable answers to the same problem.

Moisture content is the property to get right first

If you take one thing from this page, take this one.

Wood is hygroscopic: it exchanges water with the surrounding air until it reaches an equilibrium with the temperature and humidity around it. Moisture content is the weight of water in a piece expressed as a percentage of its oven-dry weight, and it is not a fixed property of a species — it is a property of this piece, on this day, in this climate.

Freshly felled tropical hardwood is very wet. Drying it does three things at once:

• It shrinks. Wood loses no dimension at all while it is giving up the free water sitting in its cell cavities. Only once that is gone and the cell walls themselves begin to dry does the piece start to shrink — and from that point, shrinkage is roughly proportional to further moisture loss. This is why half-dried timber keeps moving.
• It becomes stronger, stiffer and lighter, and generally easier to machine, glue and finish. Coatings and adhesives applied to wet timber fail.
• It becomes far less hospitable to decay fungi and staining organisms, which need moisture to work. This is why a sealed container of insufficiently dried timber arrives mouldy.

Shrinkage is also uneven. Wood moves considerably more across the grain than along it, and more in one across-grain direction than the other — which is why a drying board cups, bows or twists rather than simply getting smaller, and why the way a board was cut from the log changes how it behaves. Movement along the length of a piece is small enough to ignore for most purposes.

The number that matters is the one for the environment the timber will live in, not the one for the yard it was sawn in. Timber dried to suit a humid tropical climate and then installed in a heated interior in a cold-winter market will keep drying after it is installed — and shrink, open joints and cup after you have paid for it. Timber dried too far for its destination will take up moisture and swell. Neither is a defect in the wood. Both are specification failures.

Which is why moisture content is the line most often missing from an enquiry and the one most often regretted. It is effectively unfixable after arrival: re-drying a container of boards is not a commercial option, and the damage drying-in-service does — cupping, splitting, joints opening — has already happened by the time you see it.

Air dried, kiln dried, and what each actually promises

Air drying means stacking the timber with spacers so air moves between the boards, and waiting. It is cheap, gentle and slow, and it is limited by the climate: air drying cannot take timber below the equilibrium the local air supports, which in a humid tropical environment is well above what a heated interior in a temperate market demands.

Kiln drying uses a controlled chamber to reach a specified target that air drying cannot reach, faster and more consistently, and with the capacity to relieve the internal stresses that drying sets up.

The practical points a buyer needs:

• "Kiln dried" is not a moisture content. It is a process. Ask for the target and the tolerance, and ask whether it is an average across the parcel or a maximum for any piece — an average conceals wet boards.
• Ask how it was measured, and ask for the readings, not a summary. Moisture meters read the surface region; a thick board can be dry outside and wet in the middle, which is exactly the piece that moves later.
• Drying is reversible. A kiln-dried parcel that then sits uncovered in a humid yard, or travels in a container that sweats, is no longer at the moisture content on the certificate. Protection after drying is part of the specification, and the Export Academy covers what a five-week sea voyage does to a poorly protected load.
• Thick sections and dense species dry slowly, and rushing either produces surface checking, internal splitting and case-hardened boards that distort the moment they are re-sawn. If a lead time for heavy kiln-dried stock sounds impossibly short, it may be.

How drying is actually done in Cameroon, and what a mill can and cannot offer, is covered in the Processing Academy.

Density predicts most of what you will care about

Density — mass per unit volume, conventionally quoted at a stated moisture content, because it changes with moisture — is the single most useful summary property of a timber. It is a reasonable predictor of hardness, strength, stiffness, abrasion resistance and, unhelpfully, of how difficult and expensive the material is to work.

Its consequences run through the whole transaction:

• Weight. Timber is traded by volume in CBM, but it is shipped by weight, and dense tropical hardwood reaches a container's payload limit long before it fills the box. A denser species means fewer cubic metres per container and a different freight cost per cubic metre. Two quotes for the same CBM of two different species are not comparable shipments.
• Machining and fixing. Dense timber blunts tooling faster, needs slower feeds and sharper cutters, and frequently has to be pre-bored before nailing or screwing. That is labour and consumables in your workshop, not the supplier's.
• Handling and fastening on site, and the structure that has to carry it.
• Drying behaviour. Dense species generally dry more slowly and are less forgiving of being rushed.

The spread across Cameroon's export species is wide enough that "tropical hardwood" tells you nothing useful on its own — a lightweight joinery timber and a heavy engineering timber are both accurately described by the phrase and are not remotely the same product to buy, ship or machine. The species directory records the density range we hold for each species; read it as a range, because it is one.

"Hardwood" does not mean hard

This is the most common technical misunderstanding in the trade, and it costs people money.

Hardwood and softwood are botanical categories, not descriptions of hardness. Hardwoods are broadleaved trees; softwoods are conifers. The categories describe what kind of tree the wood came from and how its cells are arranged — nothing more. There are hardwoods softer and lighter than common construction softwoods, and the same is true in reverse.

Cameroon's export catalogue is overwhelmingly tropical broadleaved hardwood, so inside this trade the word does almost no discriminating work at all. If you want to know whether a timber is hard, ask about density and, where you care about surface wear and denting, hardness measured as such — the directory records a Janka figure where we hold one. If you want to know whether it will last outdoors, ask about durability. "Hardwood" answers neither question.

The related trap is the commercial vocabulary. Groupings like primary hardwood, secondary hardwood, promoted species and specialty wood — which this site uses to organise the catalogue — describe market position: how much of it is traded, how established it is, what price band it sits in. They are not quality judgements and not technical classifications. A promoted lesser-known species can be technically excellent for your job and materially cheaper precisely because fewer buyers ask for it by name.

Durability is a claim about a context

"Naturally durable" means the heartwood resists fungal decay without preservative treatment. It is measured against decay in ground contact, and it is expressed in classes. Two things about those classes matter more than their numbers.

First, durability is not a property, it is a property-in-a-situation. The same board in three places behaves in three ways. Buried in damp soil, it faces the hardest test there is. Exposed above ground where it wets and dries, it faces a real but lesser one. Kept permanently dry indoors, it faces essentially none — and in that setting a "not durable" species will outlast the building, which is why the least durable timbers in the catalogue are entirely correct choices for interior joinery, furniture and plywood. Asking "is this durable?" without naming the exposure produces an answer that cannot be wrong and cannot be used.

Second, natural durability classes describe resistance to decay fungi, and not much else. Insect attack — and in particular marine borers, if the timber is going into or near seawater — is a separate question with separate answers. So is weathering: an untreated durable timber left outdoors will still grey, check on the surface and move with the seasons. It is not rotting. It is also not going to look the way it did on the day it was fitted, and a client who was not told that will call it a defect.

Two further cautions worth carrying:

• Durability classes apply to heartwood only. See above. Sapwood in a durable species is not durable.
• Variation within a species is substantial — by tree, by growing conditions, by position in the log. Class assignments are a central tendency, not a guarantee for the piece in your hand.

Grain, texture and figure

These three words get used interchangeably and mean different things.

Grain is the direction and arrangement of the wood fibres. Straight grain machines predictably. Interlocked grain — where the fibre direction reverses from one growth increment to the next, which is common in tropical hardwoods — is strong and resists splitting, but it tears out on planing unless the tooling is sharp and the cut is taken the right way. Your machinist will notice long before your purchasing department does.

Texture is the scale of the cell structure: fine and even, or coarse and open. It determines how the surface takes a finish and how much filling an open surface needs before it can be polished.

Figure is the visible pattern on a cut surface — the effect of grain, colour and the cutting angle together. The ribbon or stripe figure that makes some quartersawn tropical hardwoods desirable is a product of interlocked grain seen on a particular face. Figure is an appearance property. It is priced as one, it varies within a lot, and if it is what you are actually buying, then the sample you accepted and the way the boards were cut both belong in the contract.

How a board is cut from the log affects all of this at once — appearance, stability, movement — which is one reason boules, sawn through-and-through and kept in sequence, exist as a traded form. The Products Academy covers the traded forms; the Processing Academy covers conversion.

Colour changes, and that is normal

Freshly sawn tropical hardwood is not the colour it will be. Many species darken substantially with light and air over weeks to months; some lighten. Timber matched perfectly at the mill can differ visibly by the time it is installed, and a repair made a year later in the same species from the same supplier will not match the surrounding work until it has caught up.

This is a common and entirely avoidable dispute. If colour matters, agree it against a sample, agree it in the state it will actually be seen in, and say so in writing. The Buyer Academy covers how to get that into a specification that suppliers can quote against.

Reading a specification: the questions worth asking

Given all of the above, a specification you can trust answers these, and an enquiry that asks them gets back quotes you can compare:

1. Which species, botanically? Trade names overlap and travel badly. Fix the botanical name.
2. Heartwood only, or is sapwood acceptable — and how much?
3. What moisture content, to what tolerance, measured how — and is that the right figure for the destination environment?
4. Air dried or kiln dried, and if kiln dried, to what target?
5. What is the exposure? Interior, exterior above ground, ground contact, marine. Durability is meaningless without this.
6. What grade, under which grading rule? See the Quality & Grading Academy.
7. What dimensions and tolerance, and is width and length fixed or random?
8. Is appearance — colour, figure, matching — part of what you are buying? If so, against what sample?

The three mistakes that cost the most

Specifying a species and stopping there. A species name is roughly a quarter of a specification. Without moisture content, sapwood allowance, grade and dimensions, two suppliers quoting the same species are quoting different products, and the cheaper one is telling you something true about which product it is.

Treating durability as absolute. "It's a durable species" is not a suitability assessment. A durable heartwood in ground contact, in the tropics, with sapwood left on, is a different proposition from the same species in a sheltered interior — and the sales sentence covers both.

Ignoring movement in service. Wood keeps exchanging moisture with its surroundings for its whole life. Design for it, detail for it, and condition the timber to its destination before it is fixed in place. Most "quality problems" reported months after delivery are movement problems that were designed in.

Where to go next

Work from the material outwards. The species directory holds the properties we have assessed for each Cameroonian species — density range, durability class, hardness where known, characteristics and typical uses — and shows the gaps honestly. Cameroon Timber 101 covers the origin itself; the Products Academy covers the traded forms — sawn timber, logs, boules, veneer — and the Processing Academy covers what happens between forest and container.

When you know what the material needs to be, the Buyer Academy covers turning that into an order and the Export Academy covers getting it to you. You can browse the marketplace to see what is actually being offered, check the supplier directory for who handles it, or post an RFQ and have several suppliers quote one written brief. Unfamiliar terms are defined in the Cameroon timber glossary.

About this hub

Timber Fundamentals currently holds no articles. This pillar page is all there is of the hub so far, and rather than pad it out with confident detail we would be guessing at, it stays deliberately general where the underlying property is genuinely variable — which, in wood, is nearly everywhere. You will not find per-species densities, hardness values, durability classes or shrinkage figures written into this prose; those belong to the species directory, which records what we have actually assessed and leaves a gap visible as a gap. Where we have not assessed something, the page says so.