FAQ | Understanding Timber and its Natural Characteristics

Being an entirely natural product no two pieces of timber are the same. It has a number of inherent growth characteristics such as grain patterns, varying colours, knots and other defects or imperfections. The words ‘defect’ and ‘imperfection’ may sound alarming, but in the context of a natural and variable material such as timber it can mean anything already growing naturally in the tree, for example knots; or it can mean things introduced as part of the production and handling process (sawmilling, drying, machining etc.) such as wane or splits. The industry does not consider these defects or imperfections but features which only further enhance the natural beauty and individuality of a timber product.

Depending on the grade selected some or all of these defects may be permissible to a greater or lesser extent within the official industry grading rules. Generally these defects or imperfections will not adversely affect the final appearance or performance of the finished construction project especially if the installer is aware of their existence and how they can be overcome, if indeed they need to be.

By understanding timber and its unique characteristics the following information will hopefully offer an insight as to why these characteristics occur and how they can be accommodated during the installation process.


What is sticker shadow?
What is wane?
What are knots?
What is tannin staining?
What is grain / grain patterns?
What are the manufacturing marks on my pack of timber?
What is warp/warping?
What is a cup?
What is a crook?
What is a bow?
What is twisting?
What is weathering?
Is it important to sand timber?


What is sticker shadow?

Both sawn and profiled boards (e.g.decking or cladding) are stacked with sticks (known as stickers) in between some or all of the layers to allow air to flow throughout the pack during the drying process and to stabilise the packs.

With some products slight evidence of the stickers will be left on the face and back of the board. This is known in the industry as a ‘sticker shadow’ or ‘sticker stain’ and is actually a result of the oxidation of naturally occurring chemicals within the wood.

Sticker shadow is an unavoidable natural occurrence and therefore not considered to be a defect. It can be easily removed by lightly sanding, which is a required process regardless of the presence of sticker marks if you are applying a finish, because sanding provides a ‘key’ to the surface that enables the finish to penetrate into the wood. Sanding will also remove any other blemishes present on the face of the wood and will provide a cleaner surface upon which to apply the finish. If you choose to leave your wood unfinished (not recommended) the sticker marks will disappear naturally as the wood ‘weathers’.

For more information, read our Useful Guidelines to Buying Timber [PDF]

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What are knots?

Knots are the bases or portions of branches (or dormant buds) that grew on the living tree before it was felled to produce timber. All trees have branches therefore knots will be present in the timber produced from any tree.

Timber is divided up into different quality standards called ‘grades’. Knots and other natural imperfections are allowed to a greater or lesser extent in all grades. It is therefore important that the timber buyer understands that there will be a limited presence of knots within all grades, even ‘clears’. The higher and more expensive the grade, the fewer natural characteristics such as knots will be present.

Due to the fact that wood is an entirely natural material with no two pieces the same, it is impossible to accurately quantify the exact number, size and frequency of knots. The official grading rules that appear on our website describe the maximum number of knots and other characteristics allowed within each grade.

Grading Rules: Clear Western Red Cedar Cladding
Grading Rules: Siberian Larch Cladding
Grading Rules: Western Red Cedar Cedardeck Decking

What will each grade look like? How many knots would you expect? View our unpacking videos here...

In all cases our products far exceed the minimum grading standards. To gain a better understanding of the characteristics of each grade we encourage you to watch the videos and read the full product descriptions along with accompanying documents on our website. Better still, come along to our warehouse and inspect the material for yourself.

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What is wane?

Wane is missing wood or untrimmed bark along the edge or corner of a piece of timber or wood which is a result of the curvature of the log from which it was cut. Wane on a finished piece is caused when the surfacing machine or planer fails to remove all of the material from a low spot on the timber.

In some grades wane is an allowable natural characteristic and is not considered a defect. Cedardeck is one example where a limited amount of wane may be present on the reverse of the boards. As it usually only occurs on one side of the board and typically will not affect the integrity of the timber, the board can normally be turned over to reveal the good face.

If wane were to be eliminated entirely from certain grades the effect would be more wastage for the producer and therefore a significant increase in the price. As wane has no negative effect either visually or structurally on many finished projects, its inclusion is permitted within the grading rules and is factored into the price of the material.

The relevant grading rules will describe to what extent (if any) wane is allowed within each particular grade.

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What is tannin staining?

Many species of wood contain natural occurring tannins which can migrate to the surface of the wood leaving brown staining. They are drawn out of the wood by moisture which carries the staining substances from within the wood. When the moisture evaporates it can leaves patches of discolouration on the surface. Tannin stain usually occurs on new wood.

Steps can be taken to alleviate tannin stain - use properly kiln dried wood and apply a suitable finish to both sides, edges and ends prior to installation. Kiln drying reduces the moisture content of wood and makes it more stable. Applying a finish will then minimise the amount of moisture that the wood will absorb (note that the best performing finishes do not completely seal the wood, rather they allow it to ‘breathe’ - or absorb and release a small amount of moisture).

Tannin stain can be removed by washing the stained areas with a mixture of methylated spirits and water or oxalic acid.

Note that when applying an opaque finish, tannin stain may become evident on the surface of light or mid colours such as white and light grey. If this occurs wash the surface as described above, rinse thoroughly and apply another coat of finish.

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What is grain / grain patterns?

The grain is one of wood's most attractive features. Wood grain can be defined as the texture, direction and pattern of the wood fibers.

Each wood species has its own grain type, and each tree will have its own grain pattern. The direction of wood grain will vary within each tree and the way a log is cut will also affect the appearance of the grain on different pieces of wood. This means no two pieces of wood will ever be the same, in fact two pieces of wood from the same species can look very different. Despite this the overall appearance once installed will be one of homogeneity. It is this effect of subtly different grain patterns and colour tones that help give structures built from wood a beautiful natural appearance that will stand apart from those built with man-made materials.

Grading Rules: Clear Western Red Cedar Cladding

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Why does my timber have evidence of manufacturing / handling?

Timber products are manufactured and handled using industrial machinery. You should expect that with any shipment there will be occasional evidence of the manufacturing and handling process. Minor strap marks, roller marks and the odd dent or nick may be evident. When manufacturing large quantities of boards that can be up to 20’ (6.05m) in length it would simply not be possible to eliminate these marks without generating a large amount of wastage, slowing down the manufacturing process and introducing a lot of additional packaging. Clearly if this were to happen, there would be a dramatic increase to the price of the finished product, not to mention the negative impact on the environment caused by the wastage and extra packaging.

A realistic balance has to be achieved - the manufacturer must ensure that they produce a high quality product, implement strict quality control processes and package materials properly to ensure that any packing and handling marks that may occur are kept to an absolute minimum.

Conversely the timber buyer must understand that it would not be economically viable for the manufacturer to eliminate every board that may display minor evidence of the manufacturing / handing process without them charging considerably more for the product.

It is for these reasons that an understanding exists between manufacturers / suppliers and users of timber products that it is inevitable that there will be occasional minor markings on the boards caused during the manufacturing and handling process and this is factored into the price of the product from the outset.

For those with no knowledge of the timber industry and no previous timber buying experience this can be a difficult concept to grasp. Consumers are used to buying mass produced man-made products that are identical in every way. If a product of this type should have a manufacturing fault it would in most cases be obvious to all concerned and it would be replaced by the supplier or returned to the manufacturer.

With a natural material such as timber, this is less obvious. What some consumers would consider a defect can in fact be an allowable characteristic for that particular product / grade. It’s inclusion has already been factored into the price and should therefore be expected by the user.

Whilst this may sound alarming the reality is that many marks will be very minor and will only appear occasionally. In virtually all cases they will easily be eliminated during the installation process.

It should also be noted that it is often only up close that these characteristics are visible - once installed the eye is seldom drawn to individual characteristics but rather one sees the installed material as a ‘whole’.

Whilst we realise that this may sound off-putting, we feel that customers benefit from having this information as it helps them to gain thorough understanding of the product that they are buying. This would of course apply to products purchased from any supplier of timber products, not just Silva. It’s just that (to the best of our knowledge) no other timber supplier has gone to this length to provide this depth of information to their customers.

The reality is that we invest a huge amount of effort into ensuring that our products are of the highest industry standards. This starts at the buying process where we go to great lengths to source the very best raw materials. Where applicable they are properly kiln dried at source before they are shipped to us, either already as finished products or for further processing by us into finished products. Care is taken during the picking and packing process – we have a strict quality control process that eliminates unusable boards ensuring that everything that leaves our premises is on grade.

In all cases our products far exceed the minimum grading standards. To gain a better understanding of the characteristics of each grade we encourage you to watch the videos and read the full product descriptions along with accompanying documents on our website. Better still, come along to our warehouse and inspect the material for yourself.

What will a pack of timber look like? View our unpacking videos here...

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What is warp/warping?

Warp is a word used to describe any deviation from a true surface. It includes a few different issues related to movement of the wood including bow, crook, twist and cup. Warp is unavoidable and provisions are made for its allowance within the official grading rules. According to the NLGA grading rules, warp is classified as very light, light, medium and heavy. It should be noted that in virtually all cases there are quick and simple methods to eliminate warp upon installation.

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What is a cup?

The most common form of warp is cup. A board is said to cup when one face shrinks more in width than the opposite face. The rough rule of thumb is that a board will cup toward the bark side (though not in every case). An easy way to visualise this is to imagine that the growth rings are trying to straighten.

Cup is a deviation from a straight line drawn across the piece from edge to edge. It is measured at the point of greatest distance from the straight line. The wider the board the greater amount of cup is permitted. As an example, according to the NLGA grading rules if light cup is permitted then the maximum amount of cup allowed within that grade for a 6” (152.4mm) wide board is 1/16” (1.6mm). This rises to ¼” (6.4mm) for a 12” (304.8mm) board.

An example of when cupping can happen is when wood is left uncovered in the sun prior to it being installed; therefore it is important to keep wood covered when stored on site prior to installation.

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What is a crook?

Crook is a deviation edgewise from a straight line drawn from end to end of a piece. It is measured at a point the greatest distance from the straight line.

The rule of thumb with crook is that the narrower the board the greater the amount of crook is permitted and the longer the board the greater amount of crook is permitted. As an example, according to the Standard Crook Table (paragraph 810c. in NLGA Grading Rules) light crook of 2 ¼” (57.2mm) is permitted on a 2” (50.8mm) wide board of 20’ (6.05m) in length, whereas only 1/16” (1.6mm) is permitted for a 12” (304.8mm) wide board of 6’ (1.83m) in length.

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What is a bow?

Bow is a deviation flatwise from a straight line drawn from end to end of a piece. It is measured at the point of greatest distance from the straight line.

The rule of thumb with bow is that the thinner the board the greater the amount of bow is permitted and the longer the board the greater amount of bow is permitted. As an example, according to the NLGA Grading Rules light bow of 6 ¾” (171.5mm) is permitted on a board under 2” (50.8mm) thick and 20’ (6.05m) in length, whereas if the board is 3” (76.2mm) thick and over and 6’ (1.83m) in length only ¼” (6.4mm) of bow is permitted.

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What is twisting?

Twist is a deviation flatwise, or a combination of flatwise and edgewise, in the form of a curl or spiral, and the amount is the distance an edge of a piece at one end is raised above a flat surface against which both edges at the opposite end are resting snugly.

The rule of thumb with twist is that the wider the board the greater the amount of twist is permitted and the longer the board the greater amount of twist is permitted. As an example, according to the Standard Twist Table (Paragraph 810d. NLGA Grading Rules) light twist of only 3/16” (4.8mm) is permitted on a board 2” (50.8mm) wide and 6’ (1.83m) in length, whereas 3 3/4” (95.3mm) is permitted for a 12” (304.8mm) wide board of 20’’ (6.05m) in length.

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What is weathering?

All wood is susceptible to weathering once exposed to UV rays from the sun or moisture from rainfall or the general climate.

'The weathered look' is really down to personal taste. Some customers like the driftwood-like appearance, however others prefer to keep their timber looking like new with a pigmented-finish.

There is a risk involved however when leaving wood exposed to the elements. During the weathering process wood can appear unsightly as the material can blacken due to moisture getting into the fibres and pulling out tannins and extractives. This can lead to patchy, inconsistent areas of discolouration which are unpleasant to the eye. While this can naturally weather to the silver-grey look over time, the process can take years until you're left with a consistent finish. It's this stage of the weathering process which has lead some town planners to reject the use of unfinished timber cladding, unaware that it is an easily avoidable and treatable issue. Read our full article about weathering...

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Is it important to sand wood / timber?

We always recommend finishing timber in order to maintain a long lasting and consistent appearance. The secret to a perfect finish is to sand the surface prior to finishing. The more care taken with preparation, the more finish will penetrate the wood, providing an even, consistent and long-lasting finish. Studies have proven sanding can extend the life of a finish by up to 3 times compared to an unsanded surface.

What does sanding do? Read our full article about the importance of sanding...

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