Appearance Grading

 

Appearance grading is the process of sorting timber into groups based entirely on the appearance of the surface of the timber. Some timber used in buildings will make use of this type of timber. This may include:

 

• Flooring and panelling
• Items for stairs: handrails, balusters, balustrades, stringers, and treads.
• Joinery and architectural trim: picture rails, architraves, skirting boards, shelves, door and window frames and hardware, fireplaces.
• Cabinets: built in cupboards, benches, furniture

 

To grade according to appearance, the timber is carefully examined by a trained grader for the presence of growth characteristics such as large or loose knots, for production degrade effects such as splits or cracks, and for cup, bow, spring and warp or twist. The timber can be sorted as to the severity of any of these characteristics in each board. In general, the most severe of any of the appearance characteristics in the appearance grades will govern the grading of the timber.

 

Note – A structural grading method introduced in Structural grading known as ‘visual stress grading’. This is a different process, in which trained graders identify structural characteristics by looking at the timber.

 

Appearance grade products are usually used whenever timber is

 

• Touched
• Closely viewed
• Part of the character of the structure or building
• Turned, carved etc.

 

Appearance grades

 

Appearance grading standards

AS2796 Timber – Hardwood – Sawn and milled products

AS4785 Timber – Softwood – Sawn and milled products

 

Appearance grading rules have been written for a number of specific timber products – eg timber floorboards. The rules focus on things that can be seen easily in the boards as they pass quickly by the graders on the grading table. Grading rules include the presence of:

 

• Knot size and frequency. It doesn’t matter where the knots are in the cross section, it is the size and number of knots per unit area in the board that is important. Knots  can be classified as:
  • Loose knots and holes, are knots where the old branch is loose in the board and has either fallen out (hole) or can be moved (loose knot). Loose knots will often eventually fall out as the timber dries a little more or is dropped or handled. Loose knots and holes lead to safety concerns for floorboards and handrails, and may affect the utility of other appearance products. They are rarely permitted.

   

  • Unsound knots are knots with the bark on the branch captured in the wood of the board. The knot may not be loose at the time of grading, but may become loose later in its life.

   

  • Sound knots, tight knots, intergrown knots are all different ways of describing knots that are well bonded to the parent wood of the board. They do not present problems for the use of an appearance product, but they will affect the classification of the piece. 

 

• Splits, cracks, checks . A crack is any gap in the surface of the piece. A split is a crack that extends from one side of the piece to the other. They are most likely at the ends of a board. A check is a crack that does not extend through the depth of the board. They are commonly caused during seasoning, and can often be filled with the surface treatment. Splits are rarely permitted in appearance grades, and checks may be permitted with size limits on the length and frequency of the checks.

 

• Colour, grain uniformity. The colour of the timber is very important in appearance products. Colour matching may be required, and while colour is hard to define absolutely, some appearance grades may have requirements for colour of the product to be uniform or have limited variation. Likewise, because many appearance products are touched, the surface texture can be important. Appearance grade descriptions may include limits on surface irregularities.

 

• Utility  For some products there may be limits on the extent of geometric irregularities that may limit the practicality of using the timber in an appearance role:
  • wane, is the extent of some missing wood (which once was the very outside of the tree). One corner of the piece was very close to the bark, and in places where the tree was bent or had an indentation, the corner of the piece was actually outside the wood in the tree. In some cases, wane can contribute interest to a piece of appearance grade timber. But in other cases, wane on the front face, will break up the uniformity of the decorative timber.
  • want is also the extent of some missing wood, but this time it has been knocked out of the piece during manufacture. Forks on forklifts or other mechanical handling has gouged a piece of wood out. Want on a back face of an appearance product will not cause a serious problem even though on the front it may be quite unacceptable.
  • cup is turning up of the edges in a board. Small amounts of cupping may go unnoticed, but significant cupping may make an appearance product quite unsuitable for its role.
  • bow is lifting of the ends in a board and in thin products, it does not present a serious problem. Generally fixing can remove the effects of bow.
  • spring is curvature of the board about its major axis (in the plane of the board) and is the most serious of the utility problems. In wide sections, even a small amount of spring can make an appearance product unusable.
  • twist  is lifting of a corner of a board, and it can present utility problems similar to bow. Provided the product is thin, it can generally be taken out by normal fixings.

 

While some industry standard appearance grades are in use for the supply of special appearance products (such as furniture blanks), where specific features or appearance are required, designers can write their own appearance specification. For particularly important applications, architects may personally select the timber for their work from local timber stocks or even directly from the mill. (This was the case for much of the timber used in the internal finishes of Australia’s Parliament House).

      

 

AS2796 Timber – Hardwood – Sawn and milled products

 

This standard has a lot of parts –

 

Part 1 Product specification – this standard is used for the specification and production of:

• strip flooring
• overlay flooring
• light decking
• parquetry flooring
• lining boards
• dressed boards
• joinery
• mouldings
• cladding, fascia and bargeboards

 

Each product has its own specification which includes any relevant utility requirements

 

Part 2 Grade description

This part gives definitions of the five softwood appearance grades. Including summary table.

 

Part 3 Timber for furniture components

This part has similar grade description as in Part 2, but with some tighter utility requirements as well – eg cup, bow, spring, twist.

 

 

AS4785 Timber – Softwood – Sawn and milled products

This standard has a lot of parts –

Part 1 Product specification – this standard is used for the specification and production of:

• strip flooring
• light decking
• lining boards
• dressed boards
• joinery
• mouldings
• cladding, fascia and bargeboards

Each product has its own specification which includes any relevant utility requirements

 

Part 2 Grade description

This part gives definitions of the five softwood appearance grades. Including summary table.

 

Part 3 Timber for furniture components

This part has similar grade description as in Part 2, but with some tighter utility requirements as well – eg cup, bow, spring, twist.

 

 

Appearance grades

 

Material is classified into different appearance grades depending upon the presence or absence of various features  on the surface of the timber. Designers specify the appearance grade they want depending upon whether they wish to have only clear timber, or timber with varying amounts of features or characteristics. Features include knots, gum veins etc. There are different grades and grade rules for hardwoods and softwoods, because each have different types of features.

 

Hardwoods:

• Select – almost clear wood, uniform colour in each piece
• Medium feature – some visual features, but limited in size and frequency, may contain variations in colour within a piece
• High feature – many features present, including some features that may affect the surface smoothness of the piece, no requirements on colour uniformity.

 

  Feature grade messmate

 

  Select grade mountain gum panelling

 

  Medium feature grade Blackbutt

 

 High feature grade Sydney Blue Gum

 

  Select Tasmanian Oak

 

 High feature grade jarrah

 

  Select grade jarrah

 

 

 

 

 

SUMMARY OF PERMISSIBLE FEATURES IN HARDWOOD PRODUCTS

 

Feature	SELECT GRADE (SEL)	MEDIUM FEATURE GRADE— Standard (MF)	HIGH FEATURE GRADE (HF)
On exposed surfaces
Tight Knots and any associated voids; individually or in aggregate in any 1 m of board length	Not exceeding 15 mm or 1/4 of the surface on which it occurs	Not exceeding 40 mm or 1/3 of the surface on which it occurs	Not exceeding 50 mm or 3/8 of the surface on which it occurs
Loose Knots	Not permitted	Not permitted	As for holes
Holes (borer, non-enclosed termite galleries and other)	Not exceeding— 2 mm (largest dimension)   6 in any 100 mm x 100 mm or equivalent area   12 in any 300 mm x 300 mm or equivalent area	Not exceeding— 3 mm (largest dimension)    20 in any 100 mm x 100 mm or equivalent area   30 in any 300 mm x 300 mm or equivalent area	Pinhole unlimited Other than pinhole, largest dimension— Not exceeding 3 mm 20 in any 100 mm ´ 100 mm or equivalent area 30 in any 300 mm x 300 mm or equivalent area Exceeding 3 mm and not exceeding 10 mm 3 per 1m of board length   Exceeding 10 mm not Permitted
Slope of grain	Not exceeding 1 in 8	Not exceeding 1 in 8	Not exceeding 1 in 8
Tight gum veins	Not exceeding— surface width measured across the feature, 2 mm individual length, 250 mm aggregate length, 1/2 the length of the piece	Quartersawn; surface width measured across the feature, not exceeding 5 mm Backsawn— Extent across face unlimited. Surface width measured across the feature not exceeding 60 mm Individual length not exceeding 1 m Depth not exceeding 2 mm	Quartersawn; surface width measured across feature, not exceeding 5 mm Backsawn— Extent across face unlimited Depth not exceeding 2 mm
Loose gum veins	Not permitted	Not one surface to another Not intersecting an end Surface width measured across the feature, not exceeding 3 mm   Agg. Length not exceeding 1/5 of the length of the piece	Not one surface to another Not intersecting an end Surface width measured across the feature, not exceeding 3 mm   Agg. Length not exceeding 1/5 of the length of the piece
Gum pockets, latex pockets and overgrowth of injury	Not permitted	Not one surface to another   Surface width measured across the feature, not exceeding10 mm   Length not exceeding 50 mm   Depth not exceeding 2 mm when backsawn	Not one surface to another   Surface width measured across the feature, not exceeding 15 mm   Length not exceeding 75 mm   Depth not exceeding 2 mm when backsawn
Knot checks	Not permitted	Width not exceeding 2 mm	Width not exceeding 3 mm
Checks other than internal (Note 1)	Width not exceeding 1 mm   Individual length not exceeding 250 mm	Width not exceeding 2 mm   Individual length not exceeding 250 mm	Width not exceeding 2 mm
Stain (Note 2) Natural discolouration Other discolouration including sticker marks	Slight (Note 3)	Unlimited	Unlimited
	Not permitted	Not permitted	Not permitted
Black speck	Slight	Unlimited	Unlimited
Non-Lyctid-susceptible sapwood (which includes appropriately treated sapwood)	Unlimited	Unlimited	Unlimited
Burls	Unlimited	Unlimited	Unlimited
Hobnails	Unlimited	Unlimited	Unlimited
Want, wane and mechanical damage	Not permitted	Not permitted	Not permitted
On concealed surfaces
Features listed above if not specified below	To the limits on the exposed surface of HIGH FEATURE GRADE	To the limits on the exposed surface of HIGH FEATURE GRADE	To the limits on the exposed surface of HIGH FEATURE GRADE
Want, wane and mechanical damage	Not exceeding— 1/3 of the width of the surface on which it occurs Agg. Length 300 mm	Not exceeding— 1/3 of the width of the surface on which it occurs   Agg. length 300 mm	Not exceeding— 1/3 of the width of the surface on which it occurs Agg. Length 300 mm
Stain	Unlimited	Unlimited	Unlimited

 

 

Softwoods:

• Clear – no features, clear wood only, very uniform appearance, no checks
• Appearance – few features, some small checks allowed
• Select – some small, clean features, essentially uniform appearance
• Standard – obvious features, mottled appearance
• Utility – few restrictions on features, may contain surface irregularities

 

  Select grade backsawn radiata pine

 

  Utility grade radiata pine

 

  Select grade backsawn radiata pine

 

  Select grade Cypress pine             

 

 

SUMMARY OF PERMITTED FEATURES IN PINUS PRODUCTS

Feature	Clear grade	Appearance grade	Select grade	Standard grade	Utility grade
On exposed surfaces
Sound tight knots:   Any partial encasement not exceeding 1/2 of the perimeter of the knot                       Any partial encasement exceeding 1/2 of the perimeter of the knot	Not permitted                               Not permitted	Individually or in aggregate in any 1 m length of board—not exceeding 1/5 of the width of the surface on which it occurs   Partial encasement—not permitted                   Not permitted	Not exceeding ½ of the surface on which it occurs             Any associated void—not exceeding 3 mm and not extending from one surface to another     Width not exceeding 10 mm—no more than 3 in a piece   Width exceeding 10 mm but not exceeding 20 mm— no more than 1 in a piece	Not exceeding 2/3 of the surface on which it occurs             Any associated void—not exceeding 6 mm and not extending from one surface to another     Width not exceeding 10 mm—unlimited     Width exceeding 10 mm but not exceeding 20 mm— no more than 2 in a piece	Not exceeding 3/4 of the surface on which it occurs             Any associated void—not exceeding 20 mm and not extending from one surface to another     Width not exceeding 30 mm—unlimited     Width exceeding 30 mm but not exceeding 3/4 of the surface on which it occurs—no more than 2 in a piece
Loose knots and all holes (including knot holes, cone holes and borer holes)	Not permitted	Not permitted	Width not exceeding 10 mm—no more than 3 in a piece	Width not exceeding 12  mm—no more than 4 in a piece	Width not exceeding 12 mm—unlimited   Width exceeding 12 mm but not exceeding 30 mm— no more than 3 in a piece
Slope of grain	Decking—not exceeding 1 in 8   Other—not exceeding 1 in 5	Decking—not exceeding 1 in 8   Other—not exceeding 1 in 5	Decking—not exceeding 1 in 8   Other—not exceeding 1 in 5	Decking—not exceeding 1 in 8   Other—not exceeding 1 in 5	Decking—not exceeding 1 in 8   Other—not exceeding 1 in 5
Pith	Not permitted	Not permitted	Width—not exceeding 10 mm     Length—not exceeding 300 mm	Width—not exceeding 10 mm— unlimited   Width exceeding 10 mm but not exceeding 15 mm,  length—not exceeding 300 mm	Width—not exceeding 10 mm— unlimited   Width exceeding 10 mm but not exceeding 15 mm, length—not exceeding 300 mm
For light decking only	Material within 100 mm of the pith—not permitted	Material within 100 mm of the pith—not permitted	Material within 100 mm of the pith—not permitted	Material within 100 mm of the pith—not permitted	Material within 100 mm of the pith—not permitted
Resin pockets, bark pockets	Not permitted	Not permitted	Width—not exceeding 6 mm   Length—not exceeding 50 mm   Extending from one surface to another— not permitted	Width—not exceeding 10 mm   Length—not exceeding 75 mm   Extending from one surface to another— not permitted	Width—unlimited     Length—unlimited   Extending from one surface to another— not permitted
Knot checks	Not permitted	Width—not exceeding 1 mm	Width—not exceeding 1 mm	Width—not exceeding 2 mm	Width—not exceeding 2 mm
Checks other than internal	Not permitted	Width—not exceeding 1 mm	Width—not exceeding 1 mm	Width—not exceeding 1 mm	Unlimited
Needle trace	Permitted, provided no decay and surface is unbroken	Permitted, provided no decay and surface is unbroken	Permitted, provided no decay	Permitted, provided no decay	Unlimited
Stain	Not permitted	Not permitted	Slight	Slight	Unlimited
Want, wane and mechanical damage	Not permitted	Not permitted	Not permitted	Not permitted	Not permitted
On concealed surfaces
Features listed above if not specified below	To the limits on the exposed surface of this grade	To the limits on the exposed surface of this grade	To the limits on the exposed surface of this grade	To the limits on the exposed surface of this grade	To the limits on the exposed surface of this grade
Knot checks	As for exposed Surface	As for exposed surface	As for exposed surface	Unlimited	Unlimited
Want, wane and mechanical damage	As for exposed surface	As for exposed surface	Width—not exceeding 6 mm on the face or edge on which it occurs   Aggregate length— not exceeding 450 mm   Occurrence—on one arris only	Width—not exceeding 6 mm on the face or edge on which it occurs   Aggregate length— not exceeding 450 mm   Occurrence—on one arris only	Width—not exceeding 6 mm on the face or edge on which it occurs   Aggregate length— not exceeding 600 mm   Occurrence—on one arris only
Sticker marks	Unlimited	Unlimited	Unlimited	Unlimited	Unlimited
Needle trace	As for exposed surface	As for exposed surface	As for exposed surface	Unlimited	As for exposed surface
Stain	As for exposed surface	As for exposed surface	As for exposed surface	Unlimited	As for exposed surface

 

Designers specify the grade of timber they want to use for a particular application.  For example, …

 

        

 

 

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