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Wood and wood products can be treated in various ways to change certain properties. There are methods to affect the wood’s durability, hardness, dimensional stability and moisture absorption. These methods can be divided up into:

  • Treatment against fungal and insect attack
  • Fire protection treatment
  • Dimensional stabilisation
  • Hardening

Treatment against fungal and insect attack

Wood protection usually refers to measures that in various ways aim to protect wood and wood-based materials against attacks by wood-decaying fungi, blue stain, mould, insects and marine pests (such as shipworm).

When building in wood, the structure should be designed to prevent such attacks, giving what is known as structural protection. The goal is for the wood not to have too high a moisture content for a prolonged period of time. Temporary damp should be able to quickly dry out and the moisture content should be able to return to normal levels.

There are situations where structural wood protection cannot be achieved and high moisture content levels are a permanent feature. In such cases, wood with better durability can be used. There are types of wood and parts of the tree trunk that offer better durability than others. There are also options for modifying wood to increase its durability. In addition, chemicals can be added to the wood to give greater durability.

GRADING SYSTEMS

Currently there are basically two grading methods of sawn timber ldwide:
1. Grading of a piece on the basis of the number of “standard” defects it has in relation to its size;
2. Grading on the basis of clear surfaces, which means that the grader calculates the percentage of square surfaces clear of defects that are properly defined in relation to the whole surface of the piece. In this way a percentage of defect-free surface is to be obtained, which defines – mainly – the grade of the piece. This is the method used in, among others, the Malaysian Grading rules (MGR), the National Hardwood Lumber Association Rules (NHLA) and the SATA Rules Sciages Avivés Tropicaux Africains: Traditional African Sawn Timber. This causes a certain amount of confusion as several different qualities carry the same name. Originally the United Kingdom was the dominant trading partner; which explains the fact that the various qualities are in English. Grading has been an oral “system” for a long time, until certain producers and users tried to transform it into a written from, but it never became an encompassing and uniform rule. This grading rule is known under the name « Empire Grading ». In order to avoid all disputes and differences in interpretation of this (originally oral) grading scheme, ATIBT’s Commission III has decided to to make a synthesis of these rules.

– GENERAL REMARKS .
1. Timber will be well-sawn, with dimensions above contractual dimensions to allow for shrinkage by drying and such to satisfy the contractual dimensions at 20% moisture content (see section 6).
1.2. Each Parcel as a whole must be representative of the species and grade.
1.3. These grading rules define the poorest piece permitted in each grade; all other pieces, unless belonging to a lower grade, have to be included.
1.4. Except where stipulated, each piece shall be graded on the worse face.
1.5. Percentages are calculated in volume, unless specified otherwise.
1.6. As for parcels, quantity has to be within the limit of ± 10% of the volume with a maximum variation of 20 m3 (or 700 cubic feet). Nevertheless, in the case of fixed dimensions, quantity has to be within the limit of ± 5% of the volume with a maximum variation of 10 m3 (or 350 cubic feet).


SECTION 2 – STANDARD GRADES
2.1 First and Second Grade – (FAS)
Consists of not less than 40% clear of defects and sapwood, not more than 60% with defects within the limits set below, permitting clear sapwood not exceeding 10% of the width of the piece.
In an piece under 1.00 m² (less than 10 square feet) 1 defect
In an piece 1.00 m² to 1.50 m² (10 to 16 square feet) 2 defects
In an piece over 1.50 m² (over 16 square feet) 3 defects
This grade should be of good texture. A tolerance of 3% of volume of interlocked grain is allowed.
2.2 Number 1 Common and select Grade
Permitting defects within the limits set below, and clear sapwood not exceeding 20% of the width. This grade admits some variation in texture and grain.
In an piece under 0.60 m² (less than 6 square feet) 1 defect
In an piece 0.60 m² to 1.00 m² (6 to 10 square feet) 2 defects
In an piece 1.00 m² to 1.50 m² (10 to 15 square feet) 3 defects
In an piece over 1.50 m² (over 16 square feet) 4 defects

2.3 Number 2 Common Grade
Permitting clear sapwood without limit. Light to medium blue stain allowed. Permitting dead pinholes isolated and/or in clusters, not exceeding half of the surface of the piece, up to a maximum of 10% of pieces in one parcel. Abnormal grain is permitted, providing it does not materially affect the strength and flatness of the piece. Variations in colour and density permitted.
In an piece under 0.60 m² (less than 6 square feet) 1 defect
In an piece 0.60 m² to 1.00 m² (6 to 10 square feet) 2 defects
In an piece 1.00 m² to 1.50 m² (10 to 15 square feet) 3 defects
In an piece over 1.50 m² (over 16 square feet) 4 defects

SPECIAL GRADES
3.1 Prime Grade To be free of defects and sapwood for at least 80% and up to 20% with defects within the limits set below. Permitting clear sapwood not exceeding 5% of the width of the piece. In an piece under 1.00 m² (less than 10 square feet) 1 defect In an piece 1.00 m² to 1.50 m² (10 to 16 square feet) 2 defects In an piece over 1.50 m² (over 16 square feet) 3 defects This grade should be of excellent texture and free of abnormal grain.
3.2 Prime Narrows Grade The grain should be straight and free from defects.
3.3 First and Second (FAS) Shorts Grade c)
In specifications of 15 cm (6 in.) and wider, pieces de 20 cm (8 in.) and wider may include one defect. d) In specifications of 7.5 cm (3 in.) and wider, pieces de 15 cm (6 in.) and wider may include one defect.
3.4 Prime Strips Grade Better face to be free from defects, the reverse side and one third of the thickness of its adjacent edges admit one defect for each 1.20 m (4 ft) of length.

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