Home

quality control

We applaud the professionalism of those in SAFCOL's silvicultural management who were responsible for the award by the of its certification for the forests which supplies Nicholson & Mullin, our flagship sawmill.

The South African Bureau of Standards (SABS) deserves much credit for the improvement in the quality of South African timber. In 1948 this body published the first specification for graded South African timber (SABS 5-1948). This specification applied to a number of timber products. The purpose was to encourage local sawmillers to grade to specification, to make good quality graded local timber available to the end user and to provide a guarantee of consistent quality.

The Department of Forestry, with the active co-operation of most sawmillers, imposed compulsory grading of structural timber in accordance with SABS 563 (now SANS 1783-2004). The application of the regulations was delegated to the SABS and this scheme ensures that only graded and marked structural timber of consistent quality reaches the consumer. The forestry act was repealed and the standards act was revised, allowing for other certification bodies to certify structural grades.

To make South African pine available in lengths exceeding 6,6 metres (which are the longest log lengths that local sawmills are normally designed to handle) and to make use of good quality short length timber of which large quantities are produced, much of it from dense, outer wood stems, finger jointing is used.

This method requires close factory control through all the processes of sawing, seasoning and grading of the raw material, followed by machining, gluing and curing of joints. The procedure for finger jointing is laid out in SANS 096-1976 - Code of Practice for the Manufacture of Finger Jointed Structural Timber.

The requirements of this code have been made mandatory in SABS 563 and SABS 1245. (now SANS 1783-2004). This ensures that finger jointed grade marked structural timber has been produced under compulsory quality control.

The structural mark, on the products of those manufacturers who have obtained the permission of their certification body to use it, guarantees that they have been manufactured under the quality control specification of the SANS. These measures continue to be exercised up to the time when the timber is despatched from the sawmill. A final check of warp must be made just prior to despatch and the timber should then be tightly bundled, well stacked in rail trucks or lorries and be well covered when leaving the mill.

Structural timber suitable for all normal building work is covered by SANS 1783-2004, which defines visual stress grades and mechanical stress grades (see table below for the mechanical properties of S5 and S7).

The SANS 1783-2004 code also covers timber used in furniture / appearance applications. Some of the major appearance grades available in South Africa are:

The compulsory grading of SANS timber prescribes that under grade structural sized timber is clearly marked with black crosses on both ends to distinguish it from graded timber bearing the appropriate SANS mark for the various visual grades. Crating and packaging grade is suitable for use in all timber applications where grading is not essential.

Graded finger-jointed structural timber has the letters FJ and the date of production stamped in black on the timber. The joints are glued with a Class 2 water-resistant clear glue.

In order to obtain the permissible stresses, grade stresses are adjusted by means of the appropriate modification factors which relate to the specific conditions of use.

Structural timber can be used to its full safe load -bearing capacity, and hence more economically, in engineered structures if it is stress-graded.

TABLE 4: Knot allowances in industrial grades.

Defect Sum of Sizes of all knots/ knot holes (see 2 below) in the worst 150mm length piece, max.
    Clear Grade Select Grade Furniture Grade Industrial Grade Crating Grade
a. Sound through face knots
( see 3 below)		 nil nil unlimited throughout 50% face unlimited 67% face unlimited 75% face
b. Edge knots:
( i ) On both edges judged together
( ii ) Individual size
nil

nil
nil

50% edge (see 4 below)
1 edge

75% edge
150% edge

100% edge
unlimited

100% edge
c. Full face splay knots nil nil nil unlimited unlimited
d. Knot whorls and knot clusters nil nil 67% face 100% face 100% face
e. All knots nil nil nil 100% face 100% face + 100% CAEE
f. Individual dead knots, loose knots, decayed knots, knot holes and knot cavities nil nil nil
( see 1 below)		 25% face 100% face
TABLE 5: Grade stresses for SA Pine, MPa

Nature of stress Grade of timber
  S5 S7
Bending 5.2 7.1
Tension parallel to grain 3.0 4.5
Tension perpendicular to grain 0.16 0.23
Compression parallel to grain 7.4 9.4
Compression perpendicular to grain* 2.1 3.0
Sheer parallel to grain 0.7 0.9
Modulus of elasticity 7800 9600

* Where slenderness value (l/b ratio) does not exceed 10

Care of timber before use

Timber is often unnecessarily exposed to deterioration on building sites due to the sun, rain and moisture, but this can be avoided by observing the following precautions:

Sizes of South African pine


mm 25 38 50 76 100 114 152 228
25       x   x x x
38   x x x x x x x
50       x     x x

Note: timber is sized by planing, leading to a 2mm reduction in thickness and 3mm reduction in width.

SABS Timber Specification for Softwood Timber: Products and Applicable Codes of Practice


Specifications by the South African National Standards.