BS EN 12326: Part 1: 2004
The new European standard for roofing slate - BS EN 12326: Part 1: 2004, has recently come into effect and replaces the old BS 680: Part 2 (1971).
This standard has caused some confusion in the marketplace and, in order to clarify the standard, we have summarized the main points of the new standard below:
Dimensions
Tolerances are provided for length, width, individual thickness, flatness, squareness (or rectangularity) and edge deviation. The packed thicknesses for 100 slates must be determined for every pallet to allow the calculation of the average roofing slate thickness, with a reduction applied based on the surface finish
Flexural Strength
Test samples are supported on two bars and a third central bar is pushed down until failure occurs. The test is carried out both parallel and perpendicular to the long edge of the roofing slates. The characteristic modulus of rupture is calculated and the larger of the two values is used for calculating the minimum individual thickness of the roofing slate. Large differences may indicate a grain or secondary splitting direction.
Water Absorption
Samples are dried to constant weight and then immersed in water. The absorption is determined from the difference in mass. Values less than 0.6% are classed as A1 while those above 0.6% are classed as A2.
Freeze-thaw test
Only required for Class A2 roofing slates. 100 cycles of freezing in air and thawing in water, and the flexural strength test is repeated. If there is a significant change, the slate should not be used
Non-carbonate carbon content
This determines the amount of graphite present, along with oils and other organic matter. If the slate has in excess of 2% graphite content, it fails the test.
Carbonate Content
These groups are classified which are the used to apply factors for increasing the determined thickness of the slate. The carbonate content is also used to dictate the method of sulphur dioxide testing.
Sulphur dioxide exposure for slate with less than 20% carbonate
Test samples are exposed to sulphur dioxide at two different concentrations for 21 days. Depending upon changes during the test, one of 3 codes may be given. The code is the used to apply a thickness adjustment depending on whether the slate has less than 5% or 5-20% carbonate.
Sulphur Dioxide exposure for slates with more than 20% carbonate
Test samples are subjected to surface scraping before and after exposure to sulphur dioxide vapour with the increase in material scraped after exposure taken to be the depth of softening. A thickness adjustment is applied to all slates unless the softened layer is greater than 0.7mm, when the slate is not considered to be suitable for roofing or cladding purposes.
Thermal Cycle Test
Test samples are subjected to 20 cycles of immersion in water followed by drying at 110 degrees celcius, after which they are inspected for the presence of potentially deleterious mineral components. Three codes are applied as follows: Code T1 for slates with colour changes that neither affect the structure nor form runs of discolouration; Code T2 for slates with colour runs that do not cause structural changes; and code T3 for slates where holes may be formed from the oxidization of inclusions. If exfollation, splitting or other structural changes occur, the roofing slates are considered unacceptable for use.
Petrographic examination
Geological appraisal that may involve optical microscopy, X-ray diffraction and scanning electron microscopy. The examination is important to classify the roofing slate and also to determine the presence of potentially deleterious structures or minerals.