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PAS 70 - BS EN 777-1 - Technical Data - On-Site Testing Methods

On-Site Principle of Assessment

It is sometimes necessary to assess the acceptability of minor defects such as cracks, chips, surface blemishes and variation in texture of clay facing bricks when delivered to site.

It is suggested in PAS 70 that samples from deliveries of bricks are compared with a previously constructed reference panel of an appropriate size (not less than 1m²) and suitably located on site.

This reference panel should be representative of what can reasonably be expected to be delivered to site and should be large enough to encompass known and acceptable variations of colour and texture in the particular brick type.

Brick panels should be viewed from a distance of 3 metres, which is sufficient to reliably compare the aesthetic characteristics of the bulk delivery of facing bricks with the approved reference panel.

Guide to Technical Data

Size Tolerance

BS EN 777-1: requires a manufacturer to declare a particular size category for each product based on individual brick measurements. Different categories take into account the wide range of brick types and variation in acceptable appearance related to different manufacturing methods.

Size categories are based on formulae (to consider the differently sized products within EC Member States), and for the standard UK work sizes, the following table is applicable:

Notes: T2 bricks are classified as having the tightest tolerance. To determine the Tolerance applicable, measurements, using accurate instrumentation, are taken for each of 10 bricks sampled randomly from the consignment against their length, width, and height. The mean figure is calculated by addition of each specific measurement (for height two measurements in transverse directions are taken to provide an average), divided by 10. This figure should not deviate from the work size by the declared ( ) Tolerance category shown in Table 1. For a product of T2 tolerance, the mean figure for the length should therefore fall between 211mm and 219mm.

Range

The difference between the smallest and largest units, determined by the above test measurements, provides a figure for Range.

Different categories are based on formulae and for UK work sizes, Table 2 is applicable.

Notes: For a product of R1 range, the difference in length, for example, between the smallest and largest bricks tested should not exceed 9mm, and for classification the product must meet all requirements for the states category. For on-site measurement guidance please refer to the following section.

Useful on-site Guidance

As stated, product Standard BS EN 771-1: requires a manufacturer to declare a particular size category, based on individual brick measurements.

The use of delicate instruments is not practical however when dealing with issues on site, and in 2003 the British Standards Institution published a document suitable for on-site appraisal of brick units.

This Publicly Available Specification 70 (PAS 70), provides both guidance on appearance of facing bricks and practical on-site testing methods for size, using a conventional retractable steel rule as a viable alternative to the long jaw calliper method referred to in the European Standard.

PAS 70 has two procedures for measurement, the simpler of which (Procedure A), is used to determine the size tolerance of the brick consignment delivered to site.

10 individual bricks are selected at random from the consignment.

For determination of tolerance, bricks are set out on suitable level ground and the overall measurement taken for the 10 bricks as illustrated.

This overall dimension is then divided by 10 to provide the mean figure; this is rounded to the nearest whole number and the difference between this figure and the work size is compared to the Tolerance categories in Table 3.

Notes: The individual figures in PAS 70 are 1mm less than those in the European Standard BS EN 771-1 for each category (See Table 1) and appear to be more stringent. This allows for the recording of whole millimetres using a retractable steel rule, but provides sufficient confidence that the categories indicated by the on-site test would be confirmed by the more detailed measurement procedure set out in the European Standard.

PAS 70 also provides guidance on measurement of individual bricks should a dispute arise with regard to variation in individual brick sizes. Procedure B is used to determine the range, or difference between the smallest and largest bricks within the selected sample of 10 bricks.

Two measurements should be taken for each dimension, to provide a mean figure for each brick. The difference between smallest and largest units identified is compared with the Range category (see Table 4).

As with tolerance, the individual range figures in PAS 70 are 1mm less than those in BS EN 771-1 in each case, and for classification the product must meet all requirements for the stated category.

For more detailed or specific technical performance please contact our Design Services department at our Head Office: 0161 491 8200

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