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BS EN 771-1 BS 3921 British Standard Specification for ...
www.websterbuildingsupplies.co.ukBS 3921 Size of Voids Solid bricks have no perforations or frogs. Perforated bricks have holes not exceeding 25% of the gross volume of brick. The area of any one hole should not exceed 10% and the amount of solid clay across the width should not be less than 30%. Frogged bricks may have depressions in one or