At verges and side abutments, half slates must be used in alternate courses. Please note the half slates are sold in pairs, 1x left handed and 1x right handed half slate. A flat concrete slate which can be laid at pitches as low as 17.5. Our most economical concrete slate with interlocking edges for simple construction. An economical concrete slate, Mini Stonewold has interlocking edges ensuring quick and simple construction, reducing the laid cost of the roof. As with all of Redland's slate range, full compatibility with a range of dry-fix fittings and accessories gives additional peace of mind. Properties Nail size: 50mm x 3.35mm. Slate finish: smooth - through coloured. Certification BBA certified.