GRC Riven Promenade Flagstones 297mm x 297mm x 25mm - Cornish Slate Properties Compostion: Glass reinforced concrete. Dimensions: 297mm x 297mm x 25mm. Coverage: Approximately - 11 flagstones per m2. Weight: 4kg. Thermal resistance: 0.43. Description This riven finish is taken directly from original sedimentary sandstone blocks split along their natural cleavage planes. The resulting product offers several different patterns ensuring a naturally random effect is achieved every time. Eurodec GRC Promenade Flagstones are a specifically designed paving system to be loose laid onto paving support pads to provide an attractive, hardwearing surface to protect most flat roof waterproofing substrates from pedestrian traffic.