S12

A heavier gauge sheet steel scraper for levelling and smoothing a surface that a polymer rib would flex away from. S12 is 152 mm (6 in), a long shallow D in a heavier gauge steel, so it is noticeably stiffer than the rest of the series.

S12 is a steel scraper. It is 152 mm (6 in), a long shallow D in a heavier gauge steel, so it is noticeably stiffer than the rest of the series. Steel holds its line where a polymer rib gives at the moment it meets resistance, so a scraper is the tool that actually gets a wall or a slab flat rather than merely smooth. Flex it between finger and thumb and it will follow a gentle curve; hold it stiff and it planes. Serrated versions exist in the same series if you want to score rather than level.