S3

A flexible sheet steel scraper for levelling and smoothing a surface that a polymer rib would flex away from.

S3 is a steel scraper measuring 102 mm (4 in). 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.