screed

A screed is a long, rigid straightedge used to level and smooth freshly placed concrete, mortar, or other plastic materials across a defined surface. It typically spans the full width of the area being finished and rides on fixed supports (screeds or guides) set at the desired final level. The operator draws the screed across the wet material using a sawing or vibrating motion, cutting off excess and filling low spots in a single pass.

Screeds come in several forms suited to different tasks and scales. A straight screed is simply a rigid beam, usually aluminum or timber, used for small concrete pours or mortar beds. A vibrating screed contains an internal motor that oscillates the beam at high frequency, helping to consolidate concrete and produce a denser surface finish. Long screeds for large floor pours may be powered and self-propelled, riding on adjustable rails or laser-controlled support points that automatically maintain grade.

The name comes from an old sense meaning to cut or shred, reflecting the action of the tool shaving material flush with its supports. In bricklaying and stone work, a screed is also the thin mortar joint itself, laid to a uniform thickness and struck level. This usage, both the action and the result, appears in phrases like screeded bed or screed joint.

Proper screed technique directly affects floor flatness and slab quality. If the screed is lifted too quickly, low spots form; if dragged too slowly, it can fold material ahead of itself. On large pours, the screed must be checked regularly for wear or damage to the striking surface, as dents or warping create ridges in the finished concrete. Many specifications now call for flatness tolerances measured after screeding, often expressed as deviation per 10 feet or 3 meters.

Screeds are essential to concrete flatwork, toppings, and mortar applications from single-story buildings to multi-story construction. They sit downstream of the initial pour or placement but upstream of further finishing, troweling, brooming, or grinding, so their accuracy sets the baseline for all subsequent work.