NCCER Concrete Finishing key terms

A measurement of how much a fresh concrete sample settles when a standard cone is lifted off it, showing how wet or stiff the mix is.

A field procedure using a standard metal cone to measure concrete consistency; the drop in height of the sample after the cone is removed is recorded in inches or millimeters.

How easily fresh concrete can be mixed, placed, consolidated, and finished without segregating or bleeding, judged largely by feel and by slump.

The weight of water divided by the weight of cementitious material in a mix; lower values generally give stronger, denser, more durable concrete.

Separation of coarse aggregate from the mortar or paste, often caused by dropping concrete too far, over-vibration, or adding too much water.

Water rising to the surface of freshly placed concrete as heavier solids settle; excess bleed water weakens the top layer and can delay finishing.

Compacting fresh concrete to remove trapped air and voids, usually by internal vibration or spading, so it fully surrounds reinforcement and fills the forms.

A tool with a flexible shaft and vibrating head inserted into fresh concrete to consolidate it; it must be withdrawn slowly and not used to spread concrete.

A straightedge or mechanical tool drawn across the top of forms to strike off excess concrete and bring the surface to the required grade.

The act of removing surplus concrete from the surface by passing a straightedge or screed along the forms, leaving the slab at final elevation.

A wide, long-handled flat tool pushed across a freshly screeded slab to smooth the surface, push down aggregate, and open the surface for finishing.

A hand or power tool with a flat plate that works the surface of partially set concrete to embed aggregate and remove high and low spots before troweling.

A steel hand or power tool used on concrete that has stiffened, to produce a hard, dense, smooth surface; applying it too early draws water and weakens the top.

A large, long-handled finishing trowel, often used on large flatwork and bridge decks, that levels and smooths the surface with wide sweeping strokes.

A tool with a curved lip that rounds the outside edge of a slab to reduce chipping and create a neat, durable border.

A tool that cuts a straight, rounded groove in the surface to create a control joint that guides where the slab will crack.

A planned separation or groove in a concrete slab that allows movement, controls cracking, or marks a construction boundary between placements.

A sawed or tooled groove that creates a weakened plane so shrinkage cracks occur there instead of randomly across the slab.

A full-depth separation filled with a compressible material that lets adjacent concrete sections move without damaging each other.

A temporary or permanent structure that holds fresh concrete in place and shapes it until it hardens; forms must be sturdy, aligned, and treated with release agent.

A coating applied to the inside of forms so hardened concrete separates cleanly without sticking or damaging the surface.

A driven wooden or metal pin that holds forms, screed rails, or grade lines at the correct line and elevation during placement.

The planned elevation or slope of a concrete surface, set by stakes, forms, or laser levels and matched during screeding.

Keeping concrete moist and at a suitable temperature after placement so cement continues to hydrate and the concrete reaches its intended strength and durability.

A liquid sprayed on a fresh concrete surface that forms a film slowing moisture loss, used where wet curing or covers are impractical.

The chemical reaction between cement and water that hardens the paste and binds the aggregates into a solid mass; it continues for a long time after setting.

The stage when fresh concrete begins to stiffen and lose workability; finishing operations must be timed around it to avoid overworking the surface.

The stage when concrete has hardened enough that it can no longer be worked or finished; it marks the practical end of surface finishing.

Voids and exposed aggregate left in hardened concrete where mortar failed to fill spaces around aggregate, usually from poor consolidation or a mix that was too stiff.

Breaking or chipping away of concrete at edges, joints, or around reinforcement, often caused by poor finishing, corrosion, or freeze-thaw damage.

A narrow cut made with a concrete saw to form a control joint; timing matters because cutting too late allows random cracks to form first.

A slip-resistant texture created by dragging a stiff-bristled broom across concrete that has set enough to hold the grooves.

A decorative surface produced by removing the top layer of cement paste so the aggregate shows, using retarders, washing, or brushing at the right time.

Concrete textured with mats or stamps pressed into the surface while it is still workable to imitate stone, brick, or other patterns.

A plastic sheet placed under a slab to stop ground moisture from rising into the concrete and finished floor coverings.

Steel reinforcing bars placed in concrete to carry tensile forces; they must be covered by enough concrete and fully surrounded during consolidation.

The depth of concrete between the outer surface and the nearest reinforcement, protecting steel from moisture and fire.

Gear such as gloves, boots, eye protection, and knee pads worn to prevent cement burns, eye injury, and strain during concrete work.

Safe handling of concrete tools, including guarding power saws and trowels, disconnecting power before service, and keeping hands clear of moving parts.