Everything you need to understand your concrete project

Glossary

Concrete terminology, explained plainly

Control joint

A saw cut or tooled groove that creates a weakened plane so shrinkage cracking happens where you planned it, below the surface, instead of randomly across the slab.

Isolation joint

Compressible material placed between a slab and a fixed structure - a foundation, column or wall - so the two can move independently.

Expansion joint

A joint that allows adjacent concrete sections to move without transferring load into each other. Often used at pool coping and long runs of flatwork.

Subgrade

The native or prepared soil the slab sits on. Its compaction and moisture condition govern how the finished slab performs more than almost anything else.

Base / aggregate base

Crushed rock placed and compacted over the subgrade to spread load and provide a uniform bearing surface.

Proof roll

Driving a loaded vehicle over a prepared base to reveal soft, yielding spots before concrete is placed over them.

PSI

Compressive strength of the cured concrete. Residential flatwork commonly specifies 3,500-4,000 PSI in this region.

Slump

A measure of how fluid the concrete mix is. Adding water on site to raise slump lowers strength and is a common cause of surface scaling.

Bleed water

Water that rises to the slab surface after placement. Finishing while bleed water is present traps it and produces a weak, dusty surface.

Curing

Keeping moisture available so the cement continues hydrating and gaining strength. Curing is not drying - it is the opposite.

Vapor retarder

A membrane under a slab that blocks moisture vapour from migrating up through the concrete, protecting flooring and coatings.

Expansive soil

Clay that changes volume with moisture content. Widespread in the Sacramento Valley and the main driver of seasonal slab movement here.

Spalling

Flaking or chipping of the concrete surface, usually from poor finishing, freeze damage or corroding reinforcement.

Scaling

Loss of the thin surface layer, almost always traceable to excess mix water, finishing over bleed water, or no cure.

Efflorescence

White crystalline deposit left when water moves through concrete and evaporates at the surface, carrying salts with it. Cosmetic, and usually a sign of a moisture path.

Doweling

Steel bars drilled and epoxied into existing concrete so a new pour transfers load across the joint instead of moving independently.

Rebar chairs

Small supports that hold reinforcing steel at the correct height within the slab. Without them, steel ends up on the bottom and does very little.

Broom finish

A textured surface created by dragging a broom across fresh concrete. The standard traction finish for driveways, walkways and patios.

Exposed aggregate

A finish where the surface paste is washed or ground back to reveal the stone in the mix. Durable, textured and cooler underfoot than dark finishes.

Densifier

A chemical applied during polishing that reacts inside the concrete to harden and close the surface, which is what makes polished floors abrasion-resistant.