Concrete Terms Every Homeowner Should Know

Materials and mix basics

• CementThe fine grey powder that acts as the binder. On its own it isn’t concrete — it’s one ingredient in it.
• ConcreteCement mixed with sand, aggregate (gravel or crushed stone), and water. This is what actually gets poured and hardens into a slab.
• MortarCement mixed with sand and water only — no coarse aggregate. Used for brickwork joints and plaster, not for pouring slabs.
• Portland cementThe standard type of cement used in most concrete, named after its resemblance to Portland stone, not a brand.
• AggregateThe gravel or crushed stone (coarse aggregate) and sand (fine aggregate) that make up the bulk of concrete’s volume and strength.
• AdmixtureA chemical added to concrete to change how it behaves — common ones speed up or slow down setting, increase workability, or add air entrainment.
• Ready-mixConcrete mixed at a plant and delivered wet by truck, priced and ordered by the cubic yard.
• Bagged concreteCement, sand, and aggregate pre-combined dry in a bag — add water and mix yourself.

Strength and mix design terms

PSI (compressive strength)

PSI stands for pounds per square inch, and it’s the standard way concrete strength is rated. Higher PSI means the concrete can bear more load before failing. This number is almost always tested at 28 days after pouring — concrete reaches roughly 65-75% of its rated strength by day 7, and the rest over the following three weeks.

Water-cement ratio

The ratio of water’s weight to cement’s weight in a mix — usually somewhere between 0.40 and 0.60. Lower ratios (less water relative to cement) produce stronger, denser concrete; higher ratios make the mix easier to work with but weaker once cured. Adding extra water on site to make a stiff mix easier to pour is one of the most common ways a project quietly loses strength.

Slump

A measurement, in inches, of how wet and workable a concrete mix is — tested by filling a cone-shaped mold with fresh concrete, removing the mold, and measuring how far the mix “slumps” down. A typical residential slump spec is around 4-6 inches. Higher slump means a wetter, easier-to-pour mix, but too much water reduces final strength.

Air-entrained concrete

Concrete with tiny, deliberately-introduced air bubbles (typically 4-7% of its volume) mixed in using an admixture. These bubbles give water room to expand when it freezes inside the concrete, which is what prevents the surface from cracking and flaking apart over repeated freeze-thaw cycles. It’s required for most outdoor concrete in climates that see winter freezing, and it does cost a small amount of strength in exchange for that durability.

Yield

How much finished volume a given amount of material produces — an 80 lb bag of concrete mix has a yield of about 0.60 cubic feet, for example. It’s the number that turns “how many bags” into “how much concrete.”

The pour and curing process

• Formwork (forms)The temporary boards or frames that hold wet concrete in its intended shape until it hardens enough to stand on its own.
• ScreedTo drag a straight board or tool across the top of freshly poured concrete, leveling it flush with the top of the forms.
• FloatA flat tool used right after screeding to smooth the surface and push larger aggregate slightly below the top layer.
• TrowelA tool used after floating for a smoother, denser final surface — steel troweling produces the smoothest possible finish.
• Broom finishDragging a broom across the surface before it fully sets, leaving light texture for traction. The standard finish for driveways and walkways.

Curing vs. drying — these are not the same thing

This is one of the most commonly mixed-up terms on the whole list. Drying is just water evaporating out of the concrete. Curing is the chemical reaction (called hydration) between cement and water that actually builds strength — and it needs the concrete to stay damp, not dry out, for that reaction to keep happening properly. Concrete that’s allowed to dry too fast cures poorly and ends up weaker and more prone to cracking, even though it looks perfectly “dry” and solid on the surface.

Set time

How long fresh concrete takes to go from a workable liquid to a solid that can’t be reshaped. Initial set is when it starts to stiffen and can no longer be finished; final set is when it’s hard enough to walk on carefully. Set time is different from cure time — a slab can be “set” within hours but still weeks away from its full 28-day strength.

Reinforcement terms

• RebarSteel reinforcing bars embedded in concrete to resist tension — concrete is strong under compression but weak under tension, and rebar covers that gap. Sized by number (a “#4 bar” is roughly ½ inch thick).
• Wire meshA welded grid of steel wire, lighter-duty than rebar, mainly used for crack control in patios and sidewalks rather than heavy structural support.
• Fiber meshSynthetic fibers mixed directly into the wet concrete rather than laid in a grid. Helps control fine surface cracking but doesn’t replace rebar for real structural loads.
• DowelA smooth steel rod placed across a joint between two slab sections, allowing them to move slightly without one section settling lower than the other.

Joints — the terms that confuse people most

All concrete cracks eventually — the real question is whether it cracks somewhere planned, or somewhere random. Joints are how contractors control that. Three of the four terms below are intentional; one is a mistake.

What’s under the slab

• Sub-base (or sub-grade)The compacted gravel layer placed under a slab before pouring, which spreads the load and improves drainage underneath.
• FootingA wider, deeper concrete base — usually 8-12 inches deep — that carries the weight of a wall, post, or column into the soil below the slab itself.
• Frost depth (frost line)How far below ground the soil freezes in winter, set by local climate. Footings need to sit below this line so the ground beneath them doesn’t heave when it freezes.
• Monolithic slabA slab and its footings poured together in a single continuous pour, with thicker edges to carry structural load — common for sheds, garages, and mild-climate foundations.

Common problems and what they look like

• EfflorescenceA white, chalky residue on the surface, left behind when water carrying dissolved mineral salts evaporates. Usually cosmetic, but persistent efflorescence can signal a moisture problem worth investigating.
• SpallingChunks of the surface breaking or flaking away, often from freeze-thaw cycles or corroding rebar pushing outward from inside the slab.
• ScalingThin flakes peeling off the surface, almost always from freeze-thaw damage in concrete that wasn’t properly air-entrained.
• HoneycombingA rough, rocky-looking surface with visible gaps around the aggregate, caused by air pockets that weren’t removed during the pour.

Ordering and measurement terms

• Cubic yardThe standard unit ready-mix concrete is sold by — equal to 27 cubic feet.
• Dry volumeThe larger volume of loose, unmixed materials needed to produce a given amount of finished concrete. Read the full breakdown in What is Dry Volume in Concrete?
• Waste factorThe extra percentage (typically 5-15%) added to a calculated volume to cover spillage, uneven ground, and material lost during mixing.
• Short loadA ready-mix delivery below the truck’s typical full or minimum load, which usually comes with an extra delivery fee.

The five terms worth knowing before any quote

1. PSI — match it to the project; don’t accept a lower rating than the use calls for.
2. Slump — a wetter mix pours easier but cures weaker.
3. Reinforcement type — wire mesh for light use, rebar for driveways and heavier loads.
4. Control joints — ask where they’ll be placed, since it affects how the slab will crack over time.
5. Curing — ask how the contractor plans to keep the slab damp for the first several days, not just how long it takes to dry.

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