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Concrete Works

Concrete chemistry is simple: water + cement + aggregate + time = strength. But the ratio is everything. Too much water and your driveway cracks in 3 years. Too little and it won't pour. The difference between 0.45 and 0.60 water-cement ratio is 30% strength loss.

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Project Overview

schedule
Timeline
1-3 days for driveways/slabs; 5-10 days for foundations; curing takes 28 days for full strength
speed
Difficulty
Moderate for slabs and walkways; advanced for structural elements (footings, walls). Requires knowledge of mix design, finishing, and curing.
payments
Starting at
$2,500-$4,500
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Best Season
Best May-October. Concrete needs 10°C+ for curing. Winter pours require heated enclosures, insulated blankets, and accelerator additives.
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infoOverview

What is concrete works?

Concrete is a composite material: portland cement (the glue), aggregate (sand and gravel for bulk and strength), and water (activates the cement). When mixed, cement and water undergo a chemical reaction called hydration — this produces calcium silicate hydrate crystals that bind the aggregate into a solid mass. The reaction takes 28 days to complete; at 7 days you have ~75% of design strength, at 28 days you hit 100%.

Water-cement ratio is the most critical variable. Too much water makes the mix easy to pour but weakens the final product — every 0.05 increase in w/c ratio costs you ~5% in compressive strength. Industry standard for residential work is 0.45-0.50 (18-20 liters of water per 40 kg bag of cement). Contractors add extra water on hot days to keep the mix workable, but this destroys long-term durability.

Air entrainment is essential in Ontario. Freeze-thaw cycles (water freezes, expands 9%, cracks the concrete) destroy non-air-entrained concrete within 5-10 years. Air-entrained concrete has 4-7% microscopic air bubbles mixed in — these bubbles give the expanding ice somewhere to go, preventing cracking. You lose ~5% compressive strength, but you gain 10x the freeze-thaw durability.

Slump test measures workability. Pour a cone of concrete, remove the cone, measure how much it slumps. Target: 100-150 mm for most residential work. < 75 mm is too stiff (won't consolidate properly, leaves voids). > 175 mm is too wet (weak, prone to cracking). You can adjust slump with plasticizers (chemical admixtures that increase flow without adding water), but most ready-mix drivers just add water — easier but wrong.

Control joints prevent random cracking. Concrete shrinks as it cures (water evaporates, volume decreases). If the slab is restrained (tied to foundation walls, embedded rebar, or just friction with the subgrade), shrinkage creates tensile stress. Concrete is weak in tension; it cracks. Control joints are deliberate weak points — grooves cut or formed into the surface at 2-3x the slab thickness in feet. For a 4-inch slab, joints every 8-12 feet. The slab cracks at the joint (where you want it) instead of randomly across the surface.

Curing is more important than mix strength. A 25 MPa mix cured properly will outperform a 32 MPa mix cured poorly. Curing means keeping the concrete moist for 7 days minimum (14 days is better). Water is required for hydration; if the surface dries out, hydration stops and you get weak, dusty concrete. Methods: spray with water 3-4x per day, cover with wet burlap, or apply a curing compound (liquid membrane that traps moisture). Most contractors pour and walk away — the concrete looks fine, but it's 60-70% of design strength.

When you need concrete works

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    Pouring a new driveway or replacing a cracked/settled one (typical lifespan 20-30 years; shorter if not air-entrained or poorly drained)
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    Basement floor slab for new construction or after underpinning (4-6 inches thick, reinforced with 6x6 W1.4xW1.4 wire mesh)
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    Foundation footings for additions, garages, or new homes (width and depth per OBC Part 9 Section 9.15 — depends on soil bearing capacity)
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    Walkways, patios, or porch slabs (decorative options: stamped, exposed aggregate, or colored concrete)
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    Retaining walls or garden walls (require rebar, proper drainage, and frost-depth footings to prevent tipping or cracking)
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    Replacing deteriorated concrete steps (freeze-thaw damage, spalling, or rebar corrosion)
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    Repairing or resurfacing garage floors, basement floors, or commercial slabs (grinding, patching, or overlay with polymer-modified toppings)
timelineStep by Step

The Process

What happens from start to finish

1

Excavation and subgrade prep

0.5-1 day (depends on area and access)

Excavate to the required depth (depends on application — driveways need 6-8 inches of base + 4-6 inches of concrete; footings per OBC need to be below frost line, typically 4 feet / 1.2 m). Compact the subgrade with a plate compactor to prevent settlement. Install 4-6 inches of clear gravel base (3/4-inch stone) for driveways and slabs — this provides drainage and a stable base. Compact the gravel in 2-inch lifts.

2

Formwork and reinforcement

0.5-1 day

Build forms from 2x4 or 2x6 lumber, staked and braced to hold the concrete. Forms must be level (for slabs) or follow the designed slope (driveways need 2% slope for drainage). Install rebar or wire mesh per design — footings typically use #15M rebar at 400 mm O.C., slabs use 6x6 W1.4xW1.4 welded wire. Rebar must sit on chairs (plastic or metal supports) to position it in the middle third of the slab thickness.

3

Concrete placement

2-4 hours (depends on volume and crew size)

Order ready-mix concrete from a supplier — specify strength (25-32 MPa for residential), slump (100-150 mm), air entrainment (5-7%), and aggregate size (20 mm max for most jobs). Pour starts at the farthest point and works backward. Consolidate the concrete with a vibrator (removes air pockets) or by tamping with a 2x4. Screed the surface (drag a straight edge across the forms to level it). Work quickly — concrete starts setting in 60-90 minutes.

4

Finishing

1-2 hours

After screeding, wait for bleed water to evaporate (sheen disappears from surface). Float the surface with a bull float (smooths and levels). For driveways, use a broom finish (drag a stiff broom across the surface for traction). For interior slabs, trowel smooth with a steel trowel. Cut or form control joints at 2-3x slab thickness in feet (4-inch slab = 8-12 ft spacing). Edge the perimeter with an edging tool to round the corners (prevents chipping).

5

Curing

7-28 days

Keep the concrete moist for 7 days minimum. Methods: (1) spray with water 3-4x per day, (2) cover with plastic sheeting or wet burlap, or (3) apply a liquid curing compound (spray-on membrane). In hot weather (> 25°C), mist the surface hourly to prevent rapid evaporation. In cold weather (< 10°C), use insulated blankets or heated enclosures. Concrete gains 50% strength in 3 days, 75% at 7 days, 100% at 28 days — but only if kept moist.

6

Form removal and backfill

0.5 day

Remove forms after 24-48 hours (concrete is hard enough to support itself). Backfill around footings or retaining walls with graded fill, compacted in layers. For driveways, wait 7 days before light traffic, 28 days before heavy loads (trucks, RVs). Seal the surface (optional) with a penetrating sealer or acrylic coating to protect against deicing salts and moisture.

paymentsPricing Transparency

Investment Guide

Concrete is priced per cubic meter (m³) of material plus labor, forming, and finishing. Typical residential jobs range $150-$250 per m³ installed (includes labor, forming, placement, finishing, and curing). Structural work (footings, retaining walls) costs more due to rebar and engineering.

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Driveway (single-car, 10x20 ft / 3x6 m)

$2,500-$4,500

Depends on: Includes 4-6 inches of concrete, gravel base, wire mesh, broom finish, and curing. Stamped or colored concrete adds $3-$6 per sq ft. Removal of old concrete adds $800-$1,500.

Basement floor slab (1,000 sq ft / 93 m²)

$4,000-$7,000

Depends on: Includes 4 inches of concrete, 6x6 wire mesh, vapor barrier, and trowel finish. Does NOT include excavation, gravel fill, or weeping tile (those are separate line items).

Walkway or patio (100 sq ft / 9 m²)

$800-$1,500

Depends on: Includes 4 inches of concrete, gravel base, broom or smooth finish. Decorative finishes (stamped, exposed aggregate) add $5-$10 per sq ft.

Foundation footing (linear foot)

$40-$80 per linear foot

Depends on: Includes excavation, forming, rebar, and 25-32 MPa concrete. Width and depth depend on soil bearing capacity — engineer specifies. Frost-depth footings (4 ft deep) cost more than shallow footings (2 ft).

Retaining wall (per linear foot, 4-6 ft tall)

$150-$300 per linear foot

Depends on: Includes footing, rebar, wall forming, drainage (weeping tile behind wall), and backfill. Taller walls (6+ ft) require thicker walls, more rebar, and engineer review — pushes toward $400-$500 per linear foot.

Concrete steps (3-5 steps)

$1,200-$2,500

Depends on: Includes forming, rebar, 25 MPa concrete, and broom finish. Custom shapes, landings, or decorative finishes add 30-50%.

descriptionPermits
warningPermit Required
Building Permit (structural concrete)$200-$1,000
Grading and Drainage Plan (if altering site drainage)$500-$2,000
Engineered Drawings (for retaining walls > 4 ft)$1,500-$4,000

What Affects the Price

Concrete strength: 25 MPa is standard for driveways and slabs. 32 MPa is used for foundations and structural elements. Higher strength costs $5-$10 more per m³.Reinforcement: Wire mesh adds $0.50-$1 per sq ft; rebar adds $2-$5 per sq ft depending on spacing and size (#10M vs #15M).Finishing: Broom finish is standard (no extra cost). Smooth trowel finish adds $0.50-$1 per sq ft. Stamped concrete adds $8-$15 per sq ft. Exposed aggregate adds $5-$10 per sq ft.Thickness: Standard is 4 inches for slabs, 6 inches for driveways. Every additional inch adds ~$1.50 per sq ft.Access: If concrete trucks can't reach the site, you need a pump ($600-$1,200 per job) or wheelbarrows (doubles labor cost).Demolition: Removing old concrete costs $3-$6 per sq ft for breaking and hauling. Disposal fees add $100-$200 per load.Seasonal premiums: Winter pours require heated enclosures, insulated blankets, and accelerator additives — adds 20-40% to cost.

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Permits & Building Code

Ontario Building Code requirements

Permit / ApprovalAuthorityTypical Cost
Building Permit (structural concrete)City of Toronto or local municipality$200-$1,000
Grading and Drainage Plan (if altering site drainage)Municipal engineer or building department$500-$2,000
Engineered Drawings (for retaining walls > 4 ft)Professional Engineer (P.Eng)$1,500-$4,000

infoConcrete forming and placement do not typically require inspections unless part of a larger permitted project (e.g., foundation for a new build).

infoIf you're pouring a driveway that crosses a municipal sidewalk or boulevard, you need a Right of Way permit and must meet city standards for slope, width, and drainage.

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Concrete Works

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Formwork and reinforcement25%
Concrete placement30%
Final + Holdback30%

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$2,500-$4,500

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Concrete failures and how they happen

  • errorAdding water to increase slump: Drivers add water to make the concrete easier to pour, but every liter of extra water increases the w/c ratio and weakens the mix. A 0.60 w/c ratio (vs 0.45 design) loses 30% compressive strength. The concrete looks fine for 2-3 years, then starts cracking and spalling. You can't test strength after the fact — once it's poured, you're stuck with it. Specify slump on the delivery ticket and reject loads that are too wet.
  • errorPouring in freezing temperatures without protection: Concrete needs 10°C or higher for the first 3-7 days to cure properly. If it freezes during that window, ice crystals disrupt hydration and you lose 40-60% strength. The surface looks fine, but the concrete is weak and crumbly. Winter pours require insulated blankets, heated enclosures, or accelerator admixtures (calcium chloride) — budget an extra 20-40% for winter work.
  • errorSkipping air entrainment in Ontario: Non-air-entrained concrete fails in 5-10 years due to freeze-thaw damage. Water seeps into the concrete, freezes, expands 9%, and cracks the surface. This creates scaling (surface peeling off in layers) and spalling (chunks breaking off). Air-entrained concrete (4-7% air bubbles) gives the ice room to expand harmlessly. The bubbles reduce strength by ~5%, but they extend lifespan by 3-5x. Always specify air-entrained mix in climates with freeze-thaw cycles.
  • errorNo control joints or joints spaced too far apart: Concrete WILL crack as it shrinks — the question is where. Control joints create deliberate weak points so cracks form in straight lines (at the joint) instead of random zigzags. Rule of thumb: joint spacing = 2-3x slab thickness in feet. A 4-inch slab needs joints every 8-12 feet. If you skip joints or space them 20+ feet apart, you get random cracking within 1-2 years.
  • errorInadequate curing: Curing is keeping concrete moist for 7-28 days so hydration can complete. If the surface dries out, hydration stops and strength plateaus at 60-75%. The concrete is dusty, weak, and prone to surface cracking (crazing). Most contractors pour, finish, and leave — no curing compound, no wet burlap, no watering. Proper curing costs $100-$300 in materials/labor and adds 30-40% strength. Skipping it is the most common mistake.
  • errorThin slabs over poor subgrade: If the subgrade (soil under the slab) isn't compacted, it settles over 2-5 years and the slab sinks or cracks. Driveways need 4-6 inches of compacted gravel base; basement slabs need compacted fill or native clay. Contractors skip compaction to save time — you can't see it after the pour, but it causes settlement within 3-5 years. Always compact fill in 2-inch lifts with a plate compactor.
  • errorRebar too close to the surface: Rebar provides tensile strength, but it must be positioned correctly — middle third of the slab thickness. If it sits on the subgrade (bottom of slab), it doesn't resist bending. If it's too close to the surface (< 1 inch cover), moisture reaches the steel, it rusts, expands, and cracks the concrete (spalling). Use plastic or metal chairs to hold rebar at the correct height during the pour.
  • errorUsing deicing salts on new concrete: Salts (sodium chloride, calcium chloride) lower the freezing point of water, but they also cause scaling on concrete < 1 year old. The surface isn't fully cured and dense; salt brine penetrates and disrupts the hydration. Wait 1 year before using deicing salts on new driveways. Use sand for traction instead. After 1 year, apply a penetrating sealer to protect the surface.
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helpFAQ

Common Questions

What's the difference between 25 MPa and 32 MPa concrete?expand_more
MPa (megapascals) measures compressive strength — how much load the concrete can carry before crushing. 25 MPa = 3,600 PSI; 32 MPa = 4,600 PSI. Residential driveways, slabs, and walkways use 25 MPa. Foundations, footings, and structural elements use 32 MPa (or higher). The difference in cost is $5-$10 per m³. Stronger concrete is slightly more brittle, so it needs proper curing and jointing to avoid cracking.
How long do I have to wait before driving on a new driveway?expand_more
Light foot traffic: 24-48 hours. Cars: 7 days. Heavy trucks or RVs: 28 days (full strength). Concrete reaches 50% strength in 3 days, 75% at 7 days, 100% at 28 days. Driving on it too early creates surface cracking and indentations that are permanent. If you MUST use it early, lay plywood sheets to distribute the load.
Can I pour concrete in the rain?expand_more
Light rain is OK if the concrete has been placed and finished — cover it with plastic to prevent surface erosion. Heavy rain is a problem: it dilutes the surface, washes away cement paste, and weakens the top 1-2 inches. If rain is forecast within 2-3 hours of the pour, reschedule. Once concrete has cured for 24 hours, rain is actually beneficial (keeps it moist for hydration).
Why does my concrete have white powdery deposits (efflorescence)?expand_more
Efflorescence is salts (calcium hydroxide, sodium sulfate) dissolved by water migrating through the concrete and deposited on the surface when the water evaporates. It's cosmetic — you can brush it off or wash it with dilute vinegar. It indicates moisture is present, but it doesn't mean the concrete is weak. To prevent it: (1) use low-alkali cement, (2) cure properly to densify the surface, and (3) seal the concrete with a penetrating sealer.
What's the purpose of wire mesh in a slab?expand_more
Wire mesh (6x6 W1.4xW1.4 is standard) doesn't prevent cracking — it holds cracks together after they form. Concrete is weak in tension; it WILL crack as it shrinks. Wire mesh spans the crack and prevents it from opening wide (keeps it tight, < 1/16 inch). This maintains load transfer and prevents the slab from settling on one side of the crack. Rebar is stronger but more expensive; mesh is sufficient for non-structural slabs.
Can I patch concrete, or do I need to replace the whole slab?expand_more
Depends on the damage. Small cracks (< 1/4 inch) and spalls (< 1 inch deep) can be patched with polymer-modified repair mortars. Large cracks, settlement, or widespread spalling usually indicate subgrade failure — patching won't fix it, the slab will continue to fail. If > 30% of the surface is damaged, replacement is more cost-effective than patching. Grinding and overlays (1-2 inch polymer topping) are an option for surface damage without structural issues.
Why do driveways crack along the control joints?expand_more
That's EXACTLY what they're supposed to do. Control joints are deliberate weak points — grooves cut 1/4 to 1/3 the slab depth. Concrete shrinks as it cures; if it can't shrink (restrained by the subgrade or adjacent slabs), it cracks. Control joints give it a predetermined location to crack. The crack forms at the bottom of the groove (where the cross-section is thinnest) and is hidden by the joint. If cracks form BETWEEN joints, the joints are spaced too far apart.
What's stamped concrete, and is it worth the cost?expand_more
Stamped concrete is regular concrete imprinted with patterns (brick, stone, slate) using rubber mats while it's still wet. It's then colored with stains or integral pigments. Looks like high-end paving at 50-60% the cost. Downsides: (1) color fades over 10-15 years (needs resealing), (2) the surface is textured, so it's harder to shovel snow, and (3) cracks are more visible because they disrupt the pattern. Cost: $15-$25 per sq ft vs $6-$10 for plain concrete. If aesthetics matter and you're willing to maintain it, stamped concrete is a good value.
How do I design outdoor concrete steps properly?expand_more
Outdoor concrete steps follow a different formula than interior stairs. The ideal outdoor riser height is 5-7 inches (vs 7.5 inches indoors). The rule: one tread depth plus two riser heights should equal 25-27 inches. So a 6-inch riser needs a 13-15 inch tread — wider than interior stairs because you're wearing boots, carrying groceries, and dealing with rain and ice. To calculate: divide total rise (height difference) by your target riser height to get the number of steps — adjust until the riser falls in the 5-7 inch range. Treads must slope slightly forward (1/4 inch per foot of depth) so rain drains off instead of ponding and freezing. Concrete steps need a footing at the bottom; in Ontario, that footing goes below the frost line (4 feet / 1.2 m) to prevent heaving. At the top, anchor the steps to the existing structure with rebar or expansion strips.
What slope do walkways and patios need for drainage?expand_more
Every horizontal concrete surface needs slope — a perfectly flat slab ponds water, which freezes and causes spalling. Recommended slopes: walkways 0.5-5% (1/16 to 5/8 inch per foot), patios 1-2% (1/8 to 1/4 inch per foot). Use the formula D = G × L: D is total drop in feet, G is grade as a decimal, L is length in feet. A 25-foot patio at 1% grade: 0.01 × 25 = 0.25 feet (3 inches). So the low end of your patio should be 3 inches below the high end. Always slope AWAY from the house — water running toward the foundation causes basement moisture problems. For driveways, 2% slope is standard. Swales (shallow drainage ditches) along walkway edges handle heavy runoff: 1-10% slope depending on volume.
Do I need a vapor barrier under a basement slab?expand_more
Yes, always. Poly vapor barrier (6 mil minimum) goes under the slab to prevent moisture from wicking up through the concrete. Without it, the slab stays damp, which causes mold, musty smells, and flooring failures (laminate, carpet, hardwood all fail in damp environments). The poly goes on top of the gravel base, overlapping seams by 12 inches, taped at seams. Some contractors skip it to save $100-$200; you pay for it later in flooring replacements and air quality issues.
How thick should a driveway be?expand_more
Minimum 4 inches for light vehicles (cars, SUVs). 6 inches for heavy vehicles (trucks, RVs) or if the subgrade is soft (clay, fill). Thicker slabs cost more ($1.50 per sq ft per inch) but last longer and resist cracking. Some contractors pour 3-inch driveways to undercut competitors — these crack within 3-5 years under normal use. Always verify thickness BEFORE the pour (measure the forms) and DURING the pour (check depth with a ruler).
Where do expansion joints and control joints go in concrete?expand_more
Two types of joints, two different purposes. Expansion joints (isolation joints) separate your concrete from other structures — where a driveway meets the garage slab, where a walkway meets the house foundation, where a patio meets a porch. These joints use compressible material (asphalt-impregnated fiber board, foam strips) so the two slabs can expand and contract independently without cracking. Control joints (contraction joints) are intentional weak lines cut into the surface so that when the slab shrinks during curing, the crack follows the joint instead of forming randomly. Rule of thumb: control joints every 10-15 feet in driveways and every 4-5 feet in walkways. Joint depth should be at least 1/4 the slab thickness. Saw-cut within 6-12 hours of the pour (before the concrete cracks on its own). Missing or poorly spaced joints are the #1 reason driveways crack diagonally across the slab.
Can concrete be poured in cold or hot weather?expand_more
Yes, but with precautions. Cold weather (below 4°C / 40°F): water in the mix can freeze before concrete gains strength, creating ice crystal voids that permanently weaken it. Protect with heated mix water, accelerator admixtures, insulating blankets, and heated enclosures for critical work. Never let fresh concrete freeze in the first 48 hours. Hot weather (above 30°C / 85°F): rapid evaporation causes plastic shrinkage cracking, and accelerated hydration reduces working time. Counter with ice in the mix water, retarder admixtures, windbreaks, and curing compound applied immediately after finishing. The other rule: continuous pour. Once a slab or foundation pour starts, each truck must arrive within 30 minutes of the previous load. A gap longer than 30 minutes creates a cold joint — a weak seam where partially cured and fresh concrete meet. Cold joints crack and leak. Plan truck spacing with the batch plant before pour day.
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