Concrete Placement, Finishing & Curing

Concrete is unforgiving. Once the trucks start rolling, the clock is ticking, and there’s no pause button. Placement, finishing, and curing are a continuous chain of operations — mess up one link and you’ll see it in the slab for the next fifty years. This guide covers skills 2.08 through 2.18: everything from the moment concrete leaves the chute to the day you strip the forms and admire your work (or curse it).

1. Placement by Boom Pump — Skill 2.08

The boom pump is the workhorse of modern concrete placement. A truck-mounted articulating boom can reach 32 m to 63 m, placing concrete exactly where you need it without the crew dragging hoses all over the site. On a typical church foundation pour, the boom pump is the default choice.

Setup & Pipeline Layout

1. Outrigger pads: The pump truck deploys outriggers that exert enormous ground pressure — up to 50 tonnes per pad. Always use timber mats or steel plates under pads. Never set up on a backfilled trench, near an excavation edge, or on soft ground without engineered cribbing.
2. Boom swing radius: Map the boom’s full swing radius before the pour. Confirm clearance from overhead power lines (minimum 3 m for lines under 750 V per O. Reg. 213/91, s. 188). The pump operator will verify, but it’s your site — own the safety.
3. Priming the line: Before concrete flows, the pump line must be primed with a slurry of cement and water (or a commercial primer). This lubricates the pipe walls and prevents the first batch from plugging. Collect the primer slurry in a wheelbarrow — do not dump it into the forms.
4. End-hose length: Keep the flexible end hose to 3 m maximum. Longer hoses whip dangerously when concrete surges. Two crew members should control the end hose at all times.

Communication & Pour Rate

Clear communication between the placement crew and the pump operator is strongly recommended. Establish hand signals or radio protocol before the pour begins:

• Go / pour: One arm raised, fist pumping
• Slow down: Palm-down, patting motion
• Stop: Both arms crossed overhead
• Swing left / right: Arm extended in direction of desired swing

Typical pour rates for a boom pump range from 60 – 150 m³/hr, depending on mix design, slump, and pipeline distance. For a 150 mm church slab on grade, you’re looking at roughly 10 – 12 m³ per truckload, with trucks cycling every 15 – 20 minutes. Coordinate with the batch plant to keep trucks flowing steadily — gaps create cold joints.

Avoiding Cold Joints

A cold joint forms when fresh concrete is placed against a previous lift or section that has already begun to set. The bond between the two layers is compromised, creating a potential crack plane and water pathway. Per CSA A23.1, Clause 7.4.2, concrete must be placed in a continuous operation, with each layer deposited before the preceding layer has taken initial set (typically 60 – 90 minutes depending on temperature and admixtures).

2. Placement by Line Pump — Skill 2.09

A line pump (also called a ground-line or trailer pump) pushes concrete through steel pipes and rubber hoses laid along the ground. It’s the right tool when the boom pump is overkill — or can’t reach.

When to Choose a Line Pump

• Interior work: Basement slabs, topping slabs, elevator pits — anywhere a boom can’t swing overhead
• Long horizontal runs: Pipelines can extend 150 m+ with steel reducers and elbows
• Smaller pours: Under 20 m³ where mobilizing a boom pump isn’t cost-effective
• Restricted sites: Tight urban lots where the boom truck simply can’t set up

Limitations & Hose Management

Line pumps typically deliver 15 – 60 m³/hr — slower than a boom. Every 90° elbow in the pipeline adds the equivalent of roughly 3 m of horizontal run in friction loss. The mix design matters too: line pumps struggle with low-slump concrete (below 80 mm) and mixes with large aggregate (over 20 mm).

Secure all pipe joints with clamps — a blowout under 15 MPa of pump pressure can send a fitting through a wall. Lay pipelines on a gradual curve rather than sharp bends. At the discharge end, use a minimum 3 m flexible hose for manoeuvrability, and have at least two crew members controlling it.

3. Placement by Crane & Bucket — Skill 2.10

When you can’t pump — maybe the mix is too stiff, the aggregate is too large, or the pour location is 30 storeys up — you go old school: crane and bucket. This method is slower but handles virtually any concrete mix.

Rigging & Equipment

• Bucket sizes: Typically 0.5 m³ to 2.0 m³. A 1.0 m³ bucket of normal-weight concrete weighs approximately 2,400 kg — confirm your crane’s capacity at the working radius.
• Gate mechanism: Buckets use a lever-operated or cable-operated bottom gate. Inspect the gate seal before every pour — a leaking gate dripping concrete across the site is embarrassing at best, dangerous at worst.
• Rigging: The bucket hangs from the crane’s main hook via a bail or shackle. Never side-load the hook. Ensure the bail is centred so the bucket hangs plumb.

Signal Person & Placement

A designated signal person is mandatory per O. Reg. 213/91 for all crane operations. Use CSA Z150 standard hand signals. The signal person controls all bucket movements — the crane operator does not swing, hoist, or open the gate without a clear signal.

Place concrete as close to its final position as possible. Do not drop concrete from more than 1.5 m to avoid segregation. For deep pours (walls, columns), use a tremie pipe or elephant trunk to guide the concrete down without free-fall.

4. Direct Chute Placement — Skill 2.11

Sometimes the simplest method is the best. If the truck can get close enough, pouring directly down the chute is fast, free, and surprisingly effective. No pump to clean, no bucket to rig, no extra equipment to rent.

Truck Positioning & Chute Extensions

A standard ready-mix truck chute reaches about 3.5 m from the rear of the truck. With bolt-on chute extensions, you can stretch that to roughly 5 – 6 m. Beyond that, you’re asking for trouble — the concrete won’t flow uphill, and the chute angle becomes too shallow to maintain flow with anything under 150 mm slump.

Position the truck so the driver can back in straight. Chute swing is limited to about 180° at the rear of the drum. The truck driver controls drum speed and can slow or stop the pour, but give them clear signals — they can’t always see where the concrete is landing.

5. Vibration & Consolidation — Skill 2.12

Concrete straight out of the truck is full of trapped air — sometimes 5 – 15% voids by volume in a low-slump mix. Vibration consolidates the concrete, forcing out trapped air and ensuring the mix fills every corner of the formwork. Done right, you get dense, strong, durable concrete. Done wrong (or not at all), you get honeycombs, bug holes, and a slab that looks like Swiss cheese.

Internal (Pencil) Vibrator Technique

The internal vibrator — a.k.a. the pencil vibrator, stinger, or poker — is the most common consolidation tool on site. Here’s how to use it properly:

1. Insert vertically (or as close to vertical as possible) at a rapid, steady pace. Let the vibrator sink under its own weight — don’t force it.
2. Penetrate the previous lift by 75 – 150 mm to knit the two layers together.
3. Hold for 5 – 15 seconds per insertion until a thin sheen of paste appears on the surface and large air bubbles stop rising.
4. Withdraw slowly at approximately 75 mm per second to allow the hole to close behind the head.
5. Move to next insertion point at a spacing of 1.5 times the vibrator’s radius of action.

Vibration Radius by Head Diameter

Over-Vibration Risks

More is not always better. Over-vibrating causes segregation — the heavy aggregate sinks and the paste and water rise to the top. Signs of over-vibration include excessive surface paste, a “soupy” appearance, and aggregate visible settling away from the surface. Over-vibrated concrete can also blow out formwork if the lateral pressure exceeds the form’s design capacity.

External Form Vibrators

For walls, columns, and other formed elements, external vibrators (mounted to the outside of the formwork) supplement internal vibration. They’re especially useful for architectural concrete where surface quality matters. Mount them at 1.0 – 1.5 m centres vertically, staggered on opposite form faces, and operate them for 30 – 60 seconds per cycle as each lift is placed.

6. Screeding & Bull Floating — Skill 2.13

Once concrete is placed and vibrated, screeding strikes off the excess and establishes the slab elevation. Bull floating follows immediately to close the surface and push down aggregate. These two operations set up everything that follows — if the screed is off, the finish will be off.

Wet Screed vs. Laser Screed

Wet screed (manual): A straightedge (aluminum or magnesium, typically 2.4 – 4.8 m long) pulled across the surface, riding on preset screed rails or the top of the forms. Two crew members pull the screed with a sawing motion while advancing forward about 25 mm per stroke. Keep a roll of excess concrete ahead of the screed — this fills low spots.

Laser screed (machine): A self-propelled machine (like the Somero S-485) that uses a laser-guided head to screed, vibrate, and float in a single pass. Accuracy is ±3 mm over a 3 m straightedge. Laser screeds are cost-effective on large slabs (500 m²+) and deliver floor flatness numbers (FF/FL) that manual screeding can’t match. On large church sanctuary slabs, laser screeding is preferred whenever access allows.

Bull Floating

The bull float is a large flat blade (typically 1.2 m × 200 mm) on a long handle, used immediately after screeding. Push the float away from you with the leading edge slightly raised, then pull it back flat. This embeds aggregate, fills voids, and creates an initial smooth surface. Timing is critical — bull float while the surface is still glistening wet. If bleed water is pooling, wait for it to absorb before floating.

Magnesium vs. wood floats: Magnesium floats are lighter, smoother, and don’t absorb water. They’re the standard for most finishing. Wood floats drag more aggressively and are useful for pulling paste to the surface on dry or stiff mixes — but they can tear an air-entrained surface if used too aggressively.

7. Power Trowelling — Skill 2.14

Power trowelling transforms a rough, bull-floated surface into a hard, dense, burnished finish. It’s part art, part science, and entirely about timing. Start too early and you’ll tear the surface. Start too late and the concrete fights you.

Walk-Behind vs. Ride-On

Walk-behind trowels (36″ – 48″ diameter) are used on smaller slabs, edges, and around penetrations. One operator walks behind the machine, controlling pitch and direction through the handles. Great for detail work and areas a ride-on can’t reach.

Ride-on trowels (twin-rotor, 72″ – 96″ span) cover massive areas quickly. On a 1,000 m² church slab, a ride-on can achieve a hard-trowel finish in a fraction of the time. Operators sit on the machine and control each rotor independently via joystick. These machines require experience — a novice on a ride-on will leave swirl marks, edge gouges, and regret.

Timing Based on Bleed Water

The number one rule of power trowelling: never trowel bleed water back into the surface. Bleed water is excess mix water rising to the top as the concrete consolidates. Trowelling it in creates a weak, dusty surface layer that will delaminate and scale. Wait until the bleed water sheen disappears and the concrete supports your weight with only a slight impression (~ 5 mm footprint) before starting the float pan pass.

Common Defects

• Burn marks: Dark streaks caused by trowelling too aggressively on stiff concrete. The blades generate friction heat that discolours the paste. Reduce blade pitch or speed.
• Delamination: A thin surface crust separates from the slab body — usually from trowelling over bleed water or finishing air-entrained concrete too aggressively. Air-entrained exterior concrete should generally not receive a hard-trowel finish.
• Swirl marks: Visible circular patterns from inconsistent trowel speed or uneven blade wear. Keep blades in matched sets and replace when worn beyond 1 mm variation.

8. Broom Finishing — Skill 2.15

Not every slab needs a mirror finish. Sidewalks, ramps, exterior slabs, and loading docks all need texture for slip resistance. That’s where the broom comes in — the most humble and underrated tool in the finisher’s kit.

When to Broom

Brooming happens after bull floating (or a light float-pan trowel pass) but before the surface is too stiff to accept texture. The concrete should be firm enough that the broom bristles leave defined grooves without tearing chunks of aggregate out of the surface. Typically, this window is 30 – 90 minutes after bull floating, depending on temperature and mix design.

Brush Types & Texture Depth

• Soft-bristle broom: Produces a fine, light texture (0.5 – 1.0 mm depth). Suitable for covered walkways and light-traffic areas.
• Medium-bristle broom: Standard for most exterior flatwork (1.0 – 2.0 mm depth). Good slip resistance without being aggressive on bare feet (important for church entrances in summer).
• Stiff-bristle / horsehair broom: Deep, aggressive texture (2.0 – 3.0 mm). Used on ramps, loading docks, and steep sidewalks.

Always pull the broom in one direction — perpendicular to the direction of traffic flow. This channels water off the surface. Use long, even strokes without stopping mid-pull, and rinse the broom frequently to prevent paste buildup that clogs the bristles and leaves inconsistent texture.

9. Concrete Curing — Skill 2.16

Curing is the most neglected step in concrete construction. Everyone’s excited about the pour, the finishing looks great, and then … the crew moves on and nobody thinks about moisture retention. But curing is where concrete develops its strength. Skip it, and you’re leaving 30 – 40% of the concrete’s potential strength on the table.

Why Curing Matters

Cement hydration requires water. If the surface dries out prematurely, hydration stops and the surface layer becomes weak, dusty, and prone to cracking. CSA A23.1 requires that concrete be cured to achieve a minimum of 70% of specified 28-day strength before exposure to freeze-thaw cycles (Clause 7.7).

Curing Methods

1. Curing compounds (most common):

• Dissipating type (CSA A23.1 / CAN/CGSB 1-GP-19Ma Type 1): Applied to fresh concrete, breaks down within 30 days. Good when a bonded topping, adhesive, or coating will follow — the compound must be gone before the next material goes down.
• Non-dissipating type (CSA A23.1 / CAN/CGSB 1-GP-19Ma Type 2): Designed to remain on the surface permanently. Used on exterior slabs, roads, and surfaces that won’t receive coatings. Typically white-pigmented to reflect heat.
• Application rate: 5 m² per litre, applied in two passes at right angles immediately after final finishing. Do not spray over bleed water — it will trap the water and cause scaling.

2. Wet burlap: Lay pre-wetted burlap sheets over the surface immediately after finishing. Keep burlap continuously wet for the entire curing period. This is the gold standard for critical structural elements but labour-intensive.

3. Polyethylene sheeting: 0.15 mm (6-mil) poly laid over the surface with edges weighted or taped. Traps moisture effectively but can cause discolouration where the poly contacts the concrete (mottling). Not recommended for architectural surfaces.

4. Water curing (ponding / misting): Continuous water application or ponding on flat surfaces. Excellent for large slabs in hot weather. Requires constant monitoring — if the water supply is interrupted and the surface dries, rapid shrinkage cracking can result.

Minimum Curing Times — CSA A23.1, Table 19

Hot Weather Curing (> 27 °C)

In hot weather, evaporation rate can exceed bleed rate, causing plastic shrinkage cracking within the first hour. Use evaporation retarders (spray monomolecular film), erect wind breaks, and begin curing immediately after finishing — do not wait. CSA A23.1, Clause 7.7.3 requires special precautions when the evaporation rate exceeds 1.0 kg/m²/hr.

Cold Weather Curing (< 5 °C)

Concrete must be maintained above 10 °C for the first 72 hours per CSA A23.1, Clause 7.7.4. Use insulated blankets, heated enclosures, or hydronic heating. Never let fresh concrete freeze — ice crystal formation in the paste destroys the microstructure permanently. Concrete that freezes within the first 24 hours can lose 50% of its ultimate strength.

10. Sawcutting Control Joints — Skill 2.17

Concrete is going to crack. That’s not pessimism — it’s physics. Drying shrinkage, thermal contraction, and subgrade restraint all conspire to pull the slab apart. Control joints don’t prevent cracking; they control where the crack occurs by creating a weakened plane where the concrete will crack in a straight, predictable line instead of wherever it pleases.

The Timing Window — This Is Critical

Sawcutting has a very narrow window. Cut too early and the blade ravels the aggregate out of the fresh concrete, leaving a ragged, ugly joint. Cut too late and the concrete has already cracked somewhere else — and you’re sawcutting for nothing.

For early-entry saws (Soff-Cut type with a small, thin blade and skid plate), you can cut as early as 4 – 6 hours after placement — as soon as the surface can support the saw without scuffing. These are the preferred tool for most church slab work because they let you get in early and stay ahead of cracking.

Cut Depth & Spacing

• Depth: Minimum 1/4 of the slab depth for early-entry saws; 1/3 of slab depth for conventional wet saws. For a 150 mm slab, that’s 38 – 50 mm deep.
• Spacing: Maximum joint spacing is 24 – 36 times the slab thickness. For a 150 mm slab: 3.6 – 5.4 m maximum spacing. The common rule of thumb is panels no longer than 4.5 m per side for a 150 mm slab.
• Aspect ratio: Keep panels as close to square as possible. The length-to-width ratio of any panel should not exceed 1.5:1. L-shaped and T-shaped panels will crack at the re-entrant corners.

11. Form Stripping — Skill 2.17a

Stripping forms too early is one of the most common — and most expensive — mistakes on a concrete job. The concrete may look hard on the surface, but the interior may still be developing the strength needed to support the loads that stripping introduces (self-weight, construction loads, reshoring loads).

Minimum Strength Requirements — CSA A23.1, Table 21

Cold weather adjustments: At 5 °C, strength development takes roughly twice as long as at 20 °C. At 0 °C, hydration essentially stops. Use maturity metering or field-cured cylinders — not calendar time — to verify strength before stripping in cold weather.

Stripping Procedure

1. Verify strength by field-cured test cylinders or maturity testing.
2. Remove ties, wedges, and external bracing first.
3. Strip forms by carefully prying away from the concrete face using form bars. Never use a claw hammer on the concrete surface — you’ll gouge it.
4. Begin at the top and work down so forms don’t fall away under their own weight and damage the concrete below.
5. Leave reshoring in place as required by the structural engineer’s reshoring plan. Never remove shoring under a multi-storey structure without engineering approval.

12. Concrete Patching & Repair — Skill 2.18

In a perfect world, every pour would come out flawless. In the real world, you’re going to strip forms and find honeycombs, bug holes, tie holes, and the occasional mystery void. Proper patching restores the concrete’s structural integrity and appearance — bad patching makes it look worse than the original defect.

Common Defects & Repairs

Honeycombs: Voids where paste didn’t fill around the aggregate, usually caused by inadequate vibration or mix segregation. For shallow honeycombs (< 25 mm), chip out loose material, dampen the area, and pack with a stiff repair mortar (1:2.5 cement-to-sand, or a proprietary non-shrink grout). For deep honeycombs (> 25 mm), the structural engineer must assess before repair — these may require epoxy injection, formed repair, or even removal and replacement.

Bug holes (surface voids): Small air bubbles (1 – 15 mm) trapped against the form face. These are cosmetic on formed surfaces and can be filled with a cement-paste rubbing compound during surface rubbing (see below). On architectural concrete, specify form-release agents that minimize bug holes and use external vibrators.

Tie holes: The round voids left by form-tie cones or snap-tie breakbacks. Clean the hole, dampen, and fill with non-shrink grout or a proprietary tie-hole repair plug. On below-grade walls, tie holes must be sealed with a waterproof mortar or mechanical plug to prevent water infiltration.

Surface Rubbing

Surface rubbing (or “sacking”) is the process of applying a thin cement-paste slurry over formed concrete surfaces to fill bug holes, small imperfections, and form marks. Mix Portland cement with fine sand (1:1 to 1:2 ratio) to a thick paste. Dampen the concrete, then rub the paste into the surface using a burlap pad or rubber float in a circular motion. Immediately wipe off excess with clean, damp burlap. The result should be a uniform, smooth surface with all voids filled and no paste buildup.

Putting It All Together

Concrete placement, finishing, and curing are a relay race. The boom pump operator hands off to the vibrator crew, who hands off to the screed team, who hands off to the finishers, who hand off to the curing crew, who hand off to the saw team. Every handoff is a potential failure point, and every failure shows up in the finished product — permanently.

The difference between a mediocre concrete crew and a great one isn’t talent. It’s preparation. Know your pour rate. Pre-calculate your truck spacing. Lay out your joints on paper. Check the weather forecast. Brief the crew. Have backup equipment on site. And never, ever skip the curing.

These aren’t just skills — they’re the foundation of every church construction project. Literally.