Red Seal Concrete Finisher flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Silica exposure limit

The permissible exposure limit for respirable crystalline silica is often 0.025 mg/m³ over an 8-hour shift; wet cutting and dust collection are required to stay below this.

Concrete burn first aid

Wet cement is alkaline and can cause severe burns; immediately wash affected skin with clean water, remove contaminated clothing, and seek medical attention for persistent irritation.

Trench shoring threshold

Trenches deeper than 1.2 m (4 ft) generally require shoring, sloping, or a trench box; spoil piles must be kept at least 1 m (3 ft) from the edge.

Washout water disposal

Concrete washout water must be contained in a designated pit or tank and never discharged to storm drains; neutralize pH before disposal according to local sewer bylaws.

Vibrator head selection

Choose a vibrator head diameter of 25–40 mm for thin walls and 50–75 mm for mass concrete; frequency should be 10,000–15,000 vpm, and never use it to move concrete laterally.

Bull float purpose

A bull float is used immediately after screeding to open the concrete surface, embed aggregate, and remove high spots; keep the tool flat and avoid overworking the surface.

Groover depth rule

Control joints should be cut to a depth of at least 1/4 of the slab thickness, with a minimum of 25 mm, to ensure cracking occurs at the joint.

Power trowel blade pitch

Adjust blade pitch from flat for floating to angled for burnishing; increased pitch and speed produce a denser, smoother finish but can cause delamination if overdone.

Subgrade compaction tolerance

Slab subgrade should be compacted to typically 95% Standard Proctor density and finished to ±10 mm (3/8 in) tolerance; proof-roll to detect soft spots.

Control joint spacing

Space control joints at 24–36 times the slab thickness (e.g., 100 mm slab → 2.4–3.6 m); keep panel aspect ratio ≤1.5:1 and align joints with re-entrant corners.

Vapor barrier thickness

Under interior slabs, use 10–15 mil (0.25–0.38 mm) polyethylene vapor barrier; lap joints 150 mm and tape; seal all penetrations to prevent moisture migration.

Formwork lateral pressure formula

For normal concrete, lateral pressure can be estimated as p = 72 + 7800R/(T+18) kPa, where R is pour rate (m/h) and T is concrete temperature (°C); use ACI 347 for design.

Form removal timing

Side forms can typically be removed after 24–48 hours when concrete can resist damage; soffit forms and shores must remain until concrete reaches design strength, often 70–100% of f'c.

Form tie spacing

Form ties are typically spaced 600–900 mm (2–3 ft) on center both horizontally and vertically, depending on lateral pressure; ensure ties are tight and washers are in place.

Rebar size 15M area

A 15M metric rebar has a nominal diameter of 15 mm and a cross-sectional area of 200 mm²; it is roughly equivalent to a #5 imperial bar (area 200 mm²).

Typical slab cover

For slabs on grade not exposed to weather, typical concrete cover over reinforcement is 20 mm (3/4 in); increase to 40–50 mm for surfaces exposed to earth or weather.

Tension lap splice length

For Grade 420 (60 ksi) rebar in normal-weight concrete, tension lap splices are often 40 bar diameters; stagger laps and verify with CSA A23.3 or ACI 318.

Vibrator insertion spacing

Insert the vibrator vertically at spacing not exceeding 1.5 times its radius of action (typically 400–600 mm), and penetrate the previous layer by 100–150 mm.

Concrete free-fall limit

To prevent segregation, limit free fall of concrete to 1.5 m (5 ft) unless using a chute or tremie; place in horizontal layers of 300–500 mm.

Hot weather placement limit

Avoid placing concrete when ambient temperature exceeds 30°C (86°F) if possible; use chilled water or ice, and cure immediately to prevent plastic shrinkage cracking.

Cold weather protection

Maintain concrete temperature above 5°C (40°F) during placement and curing; use heated enclosures or insulated blankets, and never place concrete on frozen subgrade.

Curing duration

Cure normal Portland cement concrete for at least 7 days; use 3 days for high-early strength cement; extend to 14 days for cold weather or blended cements per project specifications.

Curing compound application

Apply liquid membrane-forming curing compound immediately after finishing when the surface is no longer glossy, usually within 30 minutes; follow manufacturer coverage rate, often 5 m²/L.

Plastic sheeting curing

Cover concrete with 0.1 mm (4 mil) polyethylene sheeting, overlap edges and seal with tape; secure against wind and avoid wrinkles that can puddle water.

Exposed aggregate process

Apply surface retarder after screeding; after concrete sets (4–24 hours), scrub with a brush and water to remove mortar and expose aggregate; keep aggregate size and color consistent.

Polished concrete grit sequence

Use progressively finer diamond abrasives (e.g., 30, 50, 100, 200, 400, 800, 1500 grit); apply densifier between passes and finish with a high-speed burnisher for gloss.

Acid stain neutralization

After applying acid stain to cured concrete, neutralize the acid with an ammonia solution, then rinse and allow to dry before applying a sealer.

Sealer types

Film-forming sealers (acrylic, polyurethane) form a surface coating and can be slippery when wet; penetrating sealers (silane, siloxane) soak in and are breathable; choose per exposure.

Epoxy crack injection

Inject epoxy into structural cracks wider than 0.3 mm to restore strength; clean crack with compressed air, seal surface, and inject under pressure until epoxy exits adjacent ports.

Spall repair procedure

Remove loose concrete to sound substrate, chip edges to 25 mm depth, clean, apply bonding agent, place repair material with similar thermal expansion, and cure properly.

Hydrodemolition pressure

Hydrodemolition uses high-pressure water (up to 300 MPa) to remove deteriorated concrete without damaging rebar; contain and treat runoff water.

Surface profile CSP

Abrasive blasting achieves a Concrete Surface Profile (CSP) typically CSP 3–6 for coatings; verify with replica tape and clean dust before applying repair material.