Specialty Finishes and Surface Treatments
Specialty finishes and surface treatments covers decorative and functional surfaces (stamped, exposed aggregate, broomed, dry-shake hardened, polished, sealed and coated) and the preparation each one demands.
Core rules
- Exposed aggregate: place, bull float, then spray a surface retarder at the product rate; wash with a fine mist and soft brush when the cement paste has softened but the aggregate is locked. Test a panel first.
- Stamped concrete: integral or surface colour, then a release agent, then mats pressed when the concrete is stiff enough to hold an impression. Stamping does not replace joints; cut them.
- Dry-shake hardeners are broadcast at the specified rate, usually in two applications, on plastic concrete free of bleed water, then power floated in.
- Broom finish: drag a stiff brush transverse to the slope, at the point where the surface holds the texture without tearing.
- Polished concrete: a sequenced diamond grind from coarse to fine, densifier, then a guard. Test moisture before any coating, using in-situ relative-humidity probes or the specified method.
- Surface preparation follows ICRI concrete surface profiles: coatings typically need CSP 3 to 5, overlays CSP 6 and rougher. Shot blasting, grinding or scarifying, not acid etching.
- Sealers are film-forming or penetrating; check slip resistance and reapplication intervals.
Worked example
A 250 square metre slab needs a dry-shake hardener at 4 kg per square metre. Total is 250 times 4, which is 1,000 kg. In 22.7 kg bags, that is 44.05, so order 45 bags. Split it: broadcast about two-thirds, roughly 30 bags, while the concrete is still plastic, float it in, then broadcast the remaining 15 bags at right angles and float again. Applying all of it at once produces laps, dark patches and hardener that cannot be worked in.
Traps
Stamping too early, when the concrete will not hold the pattern, or too late, when it needs excessive pressure. Washing exposed aggregate too late, tearing the surface, or too early, leaving paste. Sealing damp concrete, causing blushing and peeling. Skipping a trial panel on a decorative mix.