Surface Preparation and Removal Techniques
Domain focus
This domain tests how to produce a sound, clean, rough, and properly conditioned concrete surface without damaging the substrate. Expect questions on ICRI CSP profiles, removal methods, edge geometry, and verification.
Core rules
- ICRI 310.2R uses Concrete Surface Profile (CSP) numbers 1 through 10. CSP rises with profile amplitude: CSP 2 is grinding, CSP 3 light shot blasting, CSP 5 medium shot blasting, CSP 7 heavy abrasive blasting, CSP 9 very heavy scarification, and CSP 10 a roughened surface.
- The surface must be sound, clean, rough, and saturated surface-dry (SSD) for cementitious repairs. Remove laitance, dust, oil, curing compounds, and loose material.
- Removal methods include hydrodemolition, abrasive blasting, scarification, grinding, milling, and chipping. Hydrodemolition removes deteriorated concrete selectively and avoids microcracking better than impact tools.
- Avoid featheredges. Saw-cut vertical edges to a minimum depth, typically about 6 mm (0.25 in), and square the repair boundary.
- Use light chipping hammers near remaining concrete to limit microcracking. Heavy impact can damage the substrate that must carry the repair.
- Verify soundness by hammer sounding and visual inspection after removal; re-prepare areas that are still unsound.
Worked example
A parking deck spall is 50 mm deep with adjacent microcracked concrete. Reasoning: hydrodemolish or lightly scarify to remove unsound concrete, saw-cut a square perimeter about 6 mm deep, then abrasive-blast to CSP 7 for a cementitious patch. Clean dust, saturate the substrate, and place at SSD with no standing water. Do not acid-etch a structural repair or feather the edges; both leave weak bond boundaries.
Traps
- Overpreparing and creating microcracks in sound concrete.
- Leaving dust or slurry on the surface after blasting.
- Feathering repair edges instead of square-cutting.
- Assuming a high CSP number guarantees cleanliness.