Using Crackit: Pre-drilling Holes

Good breaks start with the right holes. Use our hole design guide for initial diameter and spacing, then drill a few test holes at different settings if you're unsure. Compare how each one cracks and lock in your final pattern from there.

Drilling equipment and direction

1. Equipment: Electric drill, rock drill, or crawler rig — whatever suits the site.
2. Direction: Vertical holes are preferred. On walls or pillars where vertical isn't practical, angle the bore. Deeper holes generally give better results; on thin sections, an angled hole can reach useful depth. Horizontal spacing can match vertical spacing.
3. Diameter and spacing: Follow your design chart. In most jobs, 40–50 mm diameter works well.

Hole depth

1. Maximum depth: 10 ft (3.05 m)
2. Minimum depth: At least 4× the hole diameter — e.g. 5″ deep for a 1¼″ hole, 6″ for 1½″. Shallower holes risk blow-outs.
3. Recommended depth: In reinforced concrete, drill 90–95% of thickness. In ledge rock, drill to the depth you want removed. In boulders, go ⅔ to ¾ through. Soft rock (marble): 100% of height. Medium/hard rock (granite): about 105%.

Hole pattern tips

1. Always give the expanding mix a free face to push toward — e.g. a 45° hole on a flat ledge lifts upward; straight down may trap pressure.
2. To break a slab without pushing the surrounding walls, drill a cone pattern at the centre and fill those holes first — the core pops up and creates a free face.
3. Spacing depends on tensile strength, rebar content, and desired piece size. A starting point: 1 ft apart in rows, 1.5 ft between rows. Plain concrete can go up to 30 cm spacing.
4. Tighter spacing = faster breaks and smaller pieces, but more labour and powder.
5. Boulders break more easily than heavily reinforced concrete — holes can be farther apart when speed isn't critical.
6. Leave some holes empty to steer crack direction — cheaper than filling every bore, but slower.