Using Crackamite: Pre-drilling Holes

Crackamite's effectiveness depends on the placement, diameter and depth of the holes drilled in the material. To determine the right combination of hole size and spacing, first make a reference hole design using the parameters from the hole design sections, then drill several holes of different diameter at different burden and spacing. Now check the break conditions of each of them and then decide hole diameter, depth, burden and spacing.

Drilling

  1. Drilling machine: Use electrical drill, rock drill or crawler drill.
  2. Drilling direction: It is preferable to drill holes vertically, but in case of a wall or pillar of reinforced concrete where vertical drilling is difficult, an inclined hole may be drilled. Since a greater effect is achieved with a deeper hole, in case of a thin material, consideration should be given so as to get a long hole depth by drilling it obliquely, if necessary. Horizontal holes can have the same spacing as with vertical holes.
  3. Hole diameter and hole spacing: The breaking plan of the hole design sections should serve as a guideline in making this decision. In general, the preferable hole diameter is from 40 to 50 mm.

Hole Depth

  1. Maximum Hole Depth is 10 feet. (3.05 meter)
  2. Minimum Hole Depth is 4 times hole diameter; for example 5" with 1¼" hole, 6" with 1½". Holes shallower than 4 times diameter are likely to blow out.
  3. Recommended Hole Depth: In reinforced concrete, drill 90% to 95% of its depth. In a ledge, drill as deep as you want to remove. In boulders, drill 2/3rd to 3/4th of the rock's thickness. In soft rock, like Marble, hole depth is 100%. In middle or high hardness rock, like granite, hole depth is 105%.

Hole Pattern

  1. Holes must be drilled so as to allow a free face for the Crackamite to push towards. For example, drilling at a 45° angle in the flat surface of a ledge will push it upwards, but drilling straight down might not allow the pressure to go anywhere.
  2. To demolish a slab without pushing out the walls, which surround it, drill a cone shaped pattern at the centre and fill these holes first. The cone will pop upwards and create a free face.
  3. Hole pattern depends on tensile strength of what is being broken, amount of rebar, if any, and the size of the pieces you want when you're done. This can often be determined by experiment; a good starting point is to space holes one foot apart, in rows, one and a half feet apart. In non-reinforced concrete, holes may be spaced as far apart as 30 cm.
  4. Hole pattern also depends on how fast you need results. More holes spaced closer together will give faster cracking time and smaller pieces, but will cost more in terms of labour and Crackamite.
  5. Boulders are much easier to break than reinforced concrete or ledge, and drill holes can be spaced further apart, especially if breaking speed is not critical.
  6. Empty holes can also be used to direct cracks - they cost less than filled holes. This will save money compared to filling all the holes, but will slow down the breaking time.
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