Breaking>Types of breaking materials

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Types of breaking materials


Materials that are brittle and whose strength comes mostly while they are in compression are the ones used in breaking, such things as cinder blocks, bricks, and ice. Other things, such as soft rocks and re-breakable plastic boards, may also be used. However, wood is the most widely used material for breaking.

Spring constant

Spring constant is a measure of the stiffness of a spring or a material. This constant is different between softer materials like wood and plastic and harder materials like brick and tile. If you were to look at a super slow-motion video of a material being broken, you will notice that the material does not break at the point of impact, it first flexes or “gives.” The more the material gives, the more "bounce" the material has. Softer materials, such as wood, have more give than harder materials, such as tiles.

If you punch a wood board, the energy stored in your punch is transferred into the board as it flexes. The board will flex until its tensile strength is exceeded and it breaks and carries away the energy. There will be a discomfort in the fist but not much pain. If the board does not break, the energy stored in the flex and is bounced back into the hand and arm. This causes pain in the hand but most of the energy is transferred through the locked wrist and dissipates into the arm.

If you punch a hard material such as a concrete block, it barely flexes before it breaks so it has negligible bounce. It either breaks or it does not break. If it breaks it carries away the energy of the punch and there is some discomfort to the fist but not much pain. If it does not break, most of the energy of the punch remains in the fist and the fist can be injured, causing great pain.

Elasticity of materials

As it relates to breaking, there are basically two types of breaking material: elastic and inelastic.
  • Elastic. Elastic material, such as wood, is pliable, which means it flexes and deforms when a force is applied and, when its tensile strength is exceeded, it splits apart and breaks on the opposite side of the one to which the force is applied. If the force is retracted before the material breaks, the deformation reverses and the material returns to its original shape. Some elastic materials have so much elasticity, that they are impossible to break using human strikes, such as plywood.
  • Inelastic. Inelastic material, such as a patio paver, is brittle, which means it does not flex or deform when a force is applied and, when it can no longer resist the force, it shatters. If the force is retracted before the material breaks, since the material did deform, it is still in its original shape. Some inelastic materials are impossible to break using human strikes, such as reinforced concrete.

Common breaking materials


Wood boards have poor consistency, even when they are obtained from the same tree. Even sections of board cut from a single log board can vary as to water content, grain structure, knots, cracks, insect damage, etc.  When you break wood a lot, sometimes you find a board that seemingly will not break.

Wood boards

White pine boards are usually used for breaking. The is soft and cheaper than other woods. Board sizes may vary but the usual sizes for breaking are 12x10x1 or 12x12x1. The boards can break at some point other than the impact point, so it does not have to be hit in the exact center when performing a break.

When choosing a wood board to break:
  • Choose softwood rather than hardwood. Softwoods, such as pine have wide grain, are less dense, and are relatively easy to break. Hardwoods, such as oak, have narrow grain, are very dense, and are practically impossible to break.
  • Choose boards with the least number of knots (wood will break around a knot, not through it). Avoid wood with knots that run along the length of the board. Small round knots are not a problem but avoid large knots, especially ones near the center of the board.
  • Choose boards that are the lightest in weight (less moisture content).
  • Choose boards that are the lightest in color (less sap content)
  • Choose boards that have grain lines that are the closest together. Since you are splitting the board along the grain, a board with the grain running in narrow bands along the length will be easier to break. The more grain that runs in a vertical direction, the harder the wood will be to break. 

Wood sticks, planks, or baseball bats

Long narrow boards, such as 2x4s or bats are always broken against the grain since the grain extends down the length of the board. You want to choose wood where the grain runs wide and flat.

Blocks or bricks

Blocks are made of cement with a small amount of aggregate (additional sand, rock chips, or pebbles mixed into the block to strengthen it) and are fairly consistent throughout. The smaller the aggregate the weaker the material. A concrete block made with no aggregate is fragile. Clay bricks also provide consistent qualities, but only when they come from the same batch and the same manufacturer.

Beware of reinforced blocks. They may look like regular blocks, but they are made with a stronger aggregate and/or contain reinforcing bars or mesh that makes them impossible to break. These blocks most often come in gray and red colors and can be flat on both sides, or the bottom may have small ridges. The color makes no difference, but ridges may make it very slightly stronger.

Blocks have a consistent hardness, but wet blocks are harder to break, so ensure the blocks that have been stored outside are dry. One block is equal to about five strong wood boards and is usually cheaper than one full-length board.


Rock breaking requires a very solid and reliable base, such as an anvil or head of a sledgehammer. Because of the molecular structure and complex irregular shapes of different rocks, rock breaking is unpredictable. Even extremely hard diamonds can be split along fault lines so choose rocks with fault lines that run in the direction of your intended break.

Choose a soft rock with no sharp angles on its surface. Rocks with a high moisture content break easier since the water acts as a lubricant between the sliding molecules of the rock.

When striking a rock, do not lay it on the base and start hitting it. The rock must be lifted slightly from the base, so there are two support points. Since rocks do not flex much, the lift only needs to be a small amount, never less than 1/4" or more than 1/2". The longer the rock, the more distance there will be between the support points. This gain in leverage will make it easier to break the rock. The surface of the rack at the impact point should be relatively smooth.

Strike the rock at a point equidistant between the two support points, usually using a knife-hand strike. You cannot hold back on the strike, so you should have a lot of experience with breaking before tackling a rock break.

Plastic boards

Plastic rebreakable boards are popular since they may be reused. The initial cost is high, but over time, the cost is recovered, and money is saved from not having to buy expensive wood boards. New boards will be difficult to break but after some wear, they break fairly consistently. However, after repeated use, their consistency of performance will quickly degrade, making them easier to break. This may give the practitioner a false sense of achievement, since they may think the board is easier to break because of their increased breaking skill. This may cause problems when changing to breaking more difficult breaking mediums. Some characteristics of plastic boards:
  • Plastic boards only break in one place, so they must be hit on the split line. 
  • Plastic interlocking "fingers" that create the board's resistance to breaking are susceptible to temperature. The warmer a board is, the easier it is to break. The colder a board is the more difficult it is to break. Breaking resistance decreases the more times a plastic board is broken.
  • Be careful when re-chambering the hand or foot after a break, the backward-facing fingers on the board may dig into the hand, arm, foot, or leg as it retracts and injure it.
  • The boards can easily be tampered with to make them easier to break.


Ice is consistent if it has the same temperature throughout, which is difficult to maintain. Cloudy ice indicates it has air bubbles in it and is easier to break.

Ice is always broken when held between two supports. The more distance there is between the points where the ice contacts the supports, the easier the ice is to break. The thinner the ice is, the easier it is to break. If the ice is too thin compared to its length, it may break under its own weight. So, choose just the right thickness and length and it will take little effort to break the ice.

Other materials

Other breaking materials include coconuts, bottles, sheets of glass, about anything breakable. Be careful when experimenting with other materials.

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