Concrete may seem strong, but after many years, elements, and pressure, it will eventually crack. So in order to make your concrete last as long as your money that went into it, adding a layer of crushed stone under a slab of concrete will increase the life of your investment.
Here are 3 reasons why a layer of crushed stone is important to the life of your concrete:
A Level Surface
Adding crushed stone under your concrete slab will provide a level surface for your foundation. Simply pouring concrete onto the ground will expose it to elemental erosion that will cause cracking and sinking. Similarly, if there are roots or plants under your slab, they may rot and cause unevenness. Pouring concrete over crushed stone, however, will eliminate these worries.
Because concrete is a very porous material, it will absorb any moisture that it contacts. This can cause pooling. Without crushed stone, pooling water will settle under it and erode your slab. Adding a layer of crushed stone will add proper drainage, as well as create a barrier between your slab and the ground. For added protection, consider adding a vapor barrier as well.
Over a long enough time, concrete is prone to cracking. A flaw that can lead to unevenness. So while this is typically caused because of movement and shifting in the ground (due to poorly compacted soil, or soil type), a layer of crushed stone will greatly reduce the chances of this happening, and increase its longevity.