Building a brick floor or patio over dirt is not as simple as flattening the ground and laying down bricks. If the ground under the bricks is not properly prepared, the bricks will quickly move out of place, succumbing to erosion as the ground beneath them wears away. With the right steps, however, a brick floor over dirt can last for decades.
Mark out the area for your brick floor. Trace it with a hose or string to outline the shape. Drive wooden stakes vertically into the ground along the border to mark out exactly where you will need to dig. Ideally, the stakes should go about 18 to 20 inches into the ground and be spaced every 2 to 3 feet.
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Dig out 8 to 10 inches of ground, leaving a level surface with a very slight slope. According to Easy2diy.com, your patio should slope 1 inch every 4 to 8 feet to let it drain.
Remove the stakes and line the hole with landscape fabric. Use the widest, thickest fabric available and completely line the bottom and sides of the hole, leaving 6 inches extra at the sides.
Pack 4 to 6 inches of gravel into the hole and tamp it down with a gas-powered plate tamper so that it is level. According to Reader's Digest, you can buy gravel either by the cubic yard or the ton. "One cubic yard... covers about 50 sq. ft. at a 6-in. depth by the time it's compacted, and weighs 1-1/2 tons."
Lay down 1 to 1.5" of stone dust or sand and tamp it down. According to Reader's Digest, you will need about 5 tons of sand for every 12 tons of gravel you use, including sand to put between bricks.
Lay the bricks down over the sand and tamp each one down with a rubber mallet to avoid scarring it with a regular one. Make sure that your bricks set level.
Spread a layer of sand or stone dust on the bricks and sweep it over your stone floor to fill in the cracks between the bricks. If you are using stone dust, water it to cause it to harden and hold the bricks more firmly in place.
Bend the edges of the landscape fabric towards the stone floor and bury them under dirt at the edges of the stone patio to secure them.