How to Lay a Concrete Floor Over a Gravel Basement

Rake the gravel floor smooth. Check it with a 4-foot level or a string level on a string stretched from one corner of the basement floor to the other. Once the gravel is smooth and level, tamp it down by going over it with a construction vibrator, a power tool that compacts the gravel and makes it more stable.

Snap a chalk line around the perimeter of the basement walls to indicate where the top of the finished concrete floor will be. Use a 4-foot level to make sure this line is level all around the perimeter.

Install rigid foam insulation if you are making an insulated floor. Tape the sheets of rigid foam together with construction tape. This material will double as a vapor barrier, keeping heat in and moisture out of your basement.

Install a layer of wire mesh over the surface of the rigid foam. This wire mesh helps strengthen the concrete and keeps it from cracking.

Feed the trough from a ready-mix concrete truck in through the basement window. It's possible to mix your own concrete, but for a job the size of a basement floor it isn't recommended. Extend the trough as close to the center of the floor as possible. As the wet concrete comes down the chute, catch it in wheelbarrows and push it to all corners of the basement. Having helpers for this job will be very helpful.

Flatten and compress the concrete by going over it with a steel-tined rake, jiggling the rake to work air bubbles out of the concrete and pushing the surface of the concrete around to make it even.

Flatten and smooth the surface of the concrete by working over it with a long 2-by-4 that you have checked for straightness. By moving the 2-by-4 back and forth in a sawing motion as you draw it across the surface of the concrete, you can create a smooth and flat surface.

Create an extremely smooth surface by employing a power trowel later in the curing process of the concrete. A power trowel is a large power tool that looks like a giant fan pointed at the floor. The blades of the fan spin against the surface of the concrete, creating a smooth, virtually blemish-free finish. You can't use the power trowel until the concrete has set up enough to walk on top of it.