How to Pack Down Rock Before Pouring Concrete

Concrete's strength comes from the compactness of its base.

A building is only as strong as its foundation, usually a concrete pad. Often a concrete foundation has a foundation of its own: the gravel base under the concrete. This base must be strong enough to support the weight of the concrete so that the new pad does not crack as it cures. Packing the rock under your concrete pad is essential to provide this strength. Most people will not own the tools needed to complete this project. Luckily, your local equipment rental store will have the tools you need. Once you have built your forms, it is time to make a gravel base.

Things You'll Need

• Shovel
• Gravel
• Rake
• Jumping-jack tamper
• Pad tamper
• Board (2 inches by 4 inches by 10 feet)
• 4-foot level
• Work gloves
• Safety glasses
• Hearing protection

Instructions

1. Don your work gloves and safety glasses. Shovel a 6-inch layer of gravel into the forms. Rake the gravel base flat. Take your time and be sure that the entire area is covered with an even layer of rock.

2. Lift the jumping-jack tamper over the form and place it onto the gravel. Start the jumping jack and tamp around the outer edges of the form. Be careful not to hit the form and knock it out of place. Remove the jumping jack from the work area.

3. Lift the pad tamper onto the pad. Don your hearing protection. Start the machine and tamp the remainder of the pad. Maneuver the tamper around the entire pad twice to ensure complete compaction. Remove it from the area.

4. Tamp the outer edges of the gravel pad with the jumping jack tamper two more times to complete the compaction. Remove the equipment from your work area and inspect the end result for waves or irregularities.

5. Lay the board on the gravel and place the level onto the wood. Check to be sure the bubble in the level is between the marks indicates a flat surface. Check several spots on the pad.

6. Add gravel to any low spots on the pad. Remove gravel from high spots with your rake and shovel. Re-tamp the entire pad twice with both machines, following the procedure described above. Check the gravel base's levelness again. Repeat as necessary until the base is perfectly level.

Tips & Warnings

• Work gloves and safety glasses are required when using hand tools.

• Hearing protection is required along with your gloves and glasses when using tampers.

• Never lift a tamper alone. The extreme weight of these machines requires a two-person lift to ensure the safety of the people involved and the integrity of the forms.

References

• Ask the Builder: Pouring Concrete Sidewalks
• Concrete-Catalog.com: Soil Compaction Handbook
• Reader's Digest: Crushed Stone Path