An essential part of an interlocking concrete pavement is a compacted aggregate base. No job should be installed without it. Some simple guidelines on selecting and installing a base follow. Following these guidelines not only will decrease the likelihood of settlement, but will produce a long-lasting paving job.

What is the base?

It is stone, generally ranging 3/4" in size to very small particles called fines. The best material to use is crushed stone. This kind of base is made from stone crushed at a quarry. It is graded or sorted after crushing by placing it on screens of different sizes. The sorted stones are mixed together in various proportions to create a range of particle sizes. The range creates a dense material when compacted. A high-density base allows for the best spreading of loads across the soil subgrade.

How do I know I have the right mix of particle sizes?

Crushed rock normally used under asphalt driveways and roads is generally acceptable under concrete pavers and bedding sand.

Where is the base placed?

It is placed over compacted soil subgrade. It rests under the bedding sand and pavers.

How is it sold?

Crushed aggregate base is sold from quarries by the ton, plus delivery. One ton will cover about 50-55 square feet when compacted to a 4" thickness.

How much base do I use?

That depends on the application. For patios & walks, a minimum of 4" to 6" should be used. Driveways will require a minimum of 6" to 8". Remember, these are minimums. Base thickness may need to be increased from 2" to 4" in soils that don't drain well, in those continuously wet from a high clay content, or in low-lying area. The minimum dimensions given here are compacted thicknesses.

How is it installed?

In "lifts" or compacted layers about 2" to 3" after compacting. Each lift is spread to a 3" to 4" thickness and compacted.

How can I tell when there is the right amount of moisture in the base to be compacted?
Here's a quick, simple test. When the base is spread in a lift, take a palm-sized sample from it and press it into a ball in your hand. Drop the ball about one foot onto a hard pavement surface. If the ball breaks into fairly consistent size chunks, then the moisture is about right. If the ball hits the pavement and particles of all sizes scatter in every direction, then more water should be added to the lift. Lightly spray (do not hose) water evenly over the spread base and test another sample using the ìdropî test. Excess water will cause the ball to not break into pieces. A bit of moisture will be left in your hands.

What about maintaining the slope or grade for drainage?

Slope the base away from buildings for drainage to remove rain and snow. Walks and driveways should also slope to remove water. Donít slope the base by decreasing itís thickness. Rather, create a slope by first grading the soil before placing the base.

A recommended minimum slope in the soil subgrade is a 1" drop for every 5 feet, or about 1 1/2%. The grade of the excavated area should reflect the slope and elevations of the surface of the pavement. Maintain a slope while keeping a consistent thickness throughout the base by using string lines tied to stakes. Set the lines to mark the final grade. Check the depth measurements along the string lines when excavating the soil, placing and compacting the base, as well as when setting and compacting the pavers.