Are you going to be installing any type of pavement in your yard, such as a paver driveway, patio, or walk? Even if you will be hiring a contractor to install concrete or asphalt, or a skilled mason for a mortared pavement, you’ll find it beneficial to have an understanding of the importance of a good sound gravel base for any hard surface.
The pavement you see in various areas of your yard is really the finished surface, and not the pavement’s entire structure, much like the hardwood flooring in your house. There’s a whole structural system at work under the hardwood planks that actually create the floor of a room.
Pavers, asphalt, slate, or whatever hard surface materials you chose for your outdoors are the finished surface. For a long lasting pavement, there needs to be a strong underlying structural base. The quality of this base is vital to the success or failure of an outdoor pavement project. If properly constructed, the gravel base along with a well prepared subbase (ground below gravel base) can provide you with a stable and durable foundation for your pavement for years to come.
A non-structurally sound gravel base and subbase, and a gravel base that is not the correct thickness for the weight that it will bear, can make your pavement vulnerable to damage from forces above and beneath the pavement. Forces from the movement of the underlying ground can cause damages that include raised or sunken pavement, pavement and mortar cracking, paver and stone shifting. Damage can also occur in the form of depressed areas or compaction from greater load-bearing weights that the gravel base was not designed for.
Established methods in the construction industry have set building standards for all types of construction projects. Constructing the gravel base for a pavement is no exception. The materials for the base are typically made up of a 100% crushed aggregate mix ranging in size of around 1” pieces to granular-size pieces (also known as fines). The base material should be free of any debris and organic material.
The quality of the subbase, beneath the gravel base, is important for a long lasting pavement, too. For a new project, after the excavation is complete, the subbase should be compacted with a heavy vibrating compactor, or a hand tamper. Any soft soil areas of the subbase should be removed and then filled with aggregate placed in 3” to 4” layers (also called lifts), compacting the aggregate after each layer. The subbase and gravel base should extend a minimum of 6″ beyond the finished edge of the pavement, on all sides that are not up against another structure.
If your project is replacing only the finished surface of an existing pavement, and not the gravel base, the gravel base should be inspected for areas that may need to have more crushed aggregate mix added to it, followed by compaction, to make it structurally stable.
The gravel base material should be placed in layers (lifts) and then compacted with the heavy vibrating compactor, or a hand tamper. The thickness of the base will depend on the type of finished surface material you chose (concrete, pavers, mortared slate, and so on), and the load-bearing requirements of the project’s intended activity. For example, an asphalt driveway will require 8” to 10” thickness of gravel base because of the flexible nature of asphalt, and the weight of the vehicles moving across, and parking on, the driveway.
Use the recommended gravel base thickness of the manufacturer’s product you are using, or the building supplier where you bought your paving materials. Your local building department can be a source for this information, also.