There are lots of different types of sub-bases for artificial lawns and it's important to make sure that the right sub-base is used for your artificial grass. The best type will vary depending on the use of your artificial turf, but the most important element is that the sub-base provides a non-expansive surface for your synthetic turf to be installed on.
What is a sub-base?
Sub-base is the term we use to describe the area that lies directly underneath the artificial grass. It is commonly made up of a sand/gravel mixture, although in some instances it could be concrete or asphalt if placing artificial grass over a patio, or even a wood base if installing over a deck.
A sub-base is used to replace the expansive native soil with a non-expansive surface. Native soil is very expansive and will expand and contract depending on the weather - wet soil expands and when it dries it will contract. If artificial grass is simply laid on top on native soil without a sub-base, the expansion and contraction can result in wrinkles and/or soft spots and can create an uneven surface for your artificial lawn over time. A good non-expansive sub-base is necessary for the artificial grass to continue to look good over it's 15-20 year life. Installing a synthetic lawn is a large investment, so it's important to make sure it's done properly.
Types of sub-bases
High Performance Bedding (HPB)
HPB is the base material of choice at Lazy Lawn for the installation of artificial grass for lawns. It consists of a 3/8” washed limestone chip and we'll even add 3/4 clear limestone rocks for added strength. It's the best sub-base for the installation of artificial turf for lawns because it compacts to approximately 97% providing a strong non-expansive surface, while maintaining a porous and drainable base. It's important to make sure the sub-base of your artificial lawn is highly drainable so rain water is able to go through it and into the native soil providing necessary ground water for the trees and shrubs in your yard. It also keeps rain water from overwhelming aging sewers.
Limestone screening is a crushed limestone product made up of chips (1/4”) mixed with dust. It is typical used as a grading base under patio materials. We'll use it only for building and grading putting greens that don't require drainage, but require enhanced strength. We do not recommend using this base under you artificial lawns, yet many competitors continue to use it. Limestone dust doesn't make a good sub-base for lawns because it creates a non-drainable surface. It compacts down and becomes concrete, which doesn't allow rain water to drain into the ground. Without ground water trees and other large shrubs won't survive. This type of sub-base will also cause rain water to run off the lawn and into the sewer system.
Crushed miscellaneous Base (CMB)
CMB typically comes from recycled concrete and/or recycled asphalt and consists of a sand/gravel mixture of 3/4” to fine. Class II road base is similar but is subject to more stringent testing, which makes it more expensive. This is the best type of sub-base for building sports fields. It can be used for other artificial turf applications, however it adds unnecessary cost to the project.