Decomposed granite (DG) is a natural, granular material widely used in landscaping. It forms from the weathering and erosion of solid granite, an igneous rock rich in minerals like quartz, feldspar, and mica. This breakdown results in a mixture of fine, sand-like particles and small aggregate fragments, typically no larger than three-eighths of an inch. DG boasts a natural, earthy aesthetic, with colors ranging from buff and gold to gray and deep red. When properly installed, it compacts to create a firm, yet permeable surface that blends seamlessly into the outdoor environment.
Understanding Decomposed Granite Types
The use of decomposed granite depends on its specific composition, which determines its stability and drainage properties. The most basic form is natural or loose DG, which contains no added binders and is the least expensive option. This material compacts over time but remains loose on the surface, making it excellent for decorative groundcover in garden beds. Loose DG is best suited for low-traffic areas where excellent water drainage is the primary concern.
A significant upgrade in stability is achieved with stabilized DG, which is premixed with a polymer or organic binding agent. This stabilizer cures when watered and compacted, locking the particles together to form a semi-rigid surface. Stabilized material minimizes dust, prevents erosion, and is necessary for surfaces that experience regular foot traffic.
A third type, resin-coated DG, is the most durable, utilizing a resin additive to create a surface similar to asphalt in firmness. This option costs more and is reserved for heavy-use applications like driveways, as it provides a permanent, highly stable surface. Screened DG refers to material processed to remove the finest particles, leaving a coarser aggregate that drains exceptionally well but does not compact as tightly.
Ideal Applications for Decomposed Granite
Decomposed granite is used in numerous landscape designs. One of its most popular applications is for creating patios and walkways, where a stabilized formulation is preferred. The binder creates a surface that is firm underfoot, preventing the material from shifting or tracking into adjacent areas.
For vehicular use, such as driveways, only a highly stabilized or resin-coated product should be considered to withstand the weight and turning forces of cars. The material’s permeability is a significant advantage, allowing rainwater to soak into the ground and reducing surface runoff. DG is also highly valued in xeriscaping, functioning effectively as a decorative, permeable ground layer in drought-tolerant designs.
Loose DG can also be used as an attractive, inorganic mulch layer around trees and planting beds. This layer helps suppress weed growth and retains soil moisture while slowly releasing beneficial trace minerals.
Step-by-Step Installation Guide
Proper preparation of the sub-grade is the first step for a durable DG installation, especially for high-traffic surfaces. Begin by excavating the area to a depth of four to six inches below the intended finished grade to allow for the base and the DG layer. The excavated area must then be graded to ensure a slight slope, ideally a two percent minimum, to facilitate positive surface drainage away from structures. After shaping, the native soil should be thoroughly compacted using a plate compactor to provide a solid foundation.
Next, edging must be installed around the perimeter of the excavated area to contain the material and prevent lateral migration. Common choices include steel edging, pressure-treated wood, or stone borders, which should be securely staked.
Sub-Base Installation
For pathways and patios, especially in areas with poor drainage or heavy loads, a sub-base layer of crushed gravel or road base is highly recommended. This base should be spread in two-to-three-inch lifts, lightly dampened, and compacted to create a stable, well-draining platform.
DG Layer Application
The DG material is then spread evenly over the compacted base, aiming for a finished depth of three to four inches. If using stabilized DG, the material should be spread in two separate lifts of no more than two inches each to ensure uniform compaction. After spreading the first lift, the surface should be lightly wetted, but not saturated, before compaction with a plate compactor. Over-saturation is a common error that can cause finer particles to rise to the surface, resulting in a slick finish that hinders permeability.
The final lift is then spread, lightly dampened, and compacted. For stabilized DG, the proper amount of moisture activates the polymer or organic binder, which cures to lock the particles together. Wait the manufacturer’s recommended time, often 24 to 72 hours, before placing the surface under heavy use to allow the binder to fully cure.
Maintaining and Repairing DG Surfaces
Maintaining decomposed granite surfaces requires occasional attention. Weed control is a continuous process since organic debris can settle on the surface and provide a medium for seeds to germinate. Applying a granular pre-emergent herbicide in early spring and fall significantly reduces weed growth.
Small weeds that appear should be manually pulled or treated with a non-toxic spot killer before they establish deep root systems. Over time, heavy rain or concentrated traffic can cause minor ruts, depressions, or low spots to form. Repairing these areas involves loosening the surrounding DG with a stiff rake, adding fresh material, and lightly re-compacting the area.
Loose DG surfaces may experience dust issues and gradual material loss due to wind and erosion. The surface can be lightly re-wetted or a topical stabilizer can be applied to re-bind the fines and reduce dust. Periodically adding a thin layer of new DG, about a half-inch every few years, helps replenish the fines and maintain the original finished level.