Stone Dust/Aggregate

 

 

 

 

 

 

 

 

 

 

 

Stone dust is a fairly common and inexpensive paving material which consists of small rock fragments, which may be open-graded or dense-graded depending on the product. Its color and consistency will vary, depending on the original source stone. It can be applied either in a loose, lightly compacted form, or with a stabilizer additive to help lock it in place. Its common applications include informal garden pathways, sitting areas, and other low use-intensity spaces. Stone dust products can also be designed specifically to be used as an interstitial aggregate between other modular pavement types, such as concrete unit pavers.

 

As a loose material, the surface of stone dust or aggregate pavement can be manipulated and sculpted to create stunning expressive effects in the landscape.

 

 

 

 

 

 

 

 

PROS & CONS

Advantages:

• Ideal for low-impact design areas, such as nature preserves or in community gardens, etc. Very low environmental impact of installation, and in many cases can be done with manual labor.
• Stone dust can be installed to fit just about any shape, can be very effective in irregular or curved layouts
• Can look attractive as a finish surface; depending on the source stone, its neutral colors can work well in a variety of landscape settings
• Cost-effective to install, with greater economy of scale the larger the area to be covered
• Tactile material, can add elements of  sound and texture underfoot

 

Disadvantages:

• Depending on the layout, it can be difficult to create a defined “edge” without a curb or other edge restraint to constrain it, and even then the loose aggregate may travel.
• Economical material, can look “cheap” next to premium building materials such as stone or brick
• In high-traffic areas, can be compacted to become impermeable, which may result in ponding or other surface water issues.
• Not suitable for sloped sites; at slopes greater than 1-1.5%, stone dust has been observed to wash out due to erosion by surface water runoff, even with the addition of a chemical stabilizer
• A combination of one or several of the above factors may result in considerable maintenance

 

 

 

 

 

 

 

 

CONSTRUCTION

The sequence of construction is usually as follows:

EXCAVATION/GRADING

As a first step, the area to receive stone dust will be excavated to allow for the desired depth of material to be placed. Depending on the pathway’s expected level of use, the depth and bearing capacity of the base material will vary. Once the excavation is completed to attain the necessary depth, the exposed earth surface below is compacted, usually to a minimum of 95% Proctor Density, or an engineer’s recommendations (because of the ways in which stone dust is typically used in the landscape, it is uncommon to have engineers weigh in on matters regarding stone dust pavement).

Once the subgrade is prepared, you may wish to add a weed barrier or other impervious membrane to prevent the colonization of weeds and undesirable plant growth through the loose aggregate profile. Such material is optional, but is commonly recommended by professionals. At this point, edge restraint products are also commonly installed, to complete the container into which the stone dust will be added.

AGGREGATE BASE

Depending on the expected level of use/traffic of the paved surface, it may be a good idea to add further aggregate base below the finer stone dust at the surface, to stabilize the profile and allow water to drain freely. This base aggregate should be distributed over the compacted subgrade in the area to be paved, and then lightly compacted, either by a vibrating plate compactor or a hand tamper (for smaller areas).

Once the base course is in place, the stone dust itself is added.

INSTALL STONE DUST

Stone dust will typically be installed as a single application, either placed by hand or with small machinery (for larger projects). It will then be rolled/lightly compacted, either manually or with small equipment, to pack it neatly into place. The thickness may vary from just a few inches to 4-6”, depending on subgrade conditions and whether a weed barrier is installed or not; generally, the thicker the application, the more initial weed suppression will be achieved.

For applications where stone dust is installed as an intermediate material between other modular pavement types, the primary pavement type will typically be installed first; once this is complete, the stone dust can be added on top and swept into the joints using a broom or hand brush. Once the material has been properly directed into the joints, it is often helpful to clean up by lightly watering the surface to wash any remaining stone dust into the open joints.

 

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