Granular M or ⅝” minus is the product of choice for driveways, laneways and parking areas and our best seller. It has the right blend of crushed fines with a coarse aggregate that compacts and binds together. Granular A can also be used but is recommended for higher-traffic municipal roads. Granular A is a ⅞” minus product with larger particles that have a tendency to roll to the surface and do not mesh and pack as well as the finer Granular M. This results in issues with snow blowing and snow ploughing and is less desirable to walk on.
Paving Stones are a manufactured concrete product and therefore have a very accurate thickness tolerance, allowing for the base layer to be accurately levelled and compacted. Therefore, Granite Screenings are easy to ‘screed’ into a smooth compacted layer and are recommended as the under layer for paving stones.
We find all landscapers have their own preferred products and methods. The following is the rationale we use as we are asked this question a lot. On our projects, we typically use ½” clear below a flagstone patio, we do this for a few reasons: 1.) Clear stone does not require compaction and cut flagstone is not always a perfect thickness, and therefore, it normally requires some minor adjustments to the granular layer. Levelling with screenings or Granular M means if the top material is loose, it could compact and result in minor settling. Using clear stone, we find we can set the flagstone with less risk of future settling. 2.) the clear stone offers a drainage layer. 3.) ½” clear is easier to grade and work with than a larger diameter stone below a patio. However, for stair treads, a larger diameter stone is recommended depending on conditions. Drainage is a very important aspect of setting stair treads. If the area is susceptible to water, use larger stone, it will allow for water to flow. We have seen stair treads wash out because of a too-small drainage stone used.
If you have high water flow on a slope in a ditch line or drainage swale, you can choose a round stone (river rock) or a crushed granite product. Product size is subjective and based on the volume of water and the steepness of the slope you are dealing with. For a lower degree of slope or lower volume of water, you can choose a smaller River Rock (1-3”) or smaller 2” clear crushed granite. For a higher degree of slope or higher volume of intermittent water, you can choose larger River Rock (4-6”) or larger 4” or 6” clear stone crushed granite.