Coming to Grips with Gravel: What it is and How it’s Used
I have a friend who has gotten herself into a tizzy about gravel. Really? As she sees it, gravel is everywhere – at home on the driveway and neighborhood roads, at work on walkways and by flowerbeds. It’s by culverts and drains, in parking lots and on roadsides.
Not only does she see it everywhere, she has noticed how once it is put down, it spreads, creeping into the grass, popping onto asphalt. After multiple applications, the result is a gravelly, rocky landscape.
I understand her comments. Gravel does create some issues; however, most of the time it is used instead of concrete or asphalt. Gravel is an inexpensive material that can slow down water and help with erosion. In my opinion it is a pain, but it is better aesthetically than concrete or asphalt, and it solves – not creates – drainage issues.
Long ago, before concrete and deforestation, erosion was controlled by vegetation on the ground – leaf and plant debris. Now, we have lots of impervious surfaces that funnel water and cause erosion problems. Also, every time a tree comes down, the ground surface is impacted. The roots help to hold the soil and stop erosion. Every new subdivision where trees are removed and topsoil is regraded and removed causes more and more erosion and water problems. What can no longer be handled by the forest has to be handled by some type of drainage, and gravel is part of the solution.
Art of Stone Gardening uses lots of gravel for both structural and drainage work and for decorative work. We use two types of gravel. The gray stone most often seen is made from granite quarried in Georgia (Local product!) It is the best for drainage, walkways, driveways and compaction.
The white/beige stone that we use is from rivers. It is smoother and does not compact well. We do not use this for drainage.
Understanding the Stuff
Gravel is sold by size, from fine powder to football size, and assigned a number. “The smallest is usually #10, #57 sits somewhere in the middle, and the biggest is usually #1. The number system is more often related to what the gravel is intended to be used for rather than its measurements.” (homequestionsanswered.com)
Granite 89 is a mix of 8 and 9 gravel stone. It is very small and is what is used for walkways. Granite 57 is a mix of size 5 and 7 stone and is used behind and below walls. Granite crush and run, or crusher run, is a combination of pulverized stone with granite dust. The stone dust mixed with the crushed stone allows for very little air between the material making it valuable for its compaction ability and use in construction and driveways.
Keeping It Under Control
The best way to contain gravel from creeping and spreading is with a metal edge, which works best for walkways and other low impact areas.
Containing gravel on a driveway is more difficult. The problem with metal edging for driveways is that the ground is often not level. The edging is only 4” deep and roots and slope make effective installation difficult to get a uniform depth. Eventually, the edging sags, comes up in places when tree roots move, gets pushed out with cars compacting the gravel, etc.
An alternative for driveways is to use large stones along the edge to contain the gravel, but this is expensive and labor intensive. Especially with long driveways, lots of stones and lots of labor to dig out the edge = lots of $$. Concrete is best for driveways, but it is also expensive.
Structurally, gravel is used under and behind walls for drainage and to relieve hydrostatic pressure. Hydrostatic pressure is “the pressure that a fluid exerts against a solid surface due to the existence of gravity. Gravity forces the fluid in a downward direction, causing it to sit flush against a wall, a floor, or, in the case of basements, a foundation.” (ArmoredBasement.com)