In 2017 I started hearing from our paving stone manufacturers about a “new” method of installing paving stones using clear gravel instead of the customary ¾” Minus road base we had been using since I started. We had already been using clear stone under our natural stone steps with great results so this installation method made sense for use under pavers as well.
Clear stone base had many benefits:
- It is much closer to final compaction as soon as it is dumped into the excavated area therefore requiring less compaction to consolidate the stone.
- It has greater frost heave protection due to the fact that there is no water being held in the base gravel (if installed correctly).
- Permeable interlock driveways or patios can be achieved by using a permeable jointing sand or gravel.
- Pavers are better protected from salt damage because salt is not being held in close proximity to the bottom of the stone.
There are also some considerations for using open graded stone base instead of a conventional base:
- Spiked plastic edging will not hold in clear stone. Modified wedge style aluminum edging or poured in place concrete edge must be used instead.
- Subsurface drainage is critical to this installation method. If you dig a hole in clay soil and fill it with clear gravel you will have a pond under your pavers which will negate any of the positives listed above.
- Separation fabric is a MUST between excavated base and clear stone backfill to prevent mixing and eventual settling.
- Conventional washed sand bedding layers should be separated by fabric or better yet switch to ¼” clear stone or High Performance Bedding (HPB) under pavers.
- Clear stone is slightly more expensive than conventional road base but we find the savings in compaction labour and higher quality longer lasting installs more than outweigh the difference.
The technology has been used for centuries in railway bed construction with great success under those extreme load conditions. We made the switch to open graded in 2019 for any project that had well draining subsoil or a sloped area we could shed water to. This really is the Achilles heal of this installation method if you don’t have the site conditions to allow for drainage it is better to use a conventional road base (Granular ‘A’ or ¾” >0”) to prevent problems.
One common myth I have heard is that clear gravel is 98% compacted as soon as you dump it in the hole and does not really need compacting. In our experience we still see a driveway base settle 1”-2” after compacting and consolidating. The angular gravel needs to be vibrated to find it’s “home” or to tightly pack the individual stones into the smallest space possible. For interlock driveways we use at least a 1000lb diesel plate compactor to achieve this desired state. For further protection we will install tri-axial drive-grid half way through the base profile to ensure long term stability and to prevent point loading from car tires rutting the interlock.
With over 3 years of projects installed using this method and ZERO call backs I can say that is has been a resounding success and we will continue to use this base preparation method on any new project where site conditions allow.
For more information on how we can help you create your dream interlock driveway or long lasting landscape project contact us to set up an in-home or virtual consultation today.