Natural stone paver driveways are a thing of beauty, a real estate highlight, and a feat of engineering. They increase property values, up the curb appeal, and boost resale prices. So, what’s the best way to protect that investment and maintain its physical appeal? Let’s start at the basics, which means ensuring the natural stone driveway installation is done correctly.
There are two options for natural stone paver driveway installation.
And, at Gothicstone, we suggest all ‘dry set’ and ‘wet set’ installations include a cellular confinement system (CCS) underneath for maximum longevity and lifetime value.
An issue with ‘wet set’ (poured concrete slab substrate) particularly in climates that have a lot of freeze-thaw cycling, is that concrete slabs are used as the sub-base/substrate and often will crack. It’s often not a question of “if” the underlying concrete slab will crack, it’s “when” it will crack. And a cracked concrete slab will commonly transfer the crack(s) to the adhered surface stone or any material on top, such as concrete pavers, for that matter. The reality is very few contractors are willing to put the effort into making a slab that won’t crack because it takes extra work and expense. Utilizing rebar, a geo cellular confinement system, and a ‘separation membrane’ (such as Schluter®-DITRA & DITRA-XL) will mitigate the possibility of failure, as described below.
Some people think the cellular confinement system isn’t needed under a large concrete slab. But we disagree. The fact is the minimal extra expense will all but guarantee that you will never have slab cracking. Water is going to get underneath the concrete slab and during freezing, it will expand. The cellular confinement system holds everything in place minimizing movement resulting from freezing and thawing environments.
To recap, if you want your installation to last a long time, follow these 9 steps:
In conclusion, there are redundancies in the above best practices instructions. There is almost zero chance of failure if all these steps are completed, and the resulting driveway should last a lifetime.
‘Dry set’ installation is the ideal method for driveway stone pavers. It avoids excessive movement of the stone due to heaving in colder climates. Also, stress from an expansion of the stone in hot climates. These unwanted issues are inherent in poured concrete slab systems. ‘Dry set’ installation is an environmentally sustainable alternative that allows water to pass through it rather than create problematic water runoff.
For the safest approach, it’s best to select natural stone pavers of smaller sizes. When working with smaller pieces, such as 4”x4”, 4”x6”, or even 6”x6” cobblestones, use a ‘dry set’ application. But if your customer wants something different than the classic cobblestone 4”x4” granite, limestone, or porphyry block, the key is to consider the flexural stress on the stone. If the stone surface is longer than 6 inches in any one direction, then a strong (high ‘flexural strength’) material is optimal, particularly when considering a ‘dry set’ application. Avoid natural stones prone to having natural fissures or clefting.
Large format pavers can be successfully installed if the installation is done properly. You can install 12”x12”x1¼”, 16”x16”x1¼”, 8”x16”x1¼” or larger if it is installed correctly. But that’s a BIG “if”. Many contractors/masons rely too heavily on laborers to do the installations, emphasizing speed over quality. This isn’t a good idea. A small void or a “pea under the mattress” can cause failure.
To mitigate shifting and cracking, install a cellular confinement system. Gothicstone recommends a cellular confinement system (CCS) under any base. With driveways, it’s almost imperative due to tire track “rutting” to use a CCS. For example, if you have a sand or dirt driveway, ruts inevitably occur over time. But it also happens with blacktop driveways or any driveway where you have constant stress and load on two narrow tire tracks. The vehicle load will compress the ‘track’ area, whereas a CCS can keep the substrate from spreading out. This method prevents stress on the tracks from making ruts in your installation, and thus pieces from failing. Because when the ruts happen, there’s uneven compression on the pieces. It’s the unevenness of the load where problems like this occur.
Small 4”x4”x4” cubes/pavers typically won’t break, which is why people typically use this size of material, but they will be susceptible to rutting and shifting. Often people want to use a larger format driveway stone. If so, a ‘dry set’ and a cellular confinement system are the approaches to use.
The larger pieces will help in that they won’t rut as readily, however, they may crack. Whereas small driveway stone pieces will allow the material to “sink down” into the ruts without breaking. But they’ll allow the ruts to occur more easily. Plus, more water is washing in between the joint areas because you have more joint areas.
If you have a 4”x4” compared to a 16”x16”, you’re going to have about 1000% more joint area with a 4”x4” installation. That’s an incredibly exponential amount of joint area because in a 16”x16” area, you will have 16 pieces of 4”x4” material (4 in one direction and 4 in the other direction) and then all those joint lines in between where the water will be entering and then allowing for either washout or heaving underneath it.
So, the smaller driveway stone pavers do allow for more movement to happen but, eventually, they may cause ruts unless you use a cellular confinement system to keep everything underneath in place.
Keep in mind that vehicular weight will be on the pathway of the vehicle tires; that is where the bulk of the load or stress will go.
To recap, if you want your installation to last a long time, follow these 8 steps:
Have questions on cellular confinement systems and selecting/specifying natural stone for driveway systems? Contact us.
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