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There is no single base preparation method for pavers that will apply to every project. Instead, choosing the right base to install depends on variables that need to be considered on every project. Educating yourself on each of the methods to install pavers will provide you with a toolkit to provide your clients with the best possible end product while helping you stand out from your competition by doing so.
Gravel Bases for Pavers
Various aggregates have been relied upon throughout many years to construct a suitable base for pavement structures. In the hardscape industry, there are four such base preparation methods that have a wide range of aggregates, products, applications, and installation specifications. We use each one of these methods in our business for various applications. There is no base that is best for every application. We use the base that is most suitable for the application to provide our clients the highest quality end product that will stand the test of time. It is important to understand each of these base preparation methods and to choose the one that is most suitable for the project.
Base Material for Pavers
There are four different base preparation methods that will be noted in this article. These include the five different base materials for pavers listed below. You will note that stone dust or limestone screenings is not on this list. This material should never be used in a paver installation because of the multiple drawbacks that come with using this material.
Granular A, 3/4″ angular crushed down to fines, 3/4 minus
Concrete Sand, ASTM C33
3/4″ angular crushed clear stone, ASTM #57
High Performance Bedding, 1/4″ angular crushed clear stone, 3/8″ angular crushed clear stone, ASTM #8 or #9
Paver Base Panels, Synthetic Base, Geosynthetic Base
- Front Walkways on grade where the driveway has been completed using the same material.
- Some Retaining Walls.
A traditional base consists of a 3/4″ angular crushed stone down to fines also called Granular A or 3/4 minus. The bedding layer of this is a screed layer of concrete sand. This is the base that is recommended by ICPI in paver installation. The Granular A material is installed and compacted while adding water if necessary to help in the compaction of the material. The concrete sand is then screeded at no more than 1″ in depth for the pavers to be laid on top. During the final compaction of the pavers, the concrete sand will lift into the joints of the pavers creating interlock of those pavers. The 3/4″ angular crushed stone in the Granular A provides the structural integrity while the fines bind the base material together with compaction filling all of the voids.
However, in our business we do not use concrete sand our installations (with the exception of concrete overlays). We find that HPB or 1/4″ angular crushed clear stone is easier to work with in a traditional, open graded, or synthetic base. We are also able to use this material in the rain. For this reason, we mostly opt for an open graded base in our business for most paver installations.
Open Graded Base
- Raised Patios
- Some Retaining Walls
An open graded base is installed the same way as a traditional base, but with a different base material. This consists of a 3/4″ angular crushed clear stone also referred to as ASTM #57. This is accompanied by a separation fabric, either a woven or non woven geotextile, to separate the base material from the subgrade (also recommended in a traditional base). In addition to this fabric is a drainage system using perforated pipe to exfiltrate the water out of the system. High Performance Bedding (HPB) or a 1/4″ or 3/8″ angular crushed clean chip must be used as the bedding layer for an open graded base at approximately 1″. Concrete sand cannot be used in this application as a bedding layer as it will migrate into the base material.
The benefit of an open graded base is that the void spaces allow for the drainage of water that enters the system with little resistance compared to the fines in a traditional base holding that water for a longer time. This is a benefit especially in areas that experience freeze-thaw cycles. With no fines, there is no washout experienced which is also important in an open graded base where if there is any movement in the retaining wall or the gaps were slightly spaced the washout of fines would occur. It is also more difficult for weeds to take root or insects to make a home. Additionally, with rain not being a problem with the installation of this material, this will speed up efficiency as you will be able to take advantage of rain days where you could not with a traditional base. The base material has a higher compaction rate prior to mechanical compaction than a traditional base, making more efficient use of the aggregate ordered and requiring less effort to compact in relation.
Open graded base holds many benefits over a traditional base, but ultimately if the project is on grade we will opt for a synthetic base.
- Any pedestrian traffic project that is on grade and not tying into another pavement.
A synthetic base requires less than half of the excavation required in a traditional and open graded base. The benefit of this is obvious. Labor and disposal savings offset the cost of the paver base panels, and then some. This added savings along with being able to move onto the next job faster to fit more projects into your schedule in a season is the major benefit to this base preparation method. This is only applicable to projects that can be built on the existing grade and will only hold pedestrian traffic (though there is a vehicular traffic product on the market that I have personally yet to use).
This method requires a non woven geotextile to separate the subgrade from the base material which is just a 1″ bedding layer that is screeded using a concrete sand or High Performance Bedding / 1/4″ angular crushed clean stone. We always opt for the HPB rather than the concrete sand because of its higher rate of compaction without mechanical compaction. Additionally, concrete sand needs to be compacted prior to installing the paver base panels. This becomes problematic as after mechanical compaction, you would be required to level out areas with impressions from the mechanical compaction. With HPB, we would screed, lay our paver base panels, and move on to laying our pavers without mechanical compaction until we install the jointing compound and need to consolidate that into the joints.
Concrete Base for Pavers
- Where existing concrete has already been installed, is in good condition, and we feel confident enough in its integrity to build on top of it. Example: Pool patios and front porches.
The only application we would opt for a concrete base for our paver installations is when it is already present prior to pricing a project, it is in good shape, and we our confident in the structural integrity of the concrete. This is a lot of ifs and comes down to inspecting the area to ensure there are no cracks from signs of movement, as well as no significant variation through the surface area of the concrete. The only time we overlay concrete is for front porches or a swimming pool patio. These are the primary times that we would opt to overlay the concrete with pavers and other product if we are confident in it.