After the demolition of the old walk, and the excavation for the new brick walk were completed, the next phase of the project included accommodating a drainage pipe from a downspout of the house that needed to cross under the walk, preparing the soil subbase, and installing the aggregate base.
To recap from Phase 1 : The original old concrete walk was in a less than optimal location – it was very close to the house, which limited the privacy of the living room; the old walk also did not provide a welcoming main entry feature. In the new design, the new dry-laid (sand joints) paver walk was to be relocated and given a more prominent position in relation to the front door, and included a landing at the base of the porch steps, extending the welcoming area of the porch. Also, the choice of clay brick pavers would give a rich texture and warm color to the area.
In this article we mention that the finished surface of the new walk design included a drainage slope. Pavements of any type need to be sloped for drainage purposes which include, but are not limited to, directing drainage away from a foundation and other building structures. Typically, a minimum slope for a dry-laid (sand joints) paver project is 2%. Every project has its own unique site conditions and issues that should to be addressed ahead of time during the design phase of the project.
Site Issues: Dealing with a Drainage Pipe
The drainage pipe from a corner downspout had to be properly installed so the water could drain correctly. For this project, a 4” corrugated flexible solid drainage pipe connected to the end of the downspout was positioned completely under the base material of the walk, still allowing the pipe to drain properly. A channel was dug for laying the pipe, with enough space entirely around the pipe for a minimum of 2″ of coarse bedding stone. This bedding stone helps to keep the pipe positioned correctly after it is covered; it also helps prevent the pipe from becoming damaged from naturally occurring ground movement, including sifting caused by freeze-thaw cycles.
The pipe was installed with a positive slope that would ensure the water would flow and drain to its outlet. When installing a drainage pipe, keep in mind that the end of the pipe at its outlet has to be lower than the upstream end where the water enters the pipe, and all points along the length of the pipe, moving toward the outlet, have to decrease in elevation for proper drainage.
Preparing the Subbase
The subbase is another word for the ground just beneath the aggregate base. It may be hard to believe, but for engineering a strong and durable pavement, the condition of the subbase is very important. Without a strong and stable subbase, pavements of any type can structurally fail which results in cracking and/or settling.
To prepare the subbase, all soft soil areas needed to be replaced with a suitable soil type, and/or reconditioned with the addition of stone and aggregate.
The excavation is fairly rough at this point, and it will sort of resemble the shape of the finished walk. The excavated area was checked to make sure the depth was correct for the entire walk structure. This was done by running string lines connected to stakes across the excavation to take measurements for the required depth. The string lines were set at the height (elevation) of what would be the finished paver surface of the walk along with its correct slope (a line level attached to the string line, digital, or laser level helps for setting the correct slope). The measurement was taken by measuring from the soil of the subbase up to the string line (see schematic diagram). To adjust the area to the correct depth, add or remove soil as needed, and compact again. This measurement was taken several times during the process, and after compaction.
Calculate the depth required for your project by adding the layer thickness for each material used: The required depth for this project was 7 1/4” ( 4” aggregate base, 1” bedding sand, and 2 1/4” clay brick pavers installed in a basket weave pattern).
When this stage of work had been completed, the entire subbase had been properly compacted and sloped away from the foundation, and was ready for the installation of the aggregate base.
Installing the Aggregate Base
After the subbase was prepared, the 4” aggregate base was installed, which is the typical base thickness for walks and patios. The design plan’s finished width for the walk was a generous 4’-8″ width; a wider walk invited users to walk at a relaxed comfortable pace, in contrast to the narrow utilitarian feel of the old walk. Also, this width provided for an easier installation since no pavers needed to be cut.
The base was extended 6”on all edges beyond the finished width of the walk, except for where the walk was against another structure, such as the porch steps. This 6” extension of the aggregate base is for structural purposes to ensure the stability and integrity of the finished walk. Also, the extended base serves as a base for the installation of the paver edge restraint, installed in the next phase.
Graduated limestone aggregate was used for the base, which is a granular material with pieces ranging in size from 3/4” to granular fines (tiny pieces). This base material needs to be damp when compacted for proper adhesion of all the aggregate particles. When compacted, this type of material creates a very strong and durable base. This aggregate base is typically installed in 4” layers, or lifts, and then compacted with a vibrating compactor. It is important to compact the base material with the same percent of slope as that of the design plan’s finished slope, to ensure that water will surface drain in the intended direction once the project is finished.
If you are considering a dry-laid paver project as a DIY project, don’t think you can correct the slope or even wait until the end of the project to concern yourself with giving the pavement a slope for drainage – the correct slope of the pavement starts at the beginning of the project and is carried through as each layer of material is added. Adjusting the paver slope by adding more bedding sand on one side will not ensure a reliable slope – the slope needs to be an integral part of the structure to ensure permanent and proper drainage. Without good surface drainage, water may flow back toward your foundation, and may cause slippery conditions when wet. Also, pavements that stay wet, make great environments for mildew and algae to grow, which can create slippery walking surfaces, also.