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Ensuring you are digging to the right depth while holding a consistent slope for your paving project requires an understanding of how to set up a string line and using a line level to set that up on the outset. This requires you to simply have spikes, string line, and a line level. Having just these three items is going to help you visualize that slope and to set up your project for long term success. Though it never hurts to have a rotary laser level handy for efficiency purposes. However, not everyone has access to one of these more expensive tool, but a string line is a great place to start.
Leveling Ground for Pavers
When you are first starting your project, you will need to map out the excavation area on a horizontal plane, but also have a tool to measure the depth of your project while you excavate to ensure a consistent depth or slope. For our paver project, we want the bottom of our excavation area to mirror the top slope of our pavement. In order to accomplish this, we need to set a benchmark that we can always measure from to ensure we have dug to the depth that we require.
This can be difficult if the benchmark is in just one area. It is also difficult when we consider the slope that we need to apply to our project. This is where the use of a string line and line level comes into play. These tools provide us with an inexpensive way to measure and apply our slope to the project and create a benchmark that we can measure from to ensure we are excavating to the depth that we require.
How to Use a String Line
The first step in using a string line for our paver project is to put a stake in the corners of our project. These can be simply wooden stakes or metal spikes that can be hammered and stabilized into the ground. We use a metal spike because we also use a collar that tightens to that circular spike that allows the string line to tighten around it easily and to move up and down as needed.
When choosing where to place these spikes, we need to consider that the excavated area of our project should extend past the final pavement surface by the depth of the base. That means if our base is 6″ in depth (the minimum), then our base preparation needs to extend past our final paver by 6″. It is at that measurement that we hammer in our spikes to mark the end of the excavation area. Knowing where to place our spikes for a rectangular or square shaped patio is quite simple, but for circular patios you will need to be more flexible when placing your spikes.
Next, you will tie your string line onto one of the spikes and follow the outer perimeter of your spiked out area. Following this, we then need to level these lines. We typically tie our string line to the spikes at the foundation before moving towards the spike directly to the end of the patio perpendicular to the house. Before continuing to the spikes away from the foundation, we will want to level this string line at the foundation and get this set at the correct height. Knowing the correct height depends on the height of the final pavement in relation to the threshold of the exit door.
If the door is just six or seven inches above the grade of the proposed height of the patio, you may not need to worry about creating a step into the door unless the client would like to have a landing at the height of the threshold to then step down to the patio. If the door is higher than this measurement, you will want to calculate the height and split this into equal steps leading to the door. For example, if your door is approximately 21 inches above the proposed height of the patio, you may want to split this into 7 inch step ups to the door. You then can calculate down that 21 inches from the door to set your string line to represent top of paver and level this string line across the foundation.
How to Use a Line Level
Line levels are easily lost or misplaced levels that hook onto the string line to ensure that it is level. Using these are simple and straightforward. Hook the line level at the mid point of the string line. Ensure that the line is taut and let any movement of the string line come to a stop to read where the bubble stands. Move the string line at the spike up our down to make sure that it is level and move on to the next spike in the sequence of the patio. Continue this process until the string line from spike to spike is all level. At the foundation if you adjust the string to get it level, you will want to measure down from the door threshold to ensure you held the proposed measurement depending on the number of steps and height of the steps out from the door to the pavement.
It is important to understand that the string line represents top of paver. Though before excavation, this can be difficult to represent top of paver because of any overgrown grass. Therefore, you may want to raise this by a known measurement such as 4″ and know that the string line will represent 4″ above top of paver. That means whenever you measure down from your string line in this example, you should add an additional 4″ to your measurement.
Once the foundation string line is level, you can then move on to the next spike in the sequence. This will include the same steps of leveling the string line. Once it is level, you then need to apply the slope to this run because the top of paver should not be level at the end of the patio to the paver at the foundation of the patio or else water will pool on the patio. For our projects we apply a slope of 1/8″ per foot to 1/4″ per foot.
To calculate this for your project, you will need to measure the distance of the patio from the foundation spike to the spike that is perpendicular to this. In our example, our patio is 8 feet long. We are going to apply a slope of 1/8″ per foot. That means for 8 feet, our slope is 8 x 1/8″ = 8/8″ or 1″. With our string line level, we then need to move our string line down one inch at the spike to apply that slope.
Additionally in this example, the area we want the water to run off to from our patio is immediately after the patio sloping away from the foundation. That means the next spike in the sequence should actually be level. In the final sequence of the spikes in this example would then have a 1/8″ per foot slope. This layout may change depending on where you would want the water to run.
Setting up your string line will also show you whether or not you will need to build up the surrounding area of the proposed patio and how much. If your string line is more than a few inches above your present grade and this string line truly represents top of paver, you may want to consider building a raised patio rather than building this area up depending on the space that you have to build up your yard with additional fill. This assumes your area slopes away from the foundation. This is not always the case. Sometimes the yard slopes towards the foundation and drains into the swale at the side of the house. In this case, your string line at some point will run into the slope. It is at this point that you will actually need to excavate further material into the slope and build a retaining wall in order to provide you with a flat surface to build our pavement on. You may also want your patio to be on a dual slope, one away from the foundation and one towards the swale at the side of the property. In this case, you would apply that slope to all string lines in the sequence.
Once your string lines are complete and the project elevation has been approved considering all of the above, you then have a benchmark to measure the depth of your excavation on. Knowing your depth of excavation includes adding the height of your paver, the 1″ bedding layer, and the depth of your base to know how far down from the string line which represents top of paver you should be to the bottom of the excavation area.
Projects like driveways or front walkways following the grade of the driveway do not require the string line level process. Instead, the string line would be placed at the garage floor level and end at the sidewalk or street where the driveway meets. This is the level to which the height of the pavers will be and you can skip the string line level process entirely.