If a synthetic lawn ever ripples, sinks, or puddles, the cause almost always traces back to the base. This guide covers excavation and grading in the depth they deserve, so the foundation under your artificial grass installation stays flat, firm, and free-draining for the life of the turf.
Why the Base Does the Heavy Lifting
Turf is just the visible skin of the system. Everything you value about a finished lawn, the flatness, the drainage, the way it holds a footprint without depressions, comes from the compacted aggregate underneath. A perfect roll of turf laid on a poor base will disappoint within months. A modest turf on an excellent base will look sharp for years.
Getting the base right means three things done well: excavating to the correct depth, grading to a consistent slope, and compacting in thin layers. Skip or rush any one of them and the other two cannot save the job.
Step 1: Set Your Excavation Depth
Excavation depth depends on your finished height. The goal is for the top of the turf to sit flush with adjacent patios, paths, and driveways, not proud of them and not sunken below.
- Measure the thickness of your chosen turf, including pile and backing.
- Add your planned compacted base depth, generally 3 to 4 inches for residential lawns.
- Excavate to that combined depth below the finished grade you want.
- In heavy clay, poor-draining soil, or areas with vehicle or heavy foot traffic, dig deeper and plan a thicker base.
Remove all sod, roots, and soft organic soil. Organic material breaks down over time and settles unevenly, so anything that can rot needs to come out.
Safety note: before excavating, call 811 to locate buried utilities. Digging into a gas or fiber line is dangerous and expensive.
Step 2: Grade the Subgrade for Drainage
Grading is the art of shaping the ground so water leaves the lawn instead of sitting on it. Even permeable turf and open base cannot compensate for a subgrade that traps water.
- Establish a fall of about 1 to 2 percent, roughly a quarter inch of drop per foot, away from any structure.
- Use string lines and a line level, or a long straightedge with a torpedo level, to check the slope across the whole area.
- Direct the fall toward planting beds, a drain, or an area that can absorb runoff.
- Smooth out any low spots that would collect water under the turf.
On flat lots with nowhere for water to go, you may need a French drain or a channel drain at the low edge. Plan that before you build the base, not after.
Step 3: Choose and Place the Aggregate
Base material needs to compact tightly yet still drain. Most successful artificial grass installation projects use one of a few proven aggregates.
Common Base Materials
- Crushed aggregate base: angular crushed stone with fines that lock together under compaction. A workhorse choice for structure.
- Decomposed granite: a finer material that screeds to a very smooth top surface, often used as a leveling course.
- Clean crushed stone with no fines: used where maximum drainage matters, such as pet areas, sometimes topped with a thin leveling layer.
A common approach is a structural layer of crushed aggregate topped with a thin finer course for a glass-smooth finish. Spread the material in lifts of about 2 inches rather than one deep dump.
Step 4: Compact in Thin Layers
Compaction is where flat lawns are won. The mistake that ruins bases is spreading the full depth at once and compacting the top while the bottom stays loose.
- Lightly mist each lift with water. Damp aggregate compacts far better than dry.
- Run a plate compactor over each 2-inch lift in overlapping passes until the surface stops moving under the plate.
- Add the next lift and repeat until you reach your target compacted depth.
- Screed and compact the final leveling course so it holds a footprint only faintly.
Aim for a firm, dense surface. As a field check, walking across finished base should leave barely any impression. Confirm the exact base depth and compaction expectations against your turf manufacturer's installation spec, since those figures are tied to the warranty. Get this stage right and the rest of the artificial grass installation is comparatively easy.
Safety note: plate compactors are heavy and vibrate hard. Wear boots, hearing protection, and gloves, keep your feet away from the plate, and get help moving it on and off the trailer.
Common Grading and Base Mistakes
- Excavating too shallow, leaving the finished lawn sitting high above the patio.
- Leaving organic soil in place, which decomposes and creates dips.
- Compacting one deep layer instead of several thin lifts.
- Building a dead-flat base with no slope, so water pools under the turf.
- Skipping the water during compaction, so the aggregate never fully densifies.
Frequently Asked Questions
How deep should the base be?
Most residential lawns use a compacted base of roughly 3 to 4 inches, with more depth in poor-draining soil or high-traffic areas. Your turf manufacturer's spec is the final authority, so verify before you order aggregate.
Can I use regular sand as a base?
Plain building sand is a poor structural base because it shifts and does not lock together. Angular crushed aggregate or decomposed granite compacts into a stable surface, while sharp sand is best reserved as a thin leveling course.
How do I know the base is compacted enough?
A properly compacted base feels firm underfoot and takes only a faint footprint. If your heel sinks in or the surface shifts, keep compacting, and add water if the material is dry.
Let Us Handle the Hard Part
Excavation and grading are the least glamorous and most important parts of a synthetic lawn. If you would rather not wrangle a compactor, our crews build bases every day. See our services or get a free quote to talk through your yard. Reach us directly at 877-692-5349 for a free assessment.