Artificial Grass Sub Base, Explained

Sub base by use

Depth is measured after compaction, not as loose material. The two-layer lawn build most Southern California crews run is 2 to 2.5 inches of crushed rock or road base compacted first, then a 1 to 1.5 inch decomposed granite finish coat screeded flat and compacted again. The road base does the structural work; the DG gives you a smooth plane so the turf backing sits flat and the pile reads even.

The three materials, and when to use each

Class II road base is 3/4-inch minus crushed aggregate with fines. The fines lock the stone together under a plate compactor, which is why it holds a grade and holds nails better than anything else on the list. It is the default structural layer for lawns, greens and commercial landscape.

Decomposed granite is finer, spreads and screeds easily, and is the standard finish coat in Southern California, Arizona and Nevada. Order plain DG. Stabilized DG (the kind sold for pathways) has a binder that turns hard and stops draining, and it does not belong under turf. On sandy, well-drained soil some crews run DG for the full 3 inches; it compacts softer than road base, so hold the depth at 4 inches if you do.

Washed crushed stone (3/8 clean or 3/4 minus with the fines rinsed off) is the pet-turf base. It drains several times faster than road base and does not hold urine the way fines do. Pair it with a permeable or perforated turf backing and zeolite infill, and the odor complaints stop before they start.

How much base to order

Cubic yards equal square feet times depth in feet, divided by 27. Aggregate yards run roughly 1.4 tons per cubic yard, so a 1,000 square foot lawn at 3 inches is about 9 yards or 13 tons before compaction. Order 10 percent over the table below to cover compaction and the low spots you will find once the grass is stripped.

Columns: cubic yards, then tons at 1.4 tons per yard. Ask your aggregate yard for the actual density of their road base; DG runs lighter.

Grade, water, compaction

Excavate 3 to 4 inches below the finished height of the surrounding hardscape so the turf ends up flush, then cut a fall of 1 to 2 percent, about one inch of drop per 10 feet, away from the house. Spread the base in lifts no thicker than 2 inches, dampen each lift until it holds a print without puddling, and run a vibratory plate compactor in overlapping passes in two directions. Done right you can walk it in boots and leave no mark. Screed the DG coat with a straight board, compact again, and lift the turf onto it. Never drag a roll across a finished base; it gouges the plane you just built.

Weed barrier and gopher wire

On a lawn the weed barrier goes on the excavated soil, under the base, seams overlapped 6 to 8 inches and stapled. It stops the weeds that would otherwise push through the drain holes in year two. On pet turf the rule flips: no fabric directly under the turf, because it holds moisture and urine odor. If the site needs a membrane, it goes below the sub-base.

Gopher wire is galvanized hardware mesh laid on the soil before the base in gopher country, which covers most of the Inland Empire, the High Desert and the Central Valley. Without it a gopher tunnels under the base, the base collapses into the run, and the turf sinks in a line you can see from the street. Both accessories ship on the same truck as the rolls; ask your rep to add weed barrier (6 by 300 foot rolls) and gopher wire (4 by 100 foot rolls) to the order.

Five base mistakes that cause callbacks

• Too thin. Two inches of base over clay heaves and dips with the first wet winter. Hold 3 to 4 inches.
• Not compacted. Raked-smooth is not compacted. Footprints in the base become footprints in the turf.
• No fall. Flat base, standing water under the turf, algae and smell. Cut the 1 to 2 percent.
• Fabric under pet turf. Traps urine. Move it below the base or leave it out.
• Rolls dragged across the finish coat. Every gouge is a low spot. Lift and place, then let the turf relax 30 to 60 minutes in the sun before cutting.