Why slope matters on concrete

Concrete does not absorb water. Your turf system must move water across the surface and under the backing to a drain. Without a clear path, water ponds, seams stay wet, and the surface can get slick. Plan the flow first, then build the stack to match it.

Translating slope into real numbers

  • 1 percent fall equals roughly 1/8 inch per foot.
  • 2 percent fall equals roughly 1/4 inch per foot.
  • Example: Over 10 feet, 1 percent drops about 1.2 inches. At 2 percent, about 2.4 inches.

These small differences matter. Even light rain adds up. One inch of rain over 100 square feet is about 62 gallons that must find a way off the slab.

How to check your slab

Quick water test

Flood a small area with a hose and watch where the water goes. Mark any puddles after 5 to 10 minutes.

Level checks

  • Use a 6 to 8 foot level or a straight edge with shims to measure drop per foot.
  • A digital level or laser makes it easy to read percent fall across longer runs.
  • Map the flow direction and the low points. Plan the drain path to those lows.

If the slab is too flat

Use a drainage mat to create air space

Install a high-flow turf drain mat under the grass. The mat creates channels so water can move under the backing to the nearest outlet even when the surface is nearly level.

Add weep paths at low spots

  • Drill weep holes at puddling areas and along the flow line toward the drain. Typical practice: 3/8 to 1/2 inch diameter holes at each low spot and every 3 to 6 feet where water needs help moving.
  • Vacuum dust and seal the hole edges if needed to keep fines from clogging the mat.
  • Confirm slab structure, waterproofing, utilities, and post-tension cables before drilling. Follow local code.

Redirect to a real drain

If no drain exists, route flow to a scupper, channel drain, or perimeter gap that discharges safely. The drain mat should lead to that outlet without dead-ends.

Recommended build for turf over concrete

  • Turf: Perforated backing for vertical drainage.
  • Infill: Choose clean, well-graded material that does not clog. Sand blends designed for turf are common. For pets, select antimicrobial options.
  • Seams: Turf seam tape with urethane adhesive. No fasteners into the slab unless specified.
  • Underlayment: Drainage mat 10 to 20 mm thick under the entire field, especially on flat slabs.
  • Optional shock pad: Adds comfort and safety on play areas and rooftops.
  • Perimeter: Adhesive bond to clean concrete or secure to glued-down trims. Create a modest ramp or reducer where turf meets adjacent surfaces to avoid trip edges.

Edge and transition details

  • Keep the finished turf height below door thresholds and weep screeds.
  • At open edges, use a low-profile reducer or metal trim bonded to the slab, then glue turf to the trim.
  • At walls and curbs, leave a small gap for drainage and expansion, hidden under the turf edge.

Cold climates, rooftops, and pets

  • Freeze-thaw: Clear water fast to reduce icing. A drain mat plus open outlets helps.
  • Rooftops and balconies: Protect waterproofing. Do not penetrate membranes without approval. Use paver pads or trims designed for roofs.
  • Pets: Prioritize free-flowing drainage and regular rinsing. Enzyme cleaners keep odors in check.

Install steps on concrete

  1. Clean and degrease the slab. Remove loose coatings. Patch spalls.
  2. Verify flow direction. Mark low spots and the outlet path.
  3. Drill weep holes where needed. Vacuum thoroughly.
  4. Dry fit the drain mat. Cut tight to edges. Tape seams if required by the manufacturer.
  5. Dry fit turf. Align grain and plan seam locations along the fall line where possible.
  6. Glue seams with urethane adhesive and seam tape. Weight until cured.
  7. Secure perimeter with compatible adhesive or trims. Avoid blocking outlets.
  8. Add infill in light lifts. Brush between lifts for even fill and standing fibers.
  9. Water test. Watch for pooling. Add targeted weeps or small shims under the mat if you find dead zones.
  10. Final groom. Confirm doors clear and transitions are safe.

Troubleshooting

  • Ponding at seams: Check for trapped edges or infill ridges. Relieve with additional weeps and re-brush infill.
  • Slow drainage: Verify the outlet is open. Clear debris. Add more weeps along the path.
  • Odor on pet areas: Improve rinse frequency and ensure the mat outlets are not blocked.

When to call a pro

Bring in a qualified installer if the slab is dead flat across large areas, you lack a safe discharge point, or you are working over waterproofed or suspended decks. Smart design up front saves rework.