Best Aggregate for French Drains: Complete Selection Guide

A French drain is only as good as the aggregate surrounding it. Choose the wrong stone and you'll have clogs, poor drainage, and a system that fails within years. Choose the right stone and your French drain will work flawlessly for decades.

This guide helps you select the perfect aggregate for your drainage project.

What Makes Good French Drain Aggregate?

The ideal drainage stone has four key characteristics:

1. Proper Size

• Large enough to create void space for water flow
• Small enough to surround pipe without huge gaps
• Typically 3/4" to 1-1/2" diameter

2. Angular Shape

• Angular stones lock together
• Prevent settling and compaction
• Maintain consistent void space

3. Clean (Washed)

• No fines (dust/dirt particles)
• Fines clog drainage voids over time
• "Clean" or "washed" stone is essential

4. Durable

• Resists weathering and breakdown
• Maintains size and shape for years
• Doesn't dissolve or erode

Best Aggregate Options for French Drains

Option 1: 3/4" Clean Stone (Recommended)

Also called: 3/4" washed, #57 stone, 3/4" clear

Specs:

• Size: 3/4" to 1" diameter
• Shape: Angular (crushed) preferred
• Fines: None (washed)

Pros:

• Perfect balance of drainage and coverage
• Completely surrounds standard 4" pipe
• Easy to work with
• Widely available

Cons:

• Can shift if not contained
• Slightly more expensive than unwashed

Best for: Standard French drains, foundation drains, yard drainage

Option 2: 1" to 1-1/2" Stone

Also called: #467, 1" clean, medium drainage stone

Specs:

• Size: 1" to 1.5" diameter
• Shape: Angular
• Fines: None

Pros:

• Maximum drainage capacity
• Excellent for high-flow situations
• Less susceptible to clogging

Cons:

• Larger gaps around pipe
• May need more stone to fill trench
• Can migrate if not edged

Best for: High-volume drainage, deep French drains, commercial applications

Option 3: 3/4" Recycled Concrete (RCA)

Specs:

• Size: 3/4" to 1" (screened)
• Shape: Very angular
• Fines: Minimal to none (specify "clean")

Pros:

• Most economical option (30–40% less than virgin stone)
• Excellent angular shape
• Environmentally friendly
• Performs as well as virgin aggregate

Cons:

• Variable appearance
• May not be available "washed" in all areas
• Slight residue possible

Best for: Budget-conscious projects, eco-friendly installations, residential drainage

Option 4: River Rock / Pea Gravel

Specs:

• Size: Varies (typically 1/2" to 1")
• Shape: Rounded (water-worn)
• Fines: Usually none

Pros:

• Attractive appearance (for exposed applications)
• Smooth texture
• Available everywhere

Cons:

• Rounded shape = less stable
• Higher settling over time
• More expensive for comparable drainage

Best for: Decorative drains, dry creek beds, visible drainage features

What NOT to Use

Crusher Run / Dense Grade

• Contains fines that clog drainage
• Compacts into solid mass
• ZERO drainage capacity

Sand

• Too fine, fills voids
• Allows no water flow
• Will completely fail

Limestone Screenings

• Basically powder/dust
• Creates paste when wet
• Opposite of drainage

Dirty/Unwashed Gravel

• Fines clog over time
• May seem fine initially
• Fails within 3–5 years

How Much Aggregate Do You Need?

Standard French Drain Dimensions:

• Width: 6–12" (typical residential)
• Depth: 18–24" (below grade)
• Pipe: 4" perforated

Aggregate Needed (per linear foot):

• 6" wide × 18" deep: ~0.03 cubic yards
• 12" wide × 24" deep: ~0.1 cubic yards

Quick Estimate Table

| Drain Length | 6"×18" Trench | 12"×24" Trench | |-------------|---------------|----------------| | 25 feet | 0.7 cy / 1 ton | 2.5 cy / 3.5 tons | | 50 feet | 1.4 cy / 2 tons | 5 cy / 7 tons | | 100 feet | 2.8 cy / 4 tons | 10 cy / 14 tons |

Formula:

(Width × Depth × Length) ÷ 324 = Cubic Yards
Cubic Yards × 1.4 = Tons

Add 10% for settling and variation.

French Drain Installation with Proper Aggregate

Step 1: Dig the Trench

• Slope: 1% grade (1" drop per 8 feet)
• Width: At least 6", preferably 12"
• Depth: 18–24" for most applications
• Smooth bottom

Step 2: Line with Filter Fabric

• Drape landscape fabric along trench
• Leave excess on sides (fold over later)
• Fabric prevents soil infiltration

Step 3: Add Base Layer of Aggregate

• 2–3" of clean stone on bottom
• Level and compact lightly
• Creates bed for pipe

Step 4: Install Pipe

• Perforated pipe, holes facing DOWN
• Maintain consistent slope
• Connect sections securely
• Route to proper outlet

Step 5: Surround with Aggregate

• Fill around and over pipe
• Leave 3–4" below surface (for topsoil/sod)
• Don't compact too aggressively

Step 6: Wrap with Fabric

• Fold excess fabric over aggregate
• Overlap seams by 4–6"
• Creates complete envelope

Step 7: Cover

• 3–4" of topsoil for lawn areas
• OR leave gravel exposed for utility areas

Comparing Aggregate Costs

| Material | Price per Ton | 50 ft Drain Cost | |----------|--------------|-----------------| | 3/4" washed stone | $35–$50 | $70–$175 | | 3/4" RCA (clean) | $20–$35 | $40–$125 | | 1" drainage stone | $35–$55 | $70–$200 | | River rock | $45–$70 | $90–$245 |

Plus delivery ($50–$150)

RCA saves 30–50% while performing identically.

Common Questions

Can I use the same stone for the whole trench?
Yes. 3/4" clean stone works from bottom to top. Some people use larger stone on bottom, but it's not necessary for residential drains.

Does the stone color matter?
Only aesthetically. For buried drains, color is irrelevant. For exposed drains (like dry creek beds), choose a color you like.

How long does French drain aggregate last?
Quality aggregate lasts indefinitely. The aggregate isn't what fails—fabric breakdown or root infiltration are typical failure points.

Should I wash the aggregate myself?
If your supplier doesn't offer washed stone, you can rinse it with a hose. But it's much easier to source clean material from the start.

Can I reuse old gravel from a failed drain?
If it's clean and the right size, yes. If it's full of fines/sediment, replace it.

Signs Your Aggregate Was Wrong

If your French drain fails early, check for:

• Fines in the stone — Muddy residue in trench
• Crushed/broken aggregate — Material too soft
• Compacted solid mass — Wrong product used
• Root infiltration — Fabric failure (not aggregate fault)
• Pipe crushed — Aggregate too large, not supporting pipe

The Bottom Line

For most French drains, 3/4" clean crushed stone or RCA is the ideal choice. It provides excellent drainage, surrounds the pipe properly, and lasts for decades.

Spend the money on clean (washed) material. The fines in cheap aggregate cause more French drain failures than any other factor.

Need drainage aggregate for your project? Smoky Mountain Sand & Gravel supplies clean 3/4" stone and RCA throughout Blount County, Maryville, Alcoa, and surrounding East Tennessee communities. Contact us at (865) 999-0857 for pricing and delivery.