DecorativePebbles.comDecorative pebbles & landscaping stone supplier

French Drain Rock and Washed Drainage Aggregate

A french drain only works if the stone around the pipe stays open. The single biggest cause of failure is aggregate that arrives with dust and fines still in it, which wash down and blind the voids within a season. Everything we ship for drainage use is washed and screened.

  • Washed to remove fines that clog the drain
  • Angular 20–40 mm for maximum void ratio
  • Rounded river grades where pipe protection matters
  • Bulk bags for trench-side placement
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Washed angular drainage stone surrounding a perforated pipe in a trench

Available sizes

  • 10–20 mm
  • 20–40 mm
  • 40–60 mm

Applications

  • French drains and land drains
  • Soakaways and infiltration trenches
  • Perimeter foundation drainage
  • Retaining wall backfill
  • Sports field and green roof drainage layers

Typical buyers

  • Drainage contractors
  • Builders merchants
  • Landscape supply yards
  • Distributors

Why washed stone is non-negotiable

Unwashed crusher run looks cheaper per tonne but carries a fines fraction that migrates into the voids as soon as water moves through the trench. Once the matrix blinds, the drain carries a fraction of its design flow. Washed aggregate keeps its void ratio and gives the drain the working life it was designed for.

Angular or rounded — which to use

Angular stone holds a higher, more stable void ratio and resists settlement, which is why it is the default for structural drainage. Rounded river stone is gentler on membrane and pipe and is easier to place by hand in shallow garden drains. Both are available; the choice usually comes down to whether a machine or a person is doing the backfill.

Sizing against your pipe perforations

The aggregate must be larger than the pipe slots or it migrates into the pipe. For standard perforated land drain, 20–40 mm is the safe general choice. Where slots are wide, step up to 40–60 mm. Wrapping the trench in geotextile is still recommended in silty ground regardless of stone size.

Packing that suits trench work

Most drainage buyers take jumbo bags because they can be craned or forklifted to the trench line and cut open in place, which avoids double handling from a loose stockpile. Loose bulk still makes sense on large civil sites with a loading shovel already on hire.

Consistency between deliveries

Contractors judge a supplier on whether the second load matches the first. We hold a sealed reference sample against your approved batch, so repeat orders are screened to the same band rather than whatever the crusher happened to produce that week.

Wholesale, bulk and export details

This product is supplied on the same commercial basis as the rest of our range: quantity confirmed against container payload, packing quoted separately and documentation prepared to your broker's brief.

Questions buyers ask about french drain rock

What size stone is best for a french drain?
20–40 mm washed angular aggregate suits most installations. It is large enough not to enter standard pipe perforations, holds a high void ratio and is still easy to shovel and level in a trench.
Can I use pea gravel in a french drain?
You can in light garden applications, and it is easy to place, but the smaller rounded particles give a lower void ratio and settle more. For anything carrying real volume or sitting under a structure, 20–40 mm angular stone performs better.
Does drainage stone need to be washed?
Yes. Fines are the main cause of premature drain failure. Washed material costs slightly more per tonne and repays it many times over in service life.
Do I still need geotextile if the stone is washed?
In silty or clay soils, yes — the fines come from the surrounding ground, not the stone. A wrap of non-woven geotextile around the trench keeps soil out of the aggregate matrix.
How much drainage stone will I need?
Multiply trench length by width by depth for cubic metres, then allow roughly 1.5 tonnes per cubic metre for washed angular stone. Send us the trench dimensions and we will convert it and tell you how it loads into containers.
What packing do you supply?
Jumbo bags of roughly one tonne are the most common for drainage work, with 20–25 kg bags available for merchant resale and loose bulk for larger civil orders.

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