Drainage Gravel and Filter Stone

Single-size grading is the whole specification

A 20–40 mm single-size stone holds around 30–40% void space. Add 5% fines and that void collapses. We wash and screen drainage grades separately from decorative production so nothing carries over.

Choosing the right size for the application

20–40 mm is the general land drainage and soakaway size. 10–20 mm suits narrow trenches and pipe surround. 40–75 mm handles high-flow soakaways and rubble drains where volume matters more than trench width.

Angular or rounded for drainage

Angular stone locks and holds trench walls but has slightly lower void space. Rounded stone flows better around pipes and gives higher voids but can settle. Pipe surround usually specifies rounded; structural backfill usually specifies angular.

Geotextile use

Wrapping the drainage stone in a geotextile stops surrounding soil migrating into the voids. Without it, even perfectly clean stone silts up within a few years. It is a small cost that protects the whole installation.

Testing and documentation

Where a project specification requires it, we supply grading analysis and washing confirmation with the shipment so the consultant can sign off without site testing.

Volume calculation

A trench 300 mm wide by 600 mm deep needs about 0.18 cubic metres per linear metre, roughly 0.28 tonnes. Order 5–10% extra for settlement and trench overbreak.

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 drainage gravel

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