{"product_id":"20mm-drainage-aggregate-for-retaining-walls","title":"20mm Drainage Aggregate for Retaining Walls","description":"\u003ch2\u003e20mm Drainage Aggregate — The Essential Material Behind Every Retaining Wall\u003c\/h2\u003e\n\u003cp\u003e20mm clean crushed drainage aggregate is the backbone of correct retaining wall drainage. Packed behind the wall between the posts and geotextile fabric, it creates the free-draining zone that channels groundwater to your ag pipe and prevents the hydrostatic pressure buildup that causes wall failure.\u003c\/p\u003e\n\u003cp\u003eWithout adequate drainage aggregate, even a perfectly built retaining wall will fail over time. This is the material that makes drainage actually work.\u003c\/p\u003e\n\u003ch3\u003eHow Much Do You Need?\u003c\/h3\u003e\n\u003cp\u003eAs a guide, a standard retaining wall requires approximately 0.15–0.20m³ of drainage aggregate per lineal metre of wall (based on 300mm drainage zone depth). Use our \u003ca href=\"\/pages\/wallwise-pro\"\u003eWallWise Pro calculator\u003c\/a\u003e to get an accurate quantity for your project dimensions.\u003c\/p\u003e\n\u003ch3\u003eInstallation\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003ePlace geotextile fabric against the excavation face before backfilling\u003c\/li\u003e\n\u003cli\u003eLay ag pipe at the base of the wall on a bed of aggregate\u003c\/li\u003e\n\u003cli\u003eBackfill with 20mm aggregate to within 150–200mm of finished height\u003c\/li\u003e\n\u003cli\u003eWrap geotextile fabric over the top of the aggregate zone before topping with soil\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eSee our full \u003ca href=\"\/blogs\/news\/retaining-wall-drainage-structural-integrity-the-complete-australian-guide-2026\"\u003eDrainage Guide\u003c\/a\u003e for installation detail. Pair with \u003ca href=\"\/collections\/ag-pipe-for-retaining-walls\"\u003eag pipe\u003c\/a\u003e and \u003ca href=\"\/collections\/geotextile-fabric-retaining-walls\"\u003egeotextile fabric\u003c\/a\u003e for a complete drainage system.\u003c\/p\u003e","brand":"Retaining Walls Direct","offers":[{"title":"25kg Bag","offer_id":52321685438744,"sku":"AGG-25KG","price":12.0,"currency_code":"AUD","in_stock":true},{"title":"1m³ (Cubic Metre)","offer_id":52321685471512,"sku":"AGG-1M3","price":95.0,"currency_code":"AUD","in_stock":true}],"url":"https:\/\/www.retainingwallsdirect.com.au\/products\/20mm-drainage-aggregate-for-retaining-walls","provider":"Retaining Walls Direct","version":"1.0","type":"link"}