Geo Fabric

Geo fabric sits between the retained soil and the drainage aggregate behind your wall. Without it, fines migrate into the gravel and clog the drainage zone, and a blocked drain is the same as no drain at all. It is the cheapest part of the drainage system and the one most often left off a materials list.

What we stock

Both rolls work out to the same rate per square metre, so the width is a practical choice rather than a price one.

Which width

• 1m suits low walls, garden terraces and raised beds, where the fabric only has to line the back of the wall and turn over the top of the drainage zone.
• 2m suits taller walls and any job where you want to line the cut, run up the back of the excavation and still have enough left to fold over the aggregate. On a 1m high wall the fabric has to cover the full height of the drainage zone plus the return, so a 1m width leaves you nothing to overlap with.

How much to order

Work on the full length of the wall, plus an allowance for overlapping joins. Our wall calculator works it out along with your gravel and agi pipe, and you can sanity check it against the drainage guide, which sets out quantities per lineal metre.

Putting it in

The fabric goes in before the gravel, not after. Line the excavation behind the sleepers, lay your agi pipe at the base, backfill with drainage gravel, then fold the fabric over the top of the aggregate so soil and fines cannot wash into it from above. Overlap joins by a generous margin rather than butting them together. The drainage management guide shows the sequence, and the cross section diagram shows where the fabric sits relative to the post, the sleepers and the backfill.

Order it at the same time as your gravel and agi pipe. Coming back for a roll of geo fabric after the gravel is already on site is a bad day.