9 Step Gabion Wall Build with CED Stone Fill Over a 4-Metre Boundary

Why the trench depth decides everything that follows

A 4-metre gabion run sits on whatever you give it, and a 1-metre-high wall of 100mm welded mesh baskets packed with Scottish cobble weighs close to 1.4 tonnes per linear metre. That load needs a level, compacted bearing surface or the bottom course tilts and the whole face leans within a season. Dig a trench 150mm to 200mm deep along the full 4 metres, wider than the basket footprint by 50mm each side, and take the spoil off site rather than mounding it against the back of the run.

The base layer is MOT Type 1 sub-base, laid in two lifts and whacker-plate compacted to refusal. A laser level or a long spirit level on a straightedge confirms the surface sits flat across the entire length before any mesh goes down. Skimping here is the single most common reason a gabion face goes out of plumb: the baskets are rigid, so a 15mm dip at one end telegraphs straight up through every course above it.

Setting out and the geotextile layer

String lines pinned to steel pins at each end of the 4-metre run give you the front face alignment. Run a second line for the back face so the basket width, commonly 500mm or 1000mm depending on the CED basket spec you ordered, stays constant. Check the diagonals with a tape: a 4-metre by 1-metre rectangle should read identical corner to corner, and any difference over 10mm means the set-out is skewed.

Non-woven geotextile membrane goes across the compacted Type 1 and laps up the back face of the trench. Its job is separation, keeping fines from the retained soil migrating forward into the stone fill and slowly clogging the drainage voids. A 150mm overlap between membrane sheets, weighted with a few cobbles until the baskets pin them, stops the joints opening during the build. Where the wall retains a bank rather than marking a free-standing boundary, the membrane wraps the full back face up to finished height.

Assembling the baskets and the spiral binding sequence

Flat-packed gabion baskets arrive as panels with a helical wire and C-rings or a continuous spiral binder. Fold up the four sides, stand them square against the string lines, and join the vertical edges with the spiral, threading it down through the aligned mesh apertures and crimping both ends so it cannot back out under load. CED and most UK suppliers ship 4mm or 4.5mm galvanised wire, sometimes PVC-coated where coastal salt or de-icing runoff is a factor.

The binding order matters more than it looks. Bind each basket to its neighbour along the full 4-metre run before any filling starts, so the line behaves as one continuous unit instead of eight loose boxes. Internal bracing wires, fitted across the basket at the one-third and two-thirds height, are what stop the front face bulging when the stone goes in. Fit them as you fill, not after, because reaching down into a part-packed basket to tension a brace wire is awkward and people skip it.

Lid panels stay open until the fill reaches the top. Tilt them back out of the way and bind them only once the stone is dressed level with the top edge.

Choosing and placing the CED stone fill

Fill stone for a gabion has to be larger than the mesh aperture, so for 100mm welded mesh you want graded stone in the 100mm to 200mm band. CED Stone Group lists several that suit this: Burlington slate, Scottish beach cobble, Plum slate, and a range of granites. Angular stone like Burlington locks together and resists settlement; rounded cobble looks softer but needs a touch more care at the face to avoid gaps.

Hand-place the outer 100mm against the visible face. This is the slow part and it is what separates a wall that reads as deliberate stonework from one that looks tipped from a bucket. Pack the larger, flatter faces outward, fit smaller pieces into the voids behind, and keep the courses roughly horizontal. The basket interior can take a more rapid fill, shovelled or barrowed in, but keep the density even so one zone does not settle faster than another.

Fill in 250mm to 300mm layers across the whole basket length, not one basket to the top then the next. Even layers let you fit the bracing wires at the right heights and stop the mesh distorting. A 1-metre-high basket on a 500mm width takes roughly 0.5 cubic metres of stone, and CED supplies most decorative fill in bulk bags around 850kg, so a 4-metre single-course run works out near three and a half to four bulk bags depending on the stone density.

Tamp lightly as you go. A few firm presses with a length of timber settle the fill without crushing it, and they reduce the visible drop that otherwise appears at the surface a few weeks after the build when rain has washed fines down.

Closing the lids and dressing the top course

With the stone level to the top edge, the dressing layer is the last 100mm you hand-place to give a flat, even top. Fold the lid down, pull the mesh tight against the fill, and bind it with the spiral or C-rings along every edge and across any internal divisions. Tension here keeps the top from sagging once the wall takes foot traffic or a coping load.

Where a second course stacks on top, the lower lids double as the bearing surface for the next baskets, and the courses bind together through the shared mesh. A stepped-back arrangement, setting each upper course 50mm to 75mm behind the one below, improves stability on a retaining run and sheds water away from the face.

A quick note on backfill drainage

Behind a retaining gabion, a 150mm zone of clean angular drainage stone against the geotextile carries water down to a perforated land drain at the base. Without it, hydrostatic pressure builds behind the wall and pushes the face forward regardless of how well the baskets were bound.

Finishing the run and what tends to move first

Once all eight baskets along the 4 metres are filled, bound, and lidded, walk the full face and check plumb with a 1-metre level at each basket joint. Small adjustments are still possible by redistributing surface stone before the fill fully beds in. Re-tension any spiral binder that feels slack, particularly at the top corners where the panels carry the most leverage.

The end baskets and the lower front corners are where movement shows up first. A free-standing 4-metre boundary run with no return at the ends relies entirely on its own width and the binding between baskets for lateral stability, so a 1-metre-high wall on a 500mm base is near the practical limit before you want a wider basket, a buttress return, or a stepped profile. Watch how the face behaves through the first full winter of freeze and saturation; that is when an undersized base or a skipped brace wire announces itself, and it raises the open question of whether the original 500mm width was ever enough for the height you actually built.