Top Retaining Walls Christchurch builds basalt rock retaining walls in Christchurch using the volcanic stone this city was partly built from. The Port Hills are the eroded northern shoulder of the old Lyttelton volcano, and the basalt in them has been quarried here since the 1860s.
Halswell Quarry ran from about 1861 until 1990 and supplied the distinctive blue grey stone used in the Canterbury Provincial Council Buildings, the Durham Street Methodist Church and the Sign of the Takahe. The quarry is now a council park, but Canterbury still produces basalt commercially, including from Oxford and Teddington.
Colours run from near black through dark grey, and some Port Hills stone weathers to warm browns with a textured face. That weathered look is what you see in heritage stonework across Cashmere and Lyttelton.
| Stone | Canterbury basalt from Oxford, Teddington and Port Hills sources |
|---|---|
| Colour | Blue grey to near black, some weathered brown faces |
| Shape | Angular with flat bearing faces |
| Batter | Holds steeper than rounded river rock |
| Drainage | Free draining through the voids, geotextile behind |
| Heritage match | Samples sourced before ordering on hill suburb jobs |
Basalt breaks with flat faces and sharp edges. Those faces bear on each other, so the wall locks up and holds a steeper batter than rounded river rock ever will. On a tight section where you cannot afford to lose a metre of yard to a leaning wall, that matters.
It also means a basalt wall drains freely through the voids, so water never sits behind the face.
On the hill suburbs there is a lot of existing stonework, and a new wall that does not match the neighbours looks wrong immediately. We take photos of what is already there and get samples from the supplier before we order, because basalt colour varies between sources.
On the flat, basalt reads as a deliberate design choice rather than a local material, and it pairs very well with dark cladding on newer builds.
Every wall we build gets drainage. At least 300mm of clean free draining metal, a perforated coil at the base running to a real outlet, and geotextile over the top so silt cannot block it. It is not an optional line on our quotes.
Halswell Quarry closed in 1990 and is now a park, so no new stone comes out of it. Canterbury produces basalt from other quarries and suppliers can usually match the look closely.
Yes, it is one of the better rocks for gabions because it is hard and angular, so the pieces lock together inside the basket.
No. It is volcanic rock and it handles Canterbury weather without any help. Moss on the shaded side is normal and most owners leave it.
Our old wall was rotten right through and leaning into the neighbour's place. They pulled the lot out, put proper drainage behind the new one and had it finished in three days. Swept the site clean every afternoon before they left too. Tidiest crew we have ever had here by a long way.
They sorted the consent, which was the bit I was dreading. Dealt with the council so I never had to, and kept me in the loop the whole way through. The driveway sits right above it and has not shifted a millimetre.
Steep section, shocking access, and they still made it look easy. They suggested two smaller walls instead of one big one, which saved us thousands in engineering fees. The terrace in between is now my favourite part of the whole garden.
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