Pointer needed on flint rendering walls

[tessaanddennis]

Seen your useful comments of a few years ago. As an amateur (with some building experience) I have to repair a typical 1930 2’ flint wall made up of a 4” brick backing (bricks laid on their edge unfortunately – so not that strong!) holding back a 1½ ’ raised garden behind, with a flint wall facing (in cement I think almost certainly), NOT tied to this base wall. Wooden post every 2m’! All a bit basic I know, but that is what I have to work on. My problem - 2 ‘panels/sections’ have gone + 1 post, primarily I think because the cement cap (the only thing seemingly holding the two ‘walls together!) slowly gave way, and one post, and to some extent garden plants, have exerted pressure on the whole structure over the past 80 odd years. I have taken off the remaining capping cement and the 2 flint constructed facing ‘panels’, and surprisingly the brick backing wall is still sound, apart from the 1 – 2 top layer of bricks!
On the basis of your comments and others here, I am confident I can repair it, but a little further advice/detail might help prolong its life beyond mine I hope.
1 cement:3 (sand?) mix was mentioned. Then 1:2:9, but similar advice on mixes seems to discredit any cement with lime. So I am back to sand/cement – but what mix? 1:3 does seem very strong! Inflexible?
What type of sand should I be using - The original looks slightly gritty?
How much sand would I need per sq m of wall? I guess I have to build about 3m of flint wall.
Any other comments/pointers would be appreciated.

Speaking as the owner of a very large flint wall (Listed GII), we had to rebuild a section which was demolished by a tree.

There are two main methods of constructing a flint wall:

1. The entire wall is constructed using flint rubble (this relies upon timber shuttering being constructed either side of the wall to hold until the mortar goes off). This is not normally used now.

2. The second is to construct a brick core (although some use concrete blocks) as described earlier in the thread. This core should have wall ties or similar protruding into the panel to provide some support for the flints. Strictly, I would use a 3:1 sand:lime putty mix. If you are going to use cement, then you might as well use the panels you already have....but the look will not be the same. I'm not a professional builder (just a householder interested in historic building conservation) and I managed to make my own lime putty and mix my own mortar.

The mortar is usually 'thrown' at the wall and the flints bedded into this. You will probably only build 1ft or so at a time since the mortar will need time to harden (doesn't happen as quickly as cement).

When a panel is finished, the face of the flints is normally brushed (with a stiff bristle) whilst misting with water (garden sprayer will do fine). This brushing both cleans the face of the flints and also exposes the aggregate in the mortar. It also leaves more of the flint face showing (look at an old flint wall for an example)

You do not have to use knapped flints - styles vary by region and there are many different types. If you want knapped, these are still available from suppliers like Mike Wye Associates.