A picture would really help, but essentially what I have is a tiered garden of which the bottom 2 tiers are supported by various sections of brick and block work.
I would like to make some drastic changes but I believe a large part of the tier work is for structural support in holding back the groundwork behind it, so in order to make a better use of the space im planning on removing a few courses here, relaying a few steps there, and eventualy covering the brickwork in white render and possibly decking boards in order to create a couple of brighter and more useful seating areas.

With regards to the render – im gussing you cant just go slapping it on neat over exposed brickwork, especially when the brickwork is essentially holding back earth?
I’d imagine that water/damp from the earth would potentially cause those big stains on the render that you sometimes see?

As things stand the brickwork appears fairly clean as drainage seem quite good.

I’ve had a nightmare tracking down local firms willing to even respond let alone quoting for groundworks such as this, hence why im thinking about a DIY approach.
It would make a massive improvment to a generally useless area right behind the house.

I’d have thought render will blow pretty quickly if the brickwork is damp. You can use a waterproof base coat/tanking type render first but it might start to get a bit overkill for garden walls. Make sure you have some weep points regardless.

do you have drainage holes/pipes? Backfilled with gravel to allow water to drain to them?

DPM or bitumen coating on the back wall?

We thought about rendering a retaining wall (had all of the above) but instead opted for fixing vertical wooden battens and then spaced rustic timber cladding so it had good air flow behind. Worked very well and you can fit LED lighting behind it too if you want. If it ever needs replacing it’s a quick and easy job.

If you do want to render then maybe look at a lime based external one that can breathe?

I havent dug down to see to what extent the drainage has been provided for but the lower tiers each have a couple of drainage holes within the first course of bricks.

I have no bitumen or other coating at the moment, just bare red brick work, or bare grey blockwork (mostly brick).

I had considered floating timber clad panelling as it would be the easiest solution, however long story short, the slopes of the garden and huge hill behind our house robs a lot of natural light from the rear of the house.
By opening up the lower tier and rendering white im hoping to bounce some more reflective light into the house.

Rather than waterproof, I’d go the other way and look at highly porous/breathable coatings. Limewash etc. Same principle as old stone buildings. Hard to be sure without photos etc though (and even then, I’m no expert).

clad it with shiplap and whitewash it?

Rendering it is only likely to give you a maintenance problem in future. If you want to bounce light into the house why not clad it with acrylic garden mirror.

As a landscape gardener, several words of advice.
Rendering is hard, I still cant really do it after 10 yrs of various hard landscaping work. It probably wont stay white. Might blow.
You would have to add drainage below the grand level behind the wall and waterproof in inner face.
Basically just painting it white is a much simpler solution.
If you want a trade to do it ask a plasterer. Make sure they add proofing and use a strong mix….