They’re concrete. The wall needs to be assessed to see if its actually safe, especially if it’s above ground level. This kind of wall is not very sturdy if in poor condition. If it is deemed safe the paint needs to be removed by wire brush, chisel etc. Then it might need repointing. Or even taking down and rebuilding with the cleaned up old blocks. The blocks themselves don’t appear cracked but the joints are in a poor state. As they are in the brick wall below. You might also get the flashing checked too. Then repaint or with masonry paint. New blocks are available on ebay but they are expensive. Perforated decorative concrete blocks.

Are you in the UK? The view looks as if you are. These things were very popular in the 60s and 70s.

Oh wow, shows how much I know, I'll edit the post! It's the UK yes and I don't think any work has been done on it for years, so that would make sense. It is a first floor terrace (although there is a roof rather than a drop directly after it) also, so a good point about the safety. Thank you for your advice!

We have a similar concrete block pillar in our home that was built by a British gentleman in the 60's that were similarly crumbling. We had a concrete guy fix them by chipping out the old and building forms for new concrete.

Not a balustrade. A parapet made out of Mid-Century decorative screen blocks. I'd replace them, if possible.

Think the longer term sounds like it needs to be replacing! Any suggestions on what to replace them with? Definitely not attached to the concrete block idea

Can we see a pic of the front? Depends on house style.

AKA breeze blocks. In the right place they are lovely. I am not sure yours are. :P

Many a bookcase have been built with those...

They are called Breezeblock in the US, but a breezeblock in UK is a standard building block, or cinder block.

https://eshop.solentbrick.org.uk/Sunwall-Screen-Walling

Some more pics

As you can see at the very early stages so its super empty

Yep. Palimpsest is correct. In the UK they are not called breeze blocks. And be aware that the first floor here is the second in the US so there is a definite safety issue. If Imogen changes the appearance of the house she’ll need to check if planning permission is required. It very likely is. And, although it’s hard to see from the photo, I suspect the height wouldn’t pass the planners. Some expert advice is needed imo.

They are called screen blocks in England. The same design you have here:

Screen walling blocks

Or

Screen wall

Screenwall | Decorative Walling | Bradstone

"No, restoring such a balustrade will not work. I understand that it is large, beautiful, and aesthetic, but unfortunately, this is impossible. You will have to purchase a new stone balustrade"

@Edeline Halfhill, and you know this how? (above was copied and pasted with my quotation marls as I am certain this will be rewritten to be a spam post).

• "
  
  Edeline Halfhill
  No, restoring such a balustrade will not work. I understand that it is large, beautiful, and aesthetic, but unfortunately, this is impossible. You will have to purchase a new stone balustrade"

Rarely is ignorance so wildly on display here. Aboweld 55-1.