How would you top this garden wall?

[Johnny Penstemon]

Hi all, first post from a gardener turned novice DIYer. I’ve got an odd double wall set-up as per the first pic, an old brick wall on the right and a more modern wall on the left. Despite the rubbish pic, both are sturdy.

What I want to do is put some soil in the central void and plant in between the two walls.

But first I want to smarten the modern wall on the left, covering and levelling the exposed brick top before painting. A friend suggested laying slate tiles along it at a slight angle, but I want to be able to still walk along it.

Does anyone have any simple, inexpensive suggestions? I guess I could lay cement but I have no idea how to achieve a smooth level surface.

Any ideas gratefully received! Cheers, Johnny

 

[Johnny Penstemon]

I should add that the void only extends about 90 cm down between the two, so deep enough to plant a line of bulbs and perennials.

 

[conny]

The first thing I notice is that the 'modern' wall was not laid by a brickie.
Two reasons. 1/ It is not straight because the inner leaf bows, which suggests it hasn't been tied in properly. 2/ The bricks have been laid upside down. That V shaped hollow is known as the 'frog' and should be facing downwards. This prevents water seeping in and forming pools in the hollow. In cold weather these pools of water can freeze as ice blocks. As ice expands it can de-stabilise the whole structure and cause the wall to fail with the possibility of collapse.
Putting flowers/plants in between could exacerbate this problem if they are strong root specimens that could potentially push the bricks out of position.
I would seriously consider not putting anything in there but instead fitting coping stones which span both walls and cover the gap entirely. This will prevent rainwater collecting in the frogs and also between both walls and causing destabilisation if it freezes and also stop wild seeds being blown in and sprouting weeds.

 

[Johnny Penstemon]

Hi Conny

Thanks so much - so much useful info in one post! This got me thinking first:

“Putting flowers/plants in between could exacerbate this problem if they are strong root specimens that could potentially push the bricks out of position.”
- The plants will be very shallow rooted like ornamental grasses (Stipa tenuissima since you ask ) so I don’t think this will be an issue. (I don’t know my bricklaying, but I’m reasonably savvy on the plant side.)

Then there’s this very good point:
“..coping stones which span both walls and cover the gap entirely... will prevent rainwater collecting in the frogs and also between both walls and causing destabilisation if it freezes”
- If I top the exposed frogs (perhaps I could lay a soldier course atop if nothing else) hopefully they’ll cease to be a weak point.
- If the relatively shallow void (90cm approx) between the walls was filled with soil/compost, could this act in the same way as the coping stones since, while not as dense a material, it’ll still absorb rainwater and prevent it from freezing. The walls could be lined with plastic and the base with a weed proof membrane.

Maybe I’m being an optimist, but you”ll gather I’d love a cheeky and idiosyncratic little row of plants there. But granted I mustn’t unduly weaken the walls, so I’ll do some pondering. Thanks again. And I had no idea the bricks were upside down!

 

[conny]

If you fill the void try not to use clay based soil as I think this retains more water and, if it freezes could disturb the top layer or two of bricks. I don't think you need to line it with plastic. So long as you use tender shooting plants then you will probably be alright, at least for a number of years.
Some pics when you have finished would be nice.

 

[Johnny Penstemon]

@conny Thanks again and yes, I’ll use a free-draining soil mix. Looks like I’ll be practising my brick laying and adding a soldier course atop. I’ll post a pic or two when it’s done.