Building a Raised Bed (3 Layers of Leca) Help with Preparations

[Knasputte]

Hi,
I'm planning to build an elevated planter with 3 rows/layers of concrete blocks (9*19*59cm). It will form an L-shape extending 4-5 meters in each direction. I plan to plaster and paint it white later. It will serve as a seating area-planter with a mix of plants.

My considerations:

• How deep do I need to dig out and lay gravel? Or rather the question: How little can I get away with digging out? (The ground is extremely rocky)
• Do I need to lay some form of reinforcement at the bottom? Alternatively between some of the rows?
• Should some kind of concrete/mortar be used at the bottom to make it all more stable?
• Is it necessary to plaster the inside as well, or is the outside sufficient?

Any other general advice?

SUPER GRATEFUL for all tips and advice!

 

[Knasputte]

Anyone?

 

[Stefan N]

Simply laying concrete blocks directly on the ground will not create a stable structure; you should excavate and pour a foundation for it to stand on.

 

[FreQa]

I made a couple of rectangular planting beds.

I am close to the rock, so I thought the small soil doesn't make much difference.
3 rows of lecablocks and reinforcement bars between each row. Plastered on the outside and one block down on the inside.


In your case with such large boxes, I would cast a trench with concrete along the bottom edge and reinforce it, as well as reinforce between the blocks.

 

[Knasputte]

I made a couple of rectangular planting beds.
[image]
I'm close to a mountain so I thought the little soil wouldn't matter much.
3 rows of lecablocks and rebar between each row. Plastered on the outside and one block down on the inside.
[image]

In your case with such large boxes, I would cast a trench with concrete along the bottom edge and reinforce it as well as reinforce between the blocks.

Yes, that sounds wise. I'll probably do something trench-like with concrete and rebar at the bottom from which I can then build. Does anyone have an opinion on how thick the concrete should be? Is 2 cm enough or does it need to be more like 5-10 cm?
However, the first block will be just a few centimeters below ground level, if that. Do we think it might still work?

I've dug out about 10-15 cm which I've filled with gravel and packed, and then do as above...

 

[FreQa]

Yes, that sounds smart. I will probably do something channel-like with concrete and rebar at the bottom that I will then build from. Does anyone have an opinion on how thick the concrete should be? Is 2 cm enough or does it need to be like 5-10?
However, the first block will be just a centimeter below ground level, if even that. Do we think it could still work?

I have dug out about 10-15 cm that I filled with gravel and packed, and then to do as above...

Closer to 8-10cm, the concrete will be strong enough.

My ground slopes in all directions but having the blocks a few cm below ground is okay.