How to lay bricks for raised flower bed?

[Brunnie_Rich]

I'm looking to recycle bricks to build a raised flower bed, along the length of my fence (pls see pic).
I've been doing a little research on what the bricks should sit on and I'm wondering just how much foundation will be required.

Should I:

A) Lay a concrete slab, reinforced with metal bar, under gravel, using a wooden frame, 

B) Lay a concrete slab, under gravel, using a wooden frame, 

C) Lay a concrete slab on top of the compacted soil, using a wooden frame

D) Another way - please tell me  

All approaches would be looking to use a 4 inch thick concrete slab, and levelled using string and appropriate spirit levelling.

The slab would include drainage through the bottom or sides of bricks.

Here's the dug trench, still in progress. I'm aware the fence posts have been exposed to soil - previous house owners choice.
The slab will sit a few inches away from the fence line. 

Thanks in advance for any advice or insights!

[EricL]

Hello @Brunnie_Rich

Welcome to the Bunnings Workshop community. Thank you so much for joining us and sharing your question about laying bricks for a raised flower bed.

If you are stacking the bricks more than four high you will have to build a concrete slab for it. Soil compaction is also a factor when laying bricks without a cement base. However, if the flower bed is going to be very long and you will be putting in more than a cubic meter of soil, I suggest going with your first choice letter (A). Using rebar to support the cement base will prevent it from cracking under the weight of the soil. Please remember to give the cement slab enough time to cure before you put anything on top of it.

I recommend leaving a gap of 100mm between your flower bed and the fence. The gap will allow you to service the fence in case it needs repair. It sounds like a fantastic project for your garden. Any updates you can post while building your raised brick flower bed would be much appreciated.

Here is a link to a handy guide: D.I.Y. brick planter box

Let me tag our experienced members @tom_builds and @ProjectPete for their recommendations.

If you need further assistance, please let us know.

Eric

[tom_builds]

Hi @Brunnie_Rich and thanks for the tag @EricL

@Brunnie_Rich rather than laying a full concrete slab under the entire flower bed area I would suggest considering pouring a strip foundation that is twice the width of the bricks you intend to use around the edge of the bed. You can then build the wall on top of this foundation.

Doing it this way you will save on a heap of concreting work, and won't need as much reinforcing steel either. Water inside the flower bed will also be able to drain into the soil below, reducing the need to design drainage.

Looks like you've got a great project underway, I'm interested to see how it goes! 

Best of luck,

Tom

[Brunnie_Rich]

Hi @EricL , @tom_builds , 

Thank you so much for your replies and suggestions, really appreciated - it's so good to get some informed views on this.

I've only just joined this community, but loving it already!

I do like the idea of less concrete - would the same depth of 4 inches be sufficient for this approach too?
And, would that mean adding soil back to the middle section to pour, or creating an inner frame, and then back filling once set? 

Also, there's a little caveat that I didn't mention previously, that may or may not change your view - I would like to put some sort of seating in the far corner (and eventually continue another bed along the adjacent brick wall at the end of the pic there. Would this change any approach?
So to describe that further, the bed wall runs along the length of fence, soil section is partitioned just past the extra bed dug on the right, then some sort of wooden seating is used either across the top, or possibly recessed a little to accomodate wooden bench seat. (still planning this) 

If all goes well, I'll definitely update this thread with the progress

Thanks again, 
Rich

[EricL · Accepted solution]

Hi @Brunnie_Rich 

Thanks for updating us with the details of your plan. I've drawn up a quick sketch of your raised garden bed with seating based on @tom_builds recommendation of an open cement foundation. Please have a look and tell us what you think. Just to give you an approximation 4 inches is about 100mm +. Please note that the sizes indicated are for reference only, please adjust them to your needs.

Please keep us updated with your progress. We look forward to seeing your raised garden bed with seating assembled.

If you need more advice or information, please let us know.

Eric

[tom_builds]

Hi again @Brunnie_Rich,

For pouring the foundation I would create a box inside a box like in the diagram below and then pour your concrete into the space between them. You will need to stake the frames, on the corners and along the width of the outside of the outer frame and the same on the inside of the inner frame to stop the frames from moving when pouring the concrete. 

 

For foundation thickness 100mm is solid, although to build the frame you will probably find 90mm timber easier to get your hands on and for the purpose of a garden bed a 90mm foundation will be fine.

For the seat following something along the lines of @EricL's drawing is a good idea, that way you can either build a wooden or brick framed seat area. A strip foundation works best when load bearing walls run directly over it, which will likely be the set up of your seating area so no need to approach that area differently to the garden beds.

Feel free to follow up with any other questions that arise while you're completing this project.

Tom

[Brunnie_Rich]

Hi @EricL , 

Thanks for the diagrams, really helpful!
My one question at the moment would be whether this would be advisable to use gravel underneath the concrete, or if it's ok to lay the concrete directly on top of the soil. (The soil is pretty well compacted)

[Brunnie_Rich]

Hi @tom_builds , 

Thanks for this diagram and advice - using less concrete would be preferable so this sounds like a good direction, I think I'll use this method.
This is a long(ish) term project for me but I'll update this thread with the progress and I'll certainly be back asking a few questions along the way.

One extra question I've thought about whilst typing, is about the height of my bricks and the stability of retaining the soil.

I'm looking to recycle bricks reclaimed from the previous use (see attached pic). They're half sized bricks (in height, but the footprint is the same as regular house brick) and I intended to go about 8 high max (measuring 40cm, then adding 1cm of mortar in between would make it approx 48cm high total) 

Is this height ok in terms of stability? Eg. could there be too much stress from soil volume to crack the walls (i'll also be looking to render these and paint white)?

I was envisaging laying bricks in a single line in the usual manner.

CC @EricL 

[MitchellMc]

Hi Brunnie_Rich,

It's recommended to place a bed of road base or crusher dust 6-7cm thick, rake it to a level surface and tamp it down firmly all over to a thickness of 5cm. This provides a stable surface for the slab. If you don't compact the ground with road base, you'll definitely need reinforcement mesh and will probably see at least hairline cracks in the slab/foundation. 

At 48cm high, I don't believe you'd experience any issues with stability, but @tom_builds might like to give his thoughts as well.

I'll be looking forward to following along with your project. Keep us updated.

Mitchell

[Brunnie_Rich]

Hi @MitchellMc , 

Thanks for the extra advice, very much appreciated.

I was hoping to use bar in the concrete and lay the concrete on the compacted soil - if you think I should lay road base/crusher dust and it's a must do, please let me know. I'm tackling this job on my own at the moment, so looking to minimise the effort with any heavy bags of materials needed!

I've uploaded a sketched model of what I intend to be building in the space. I'm hoping to complete the seating area independently of the raised beds either side, so would be laying those concrete foundations separately over time.