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!

[petriwhite]

Hi @Brunnie_Rich, awesome project and thanks for posting the updates through here.

I'm looking to build something very similar myself - keen to hear how much rebar you put into the strip footing and where/how your placed it? did you opt for mesh, or just rebar rods running through the structure? If you used rods, did you place them through the centre depth of the slab or nearer the bottom? Any tips would be great!

Thanks, Pete

[Jason]

Hi Pete (@petriwhite) 

Great to see you've been inspired by @Brunnie_Rich's project. Hopefully they will be able to come back to you soon regarding your questions. I'm sure our resident Bunnings D.I.Y. expert @EricL would also be happy to assist as soon as possible. Feel free to share more details about your project and post as many questions as you wish. 

You might also to check out our Top 10 most popular raised garden bed projects shared by other community members.

Welcome to Bunnings Workshop.

Jason

[Jewelleryrescue]

Hi @petriwhite

The  best  steel for you to use is Trench mesh  Reo 

Jack 1800 x 200mm Light Duty Reinforcing Trench MeshI/N: 1060367

$22.85

It is  reo bars welded together to make  concrete extra strong under load.The reo mesh is 200mm wide great for a  brick wall. basically the function of the steel is even if the ground moves under the weight of concrete and bricks and cracks there is no drama as the steel locks it all together.  Raise the steel middle way in the cement to rust proof it and gives cement maximum support,  Lift the steel with any thing like bits of rock or broken brick  or buy  reo stools/chairs (plastic spacers designed to lift steel up into the concrete.

Do line the trench with plastic as it makes concrete when poured a smooth shape which adds  strength as  a uniform shape. Use any plastic laided flat.

I notice in the picture cement  path on end and a  brick wall the other end. This is where  reo bar come into play  I would  drill with a  rotary hammer drill,  holes to insert 300mm lengths of  reo  bar into the holes to act as pins to the existing concrete and  wall footing this will hold you new  footing at the wall and path level even if the ground sinks a bit.

Have you ever cursed   council foot paths sunken in spots and raised in others they should have pinned into each new slab and used expansion  joints.

Expansion joints foam every 5 to 10 meters and between old and new work you may not need it.

[EricL]

Hello @petriwhite 

While we are waiting for @Brunnie_Rich to confirm the size of the Reo bar, would it be possible for you to show how big of a footing you are planning to build? If you are building a narrow footing, then I suggest using Australian Handyman Supplies 12mm x 2m Reinforcing Round Bar in combination with Jack 25 - 40mm Plastic Reinforcing Bar Chair.

I propose having the reo close to the center mass of the footing to provide maximum support. My best advice is to make sure to use WD40 on the frame as a release agent for the formwork.

If you have any other questions we can help with, please let us know.

Eric

[Brunnie_Rich]

Hi @petriwhite , 

Thanks for asking, hopefully sharing my experience will help.

I did use some bar in there, nothing too heavy duty. Looking back at the pic, I can see I used a slightly thicker bar around the edge, and slightly thinner in the middle. It was for a brick planter, and has worked out well. 
Top tip for the rebar is to make sure you place it on some stones, to raise the height of it to ensure it sits in the middle of the concrete (vertically). That way it won't sit on the floor/bottom of concrete, and weaken the overall slab. I also used wire to mesh the off cut bar together, to hold it in place when pouring the concrete in - this is also a must I'd say. 

Other tips -
- Mix the concrete well - not too wet (weakens it), not too dry (won't pour) - Youtube was my friend for this as you'll get a sense of the correct consistency. 
- Make sure you use a sufficient thickness of wooden frame (pic shows a good thickness). My first slab I skimped and used a thinner frame - I found I needed to quickly add more pegs to brace it as it bowed after pouring the concrete. I got away with it, but made it more stressful for a first time effort.
- I used a canola oil spray (cheap and worked) on the inside of my wooden frame before pouring, where it came in to contact with the concrete. Made it easy to remove the frame after the concrete had set. 

I made this slab over a year ago now, all is good and solid!

Good luck with your project

[petriwhite]

Thanks Eric. We are planning to build quite a long series of raised beds against our fenceline.

The beds will be built from 10 series concrete block, with a similar style render finish to @Brunnie_Rich‘s project.

We have a ~30m fenceline, and are planning to build the beds along ~20m of this. The beds will be ~80cm width (ie two standard blocks), and will be three courses of block high (~60cm). Each bed section will be ~1.8m long (ie four standard blocks and 2x dividing walls)
We have dug the trench (~25cm wide) for the footing for the back line of the beds (couple of photos attached pre-and post-road base), and have laid a layer of compacted road base to sit the concrete footing on. Do either you or @Jewelleryrescue  have any recommendations for the concrete footing depth (we were planning 12cm, with rebar at mid-height), and whether both the sides and base of the trench should be lined with plastic or just the base. We are planning to pour the concrete footing in sections (either 1 or 2 bed sections at a time, ie 1.8 / 3.6m sections), with expansion joints between each. Do you have any recommendations for expansion joint foam, and/or is it possible to fill with the road base instead? 

 

many thanks - really appreciate the advice so far.
pete

[Jewelleryrescue]

Hi  @petriwhite 

Hi am a bit confused with your plans. If you are going to build a bed  80cm wide with  bricks all round  i think i am reading for you desired results where is the foundations for the 80cm width?  I would  highly  recommend  digging and pouring each  section or two sections as you plan including the sides and front footings at the same time so the footing is done and ready to go in one pour.

As it looks now you are starting with one  long back wall so that makes footings weaker if you try join into the back wall with the side footing later.  But I might have miss understood your planning so sorry if I have. Your  plans for expantion  joint are good use expansion foam  every 2 sections  is plenty.

Consolidated Alloys 125mm x 10mm x 25mt Roll Foam Expansion Joint I/N: 1060549 $35

Expantion foam has a  bunch of home uses for the extra you will have.

As  you prepare footings for one or two bays have steel protruding out down your 20 meter brick line 30to 40cm  long  lengths and push your expansion foam onto the steel to create an expansin joint ( Foam.) but at the same time tie the footings together so they move as one if they linked and move together.

I prefer 250mm deep minimum for three bricks high but you all ready dug 12cm and filled it with road base. But you might be able to compensate with a  very strong concrete mix . Plants are powerfull and there roots  can crack footings and lift and twist them with ease, Maybe you neighbours plants?

I have a tree and it grew  from sappling 25 years later,  now its  root lifted my extra think footings of 300 mm square up by 40mm but the brickes are as good as  I layed them as an example. A weak footing would have ripped apart bending the steel trashing the wall needing rebuild.

No road base is required for concreting your better of mixing it in with  the cement and pour it in to a deeper footing. Ie  your planned 120mm plus your road base depth =? lets say 50mm so final cement footing is 170mm thick. Is  better and stronger.

I  am just about to build a 2 besser brick raised  garden  bed with capping I will dig all the footing, line it  with plastic (Smooth concrete is stronger by shape and more impervious to water.) lay trench mesh and lift it with  concrete stools or brick chunks mine will be 250 x 300 deep  my choice there (general cement mix) set the form work to parellel at correct  height and pour.  The whole footing ready for bricks.

No release agent is  ever needed  in DIY projects a simple tap to the wood will pop it off  after a week of drying. If you try to release footing to soon concrete can be damaged while green maybe thats  how the release myth started.  or   Oil it if you want 

[MitchellMc]

Hi @petriwhite,

A Besser block wall only requires a compacted base, as does a concrete footing. Have you compacted the trench with a machine? Having a base that doesn't subside is the most important factor. The first course of blocks is laid onto a bed of concrete mix, but this is predominantly to bed them in place at the correct level. A 12cm slab with reo should be fine, but as @Jewelleryrescue has mentioned, thicker is often better.

Please let us know if you have any questions.

Mitchell