Raised Rendered Concrete Garden Beds - Foundation & Wall Help Needed!

Morning all,

I'm hoping some of you can help advise me on the best way to achieve my planned final design. I've been reading so much online and hearing different things around the rendering and what surface to build the wall on.

I will share my design (which has been built in Landscaping software) below, and also some pictures of the footings I've dug up.

My two issues are interlinked as my biggest concern is the moisture from the blocks damaging the final rendered wall. But I'm also looking to make my walls secure and safe, so I want the foundations to be built correctly.

Originally I was planning to cement the footings however due to the concerns of moisture building up, I believe a hardcore base would be best?

I've then read about different things regarding the rendering walls so I'm hoping you guys can advise me on the best way to do this (inside and out)?

I plan to purchase these blocks.

The plans you will see below give a rough idea of what I plan to put in the raised beds (the higher part will have some sort of topiary trees and the lower part next to water feature will have flowers).

I will be building the wall 10cm from the fence, and the total depth of flower beds will be 70cm (50cm planting area).

As you will see from the plans, there will be a water feature - this wont have a back wall behind it tho (I'm simply putting one infront of it to "complete the look".

This will all be done by myself as my first project as I want to avoid labouring costs, so I'm taking a lot of care planning it as I want to do it right.

Thanks for any help you can provide!


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  • K67K67 Leicestershire Posts: 516
    You design looks very attractive but I can't see why you can't find the information you need. YouTube has loads of videos and Google has hundreds of sites. You need a firm stable base to build on that's why you put down a concrete footing. This only needs to be about 9 inches wide. If you are worried about the moisture you could paint inside with a bitumen based paint or line with plastic but don't line the bottom.
    Hardcore inside the planting areas will help with drainage
  • srh2002uksrh2002uk Posts: 14

    That's the problem I'm having - there's so much contradicting information I'm finding, I thought I would try get advice directly relating to what I need.

    So with the concrete footing, are you saying it needs to cover my entire base, or just where the bricks will be on top?

    So effectively, half concrete and half hardcore (for the base of planters)?

  • NollieNollie Girona, Catalunya, Northen SpainPosts: 2,390
    Agree totally with K67, 8”/20cm concrete footings with the 10cm-wide blocks set in the middle,  essential for stability- so 5cm concrete footings overlap on the inner and outer face of the bricks - no need to pour concrete in the bottom of your bed, a layer of hardcore or gravel will assist drainage, as said. Lining the sides will prevent moisture from the bed blowing your render.

    I would also add a series of weep holes, roughly just below the level of hardcore/gravel. These are basically holes drilled right through or small pipes inserted in between the mortar joints to allow excess mousture to escape. Smaller scale, but my weep holes are just bits of plastic irrigation pipe pushed in while I was mortaring. It is unlined, because I plan to just paint this with a dark grey concrete stain:

  • K67K67 Leicestershire Posts: 516
    edited 30 July
    You just need footing under the blocks so not right across. So either section off or dig down a section 9 ins wide and at least 6 to 9 ins deep as long as you get to firm ground.
    You don't need anything inside the planting area that will stop water draining so no concrete! loosen up the soil in the base put in a loose layer of hardcore uf you have some to get rid of or some gravel then your soil, you need top soil not just multi purpose compost for permanent planting. 

    Edited see Nollie has beaten me!
  • NollieNollie Girona, Catalunya, Northen SpainPosts: 2,390
    Snap! 

    Only thing I forgot to say was the reason why you need concrete footings - concrete blocks are a rigid material, soil is not - so you need footings to prevent ground movement (surrounding soil swells when wet, shrinks when dry) and thus your wall cracking/falling down.

    I use a hardcore/gravel base for raised beds made from railway sleepers as the they also expand and contract, plus the sheer weight of them holds them in place. 
  • srh2002uksrh2002uk Posts: 14
    edited 30 July
    Thanks so much to both of you for your help - it's really useful! I've already dug down to the depth I planned to for the footing although I could maybe go down another couple of inches. - When I cement, should I just go straight onto the mud or do I need to put hardcore down first? - Should I use some wooden boards or something to stop my cement footing spreading into my planter space? I did read that other people have put pipes in to help with the moisture, but others have said not to because they just get blocked? I think it makes sense to put some round the back and side tho! I was planning to "test" my rendering skills on the inside of the wall, this shouldn't be an issue right? Especially if I line the inside with plastic? I'm sorry for all the questions - as said, I'm an amateur and this is my first project which I want to give a go myself.
  • K67K67 Leicestershire Posts: 516
    Boards to stop cement spreading as you need the depth as you can't do that without some form of barrier, just remove the boards when the concrete is firm enough.
    I can't say I have ever seen water coming out of drainage holes but if you put them at the level Nollie suggested they shouldn't get blocked.
    I can't see how you can put in drainage at the back and sides as you will need to build as close to the fence as you can and backfill with hardcore, gravel or concrete to support your neighbours garden.
    You might find it rather akward to render inside but give it a go. Just make sure you wet the wall before you start as that helps the render to stick.
  • srh2002uksrh2002uk Posts: 14
    Thanks again for the reply! Sorry for the poor formatting on my last message, I’m not sure where all the spaces went!

    Im guessing standard sort of 2x4 style timber should do the trick?

    Ah - so if I don’t put weeping holes or drainage within the walls, will that be an issue? Or do you think the hardcore/gravel at base will be enough for any moisture to not damage my rendered walls?

    i was actually going to mention the neighbours fences! Obviously I’ve had to dig away quite a bit of mud by them. Would you just “dump” (lack of better words) cement etc behind the adjoining walls? Or is there a better way?
  • NollieNollie Girona, Catalunya, Northen SpainPosts: 2,390
    No you need boards (planks) not 2x4 - so if your footings are 20cm deep, buy lengths of 20cm x 12mm - cheap timber decking planks, maybe. Builders use even chesper plywood braced on the outside. This is only temporary, known as form work - basically a bottomless box to pour concrete into to make your footings. A thin layer of gravel at the bottom of the box will help give the poured concrete something to bond to. Try to do it when the soil is dry, so you are not pouring onto mud!

    Weep holes are recommended, belt and braces, but not critical. If you find the bed isn't draining properly you can drill holes in between the mortar joints, at hardcore level, later on. 
  • K67K67 Leicestershire Posts: 516
    I would just dump or you could just ram soil back in depends on the gap, if it's tight it might be easier to pour a runny cenent mix in which will find its own level.
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