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Concrete block rendered planter

NeilcannadineNeilcannadine Posts: 5
in Garden design
Hi, we are looking to build a concrete block planter and render it. The wall will be 3 blocks high all the way around and not a retaining wall, the wall will be 450mm wide, 1 block, so giving a 250mm planting area only.

my questions are: 
do I need to make the foundations cover the whole width? If so what about drainage?

do I line the inside?

similar to this:

Thanks for your help




Posts

  • NollieNollie Posts: 7,529
    Hi Neil, I’m not sure you need to have a solid bottom, if the planter is sitting on soil and you mix in stones or gravel at the bottom, hopefully any excess water will be absorbed and not seep out to eventually ruin your render at the base. If it’s sitting on a patio it might be sensible to do so so prevent it leaching and staining your tiles. Again, add gravel at the bottom or broken crocs if you have them. Either way, I would drill a couple of holes in the bottom course somewhere inconspicuous to aid drainage. You could slide in short lengths of hosepipe or similar so water is directed away from your render.

    Love the picture example, I can just imagine sitting there enjoying fragrant flowers or herbs!
    Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
  • Hostafan1Hostafan1 Posts: 34,889
    edited April 2018
    I like the concept, but feel the actual planting area is a bit of a long thing strip. Great for herbs as Nollie says, but I'd go deeper, widwthwise personally.
    Devon.
  • elderberryelderberry Posts: 118
    You only need the foundations below the blocks themselves, assuming you haven't got a solid base already like in that picture.  How deep you dig them depends on your soil, of course.
  • NeilcannadineNeilcannadine Posts: 5
    Nollie said:
    Hi Neil, I’m not sure you need to have a solid bottom, if the planter is sitting on soil and you mix in stones or gravel at the bottom, hopefully any excess water will be absorbed and not seep out to eventually ruin your render at the base. If it’s sitting on a patio it might be sensible to do so so prevent it leaching and staining your tiles. Again, add gravel at the bottom or broken crocs if you have them. Either way, I would drill a couple of holes in the bottom course somewhere inconspicuous to aid drainage. You could slide in short lengths of hosepipe or similar so water is directed away from your render.

    Love the picture example, I can just imagine sitting there enjoying fragrant flowers or herbs!


    Thanks Nollie, I have read some forums that say just a compacted hardcore base would be sufficient but others are saying foundations upto 300mm which seems excessive, houses are built on 600mm iirc!! I could run hose pipe out the rear as that would not be seen.
  • NeilcannadineNeilcannadine Posts: 5
    elderberry said:
    You only need the foundations below the blocks themselves, assuming you haven't got a solid base already like in that picture.  How deep you dig them depends on your soil, of course.
    thanks elderberry, this is my problem already on this post 2 opinions on foundations or not!! so confused! The issue is as the blocks only cover an area of 450mm wide digging one foundation would I assume cause issues with drainge, i.e. a concrete tomb! digging 2  would be time consuming and maybe not even possible.
  • Lizzie27Lizzie27 Posts: 12,494
    Hi Neil, What is the planter going to sit on - paving or soil?  If you are going to use the lightweight concrete blocks (much easier on the back!) and it's sitting on existing paving or a concrete path, then you only need to bed the first block onto mortar and you wil need some drainage holes at the back. If it's going to be bedded direct onto soil, then you need a better foundation, but you don't need to dig deep - one block's depth would probably be sufficient, again you will need some drainage holes. Hope this helps.
    North East Somerset - Clay soil over limestone
  • NeilcannadineNeilcannadine Posts: 5
    Lizzie27 said:
    Hi Neil, What is the planter going to sit on - paving or soil?  If you are going to use the lightweight concrete blocks (much easier on the back!) and it's sitting on existing paving or a concrete path, then you only need to bed the first block onto mortar and you wil need some drainage holes at the back. If it's going to be bedded direct onto soil, then you need a better foundation, but you don't need to dig deep - one block's depth would probably be sufficient, again you will need some drainage holes. Hope this helps.

    Thanks Lizzie, will be going onto soil and using the heavier blocks. Seems I will be digging a foundation. Do i do one big one, to cover both sides of the planter or 2 smaller ones so at least there would be some drainage?
  • Dave HumbyDave Humby Posts: 1,145
    Foundations only under the block line Neil. I would only go down 15 / 20cm depending on ground conditions. You'll need to line the inside of the planter with DPM or alternatively paint with Black Jack or similar. If you don't you'll soon find the nice cleanly rendered outside face will get badly stained from soil / water leaching through from the inside. 
  • NeilcannadineNeilcannadine Posts: 5
    Dave Humby said:
    Foundations only under the block line Neil. I would only go down 15 / 20cm depending on ground conditions. You'll need to line the inside of the planter with DPM or alternatively paint with Black Jack or similar. If you don't you'll soon find the nice cleanly rendered outside face will get badly stained from soil / water leaching through from the inside. 
    Thanks Dave, sounds like a good plan.


  • raisingirlraisingirl Posts: 7,093
    Unless your soil is very light, I'd probably just put one row of concrete blocks laid side on for a found strip under the blocks as DH says. I'd also chose to line the sides (not the bottom) rather than blackjack, in case you ever decide to grow herbs that you eat, or strawberries or summat.
    Gardening on the edge of Exmoor, in Devon

    “It's still magic even if you know how it's done.” 
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