Backfilling hole for laying lawn

I've pulled up some rotten decking in our small garden with the intention of laying lawn. From what I can gather from the internet, I need a depth of 10-15cm topsoil but I have a hole of 32cm depth to fill. The good news is the whole area is only approx 2mx2m. The hole is a concrete basin which appears to be broken open, presumably for drainage, in the centre. I'm aware that I need to let the topsoil settle for 6-8weeks before laying the lawn so am eager to get going but I've no idea how to fill the gap. Can anyone guide me in the right direction?

Posts

  • BobTheGardenerBobTheGardener Leicestershire, UKPosts: 7,925

    I'm finding it difficult to visualise exactly what you mean from the description.  Can you upload a photo?  If you mean the whole area is 2m x 2m x 32cm deep but you only want to buy 10-15cm of topsoil, then one option is to put 15-20cm of ballast, gravel, sharp sand or similar free-draining cheap 'filler' material down to provide drainage then a layer of topsoil to the required level on top.

    A trowel in the hand is worth a thousand lost under a bush.
  • DovefromaboveDovefromabove Central Norfolk UKPosts: 55,117

    I'm confused - do you mean that there is a hole of 32 cm deep in the middle of an area 2m x 2m?

    “I am not lost, for I know where I am. But however, where I am may be lost.” Winnie the Pooh







  • FairygirlFairygirl west central ScotlandPosts: 25,301

    Has the concrete basin originally been a pond, which has then been decked over?

    I'd agree with Bob's solution. Fill with ballast to get the levels right and consolidate it well, as it will  settle a bit just like the soil.

    It's a place where beautiful isn't enough of a word....


  • Hi. Thanks for your posts. Just to clarify, it's a raised area divided into 2 beds, a paved area and a decking area. I just double checked the exact measurements of what was the decking and it's a little larger at 2.6x2.4m. This area is a consistent 32cm deep all across although whereas I'm hitting concrete around the edges, the centre is broken through to soil presumably for drainage.

    So based on Bob's suggestion it sounds like I need to find some gravel or sharp sand - presumably from a garden centre?, to half fill it and then fill the other half with topsoil. Unless of course I should fill the whole thing with topsoil? Seriously, I don't really know what I'm doing here!

    If I do lay two layers as suggested, can I lay them both at the same time or do I need to leave to settle between layers? Another daft question perhaps, but Fairygirl, when you say 'consolidate' , does that mean I have to do anything to it other than just waiting?

    Many thanks for your help so far!
  • BobTheGardenerBobTheGardener Leicestershire, UKPosts: 7,925

    That does make it a bit clearer.  As there is concrete around the edges I think you do need a good drainage layer.  The cheapest would be to get the ballast etc from a local builder's merchant.  Free-draining materials such as ballast, gravel, sharp sand, pea shingle etc all cost about the same - it's the delivery cost you need to keep an eye on.  To put a 15cm layer down in an area of 2.6 x 2.4m will require almost exactly 1 cubic metre, which is the size of a "tonne bag" (aka "builder's bag" or "Jumbo bag".)  You don't need "decorative" materials which cost more.

    A trowel in the hand is worth a thousand lost under a bush.
  • FairygirlFairygirl west central ScotlandPosts: 25,301

    Bob's right - builder's merchants are always cheapest. You're just looking to get the hole filled as firmly as possible so that the soil you put on top doesn't sink, so that's all consolidate means - getting it as firmly bedded down as you can first. If you put a bit of weed suppressing membrane on top of it, before you put the soil on, it will help prevent it washing through as well. The ballast will settle a bit too, especially if there's a lot of rain so make sure you get enough. As Bob has shown,  you always need more than you think you will!image

    It's a place where beautiful isn't enough of a word....


  • Great! Thanks for your help. Now I just need to work out how to get two tonne bags of material through the flat!
  • Beefmandu wrote (see)
    Great! Thanks for your help. Now I just need to work out how to get two tonne bags of material through the flat!

    Have it delivered to your drive, then keep nipping outside to fill your trouser pockets with some of the soil, then go into the garden and scatter it out of your trouser leg. Just like they did in The Great Escape.

  • FairygirlFairygirl west central ScotlandPosts: 25,301

    LF image

    Oh dear - that's a bit tricky image

    Is there no access nearby at all? Perhaps you can get some friends to bring some buckets and spades...imageimage

    A large amount of plastic laid down on the floors will be a must I think!

    It's a place where beautiful isn't enough of a word....


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