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Laying slabs on clay soil - done the professional way !

Laying slabs on ...well...mud i suppose..certainly clay soil. Standard issue slabs - likely be 2 by 2 .

Quarry dust? throw it down, throw sand down? ..

Dig out some clay soil, and concrete it ( worst case scenerio ).

Any thoughts on decent method to lay these slabs?, throw down sand and hope for best ..


  • Jason millyJason milly Posts: 546

    I would lay some stone down tamp it down and then lay on a bed of mortor , the stone will give a good base and for drainage .

  • LeifUKLeifUK Posts: 573

    There's a video on this site, with Monty Don I think. I think they laid hardcore, then placed each slab on a blob of mortar, allowing adjustment. Too thin a base and it'll move in a year, but on clay it'll move anyway unless very thick. 

    What are the slabs for? I laid slabs on three inches of sand on clay. It works as a rustic simple path. 

  • Invicta2Invicta2 Posts: 663

    I would dig out about 8-10 inches of soil/clay and put a layer of gravel or stone chippings about 5 inches deep for drainage, then put grit on top of that so you can insert the slabs in it and adjust the level accurately with your spirit level.

  • garjobogarjobo Posts: 85

    thanks for your replies, i will go with the 10inches of clay digging out and hope for the best. Its a large area and will be used a lot.

    Quarry dust i think ive heard mentioned..suspect its the same as gravel? going to expensive, trouble would liked to of done the job properly but my back i dont think can take too much more these days. 

  • Invicta2Invicta2 Posts: 663

    Just  to clarify, when I said grit I didn't mean expensive horticultural grit, but that fine aggregate grit used by builders - much cheaper.

  • LandlubberLandlubber Posts: 396

    Thanks Invicta2: that has also helped me out.image

  • Smiffy3Smiffy3 Posts: 14
    Hi garjobo, we did this about ten years ago, dug out about 4 inches of soil and added a layer of bottoming, or whinstone if you're in Scotland, and laid 3x2 slabs on a bed of dry sand/cement mix. It's right outside of our conservatory and has heavy use, it's hasn't budged in all that time.
  • TopsoiledTopsoiled Posts: 113

    "Chippings to dust" is the aggregate you are after. Use a minimum of 2 inches (4 would be better) and once compacted down (use a whacker plate) it will be pretty solid. You can use mortar to bed the slabs on but this can leach through the slabs and stain them, or bed them on sharp sand. once you have filled in the gaps its not moving. If you use mortar you'll need quite a bit (2inches thick "layer") - do you have a mixer? If not you will regret trying to hand mix that amount of mortar. I'm laying slabs on to very sandy rocky compacted well drained sub soil. I did a 5m x 4m area with sharp sand and the slabs are absolutely solid. Very useful site-


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