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patio falls and layers

Discussion in 'Building' started by zuber ali, 14 Aug 2021.

  1. zuber ali

    zuber ali

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    Hi All

    Looking to lay some slabs down for my new patio and im not too sure on fall lines. when working on fall lines should you calculate from the lowest point you want and work your way back to the highest based on the gradient.

    I would also like to know what would be the best fall line option to use. I have added a image in link below with two potential options, A and B denoted by the red and blue lines.

    I would like to do option B as it seems more simple, but im not sure if the slope would be too great over the full 7m run (i.e at the end of the 7m run my i have grass which would be higher than the patio). in which case option A is better?

    hope this makes sense

    https://ibb.co/RcJWGsT

    Thanks
     
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  3. zuber ali

    zuber ali

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    hi all trying to work out falls and depths for my patio, from my limited knowledge i understand if i have a gradient on my spirit level so that the bubble slightly passes the lines either side, this should be a sufficient fall, i would like to know what fall does this actually convert to i.e 1 in 100, 1 in 60 etc.
     
  4. zuber ali

    zuber ali

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    Hi All,

    laying some porcelain slabs in my garden. I have read its best to first allow for the fall when I'm laying my hardcore, rather than doing this only when i lay the bed as this reduces the amount of material you need to use to make a fall, but this doesn't seem to make sense to me as if the soil layer beneath the hardcore has not been dug out to the correct fall you would end up having thinner layers of hardcore on one end?

    am i correct to assume i should actually get the soil layer first to the correct fall, rather than leaving this flat and adding a fall only to the hardcore/slab layers

    thanks
     
  5. RandomGrinch

    RandomGrinch

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    Find a straight and level surface, lift one end of your spirit level until the bubble hits the line and measure the distance the end of the level is from the ground.
    Divide this distance by the length of your level (in the same units) and you have your fall.
    If there was a standard for these lines, it is probably worth doing this anyway. Many cheap levels I have had, strongly disagree with each other :)
     
  6. foxhole

    foxhole

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    Levels vary. Plenty of mobile phone apps to give you the fall . You can use a line set to fall you require for level.
     
    Last edited: 21 Aug 2021
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  8. cdbe

    cdbe

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    It doesn't matter, you don't lay a patio to fall by levelling individual slabs with a spirit level. You lay them to a line with the fall set using a spirit level set level on a straight edge and a tape measure to measure down.
     
  9. Bonni

    Bonni

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    First step, dig out. Then you need to whack in 3 to 4 inch of hardcore. Then lay down 3 to 4 inch of weak mix concrete. Then full bed porcelain tiles on 3:1 mortar 25mm to 40mm thick. Pick a fall from the house and as long as it falls away, place a string line and bed the tiles.

    So, you need to take the tile thickness, bed thickness, concrete thickness and hardcore thickness into to account to dig out. Even if the fall is 5mm over the entire patio, the water will flow away from the house.
     
  10. JohnD

    JohnD

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    And I'd add, before you start digging, find the DPC.

    your finished height should be two bricks below (or more)

    very often you will find some numbskull has already laid paving that raises the ground above the correct level, so you need to reduce it, to reduce damp problems.

    Have a good look at any drains or gullies while you are digging. If they are in brown-glazed fired clay, they are likely to be cracked and leaking.
     
  11. zuber ali

    zuber ali

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    Oh yeah I should have thought of that. Thanks
     
  12. John D v2.0

    John D v2.0

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    as long as you don't exceed the maximum thickness per layer of hardcore when compacting, you can put in as much as you like within reason to make up the correct levels. You should also dig out any weak spots. e.g. In our drive there were roots from the street tree snaking around underneath, we dug them out and filled in those areas with extra hardcore, so the thicknesses were all over the place 100-250mm, but it didn't cause an issue as it was all well compacted.
    the bedding layer above the hardcore needs to be even thickness, but it sounds that is your plan already.
     
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