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Thread: Advice on filling a big hole in workshop floor

  1. #1
    Engineer Kernow64's Avatar
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    Default Advice on filling a big hole in workshop floor

    Hi All,

    I'd be grateful for some advice on filling a big hole in the floor of a barn which will become my workshop - and sadly it is not suitable for being turned into an inspection pit.

    The hole in in question is what I assume is an old sheep dipping trough, dug into the floor. It is/was galvanised and is about 8'6" long x 2'6" wide by 3'6" deep for half the length then sloping up like a swimming pool. No other use for it and I have neither the means nor appetite for digging it up so I am planning on filling it in as a first step towards levelling the floor which is uneven concrete and rocks.

    I have a 110 load of bricks, broken concrete and other rubble courtesy of the local Freecycle group waiting to to go into the hole and a small cement mixer arriving later in the week but I've never filled a hole this deep.

    The area where the hole is will not be driven over and will just be for storage and walking over.

    How much compacting/tamping will I need to do and should I be including layers of concrete in between the layers of rubble?

    When I get onto levelling the floors, I would like to include a damp proof membrane. Is there a minimum thickness of concrete to go on top of the membrane - the old floor is very uneven and in some places only an inch or so is needed to level things off and I don't want to put a membrane down if it will compromise the the strength of the floor.

    As ever, any thoughts would be very welcome.

    Cheers!

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    Engineer phoenixdave's Avatar
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    Default Re: Advice on filling a big hole in workshop floor

    I would try to get the metal out first if possible, rusting steel is very good at cracking concrete. If you fill the hole with rubble crushed reasonably small it shouldn't need much compacting, though will need a few 110 loads to fill it! No need for layers of concrete between layers of rubble.

    I would make sure I had at least a couple of inches thick concrete everywhere, thinner concrete is very prone to breaking up. Can't help re the Damp Proof Membrane, I think they usually put a layer of sand in, which would increase your thickness even further. Hope this is some help. David
    1982 ex-mil 109 2 1/4 petrol on lpg series III, 'Phoenix'

    1983 2 1/4 diesel 88" series III, 'Willy', currently in bits.

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    Consultant Richie_asg1's Avatar
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    Default Re: Advice on filling a big hole in workshop floor

    There is a danger of what you put in there sinking, then leaving a void under the thin layer of concrete, and cracking it if something heavy was pushing on it - such as an axle stand supporting a vehicle you are under.

    If the metal wants to come out then take it out, otherwise knock and fold it in so you can get a good 4" concrete over the area. If you can add 2" weldmesh in the concrete there should be no danger of it sinking or popping through. Add soil as you go with the hardcore and pack it down as best you can so it doesn't have any room to sink.

    I would still want to make it into extra storage or a pit, water tank or compressor tank storage or part of a heat store, and just use steel treadplate on beams over it.

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    Engineer Kernow64's Avatar
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    Default Re: Advice on filling a big hole in workshop floor

    Thanks for thoughts guys.

    Having looked again at the tough, the galvanising on the inside is pretty good (its a bit rougher on the outside where it is contact with the ground) and I really don't have the appetite for digging it out and nothing to do with it even if I could get it out in one piece so I'll have to take my chances on it rusting in the future.

    I did think about using it as storage but would find the flat area more use. Its on a different level from the bit where I would be working on vehicles so no danger of an axle stand sinking - that area has large flagstones which have probably been there for centuries.

    I'll compact it all as best I can, reinforce it with mesh and put a thick layer of concrete on top.

    Getting quite excited, I've never had anywhere decent as a workshop before, let alone one I can get a 110 into so quite prepared to put a bit of effort in.

    I'll be interested to see what the load of rubble I have looks like when compacted - there was plenty more where it came from so another trip or two may be needed.

    Cheers!

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    Disco 1 TDi specialist zollaf's Avatar
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    Default Re: Advice on filling a big hole in workshop floor

    i would put some sand in it then rubble, sand etc,...... so there are less air gaps, then whackker it down.. you want the concrete overlapping, not just the same sixze as the hole so it can sink into it. 6'' of concrete overlapping 6'' on the sides, then if it does settle the concrete wont budge. job done.
    currently between landrovers, just a scabby old audi with 359,000 miles under it.

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    Engineer Kernow64's Avatar
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    Default Re: Advice on filling a big hole in workshop floor

    Thanks all.

    Spent a few happy hours today throwing sand and rubble into my unwanted sheep dipping trough and smashing up the bricks with a sledge hammer so it is pretty compacted.

    A 110 load (a 110 with 130 HD suspension that is ) has roughly half filled the trough and I'm off to collect another load (and a new face mask!) tomorrow.

    Horrible job but looking forward to the end result.

    when the rouble is level with the sides of the trough, I'll start levelling the rest of the floor so that the whole area gets covered. I've found quite a lot of galvanised fencing wire which should help reinforce the concrete over the trough and any other areas I've had to fill in.

    Thanks again for tips and reassurance.

    Cheers.

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    Engineer bananahead's Avatar
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    Default Re: Advice on filling a big hole in workshop floor

    Throw the rubble in and aim for four inch of concrete. If the hole is surrounded by concrete, use dowel bars. This means drilling holes every 500mm about 60mm below finished floor level (in this case) into the surrounding concrete horizontally and insert metal bars. The bars should be probably 20mm diameter to be trafficable but obviously you're not driving on it.. Do that to tie the new concrete to the old, a sheet of light gauge reinforcement mesh and despite what happens underneath your new concrete it shouldn't crack or sink. If you do as I've described, and use a compaction plate (Wacker) you could drive a truck over it no problem. Use 250-300mm of concrete and you've pretty much done what happens in factory yards. I know because it's what I do for a living..

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    Default Re: Advice on filling a big hole in workshop floor

    Quote Originally Posted by bananahead View Post
    Throw the rubble in and aim for four inch of concrete.

    ....

    I know because it's what I do for a living..
    Thanks for that extra advice - pretty much what I ended up doing except that I just used some 6" galvanised masonry nails to tie the new concrete to the old.

    Ran out of materials but hope to finish tomorrow.

    Cheers.

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    Default Re: Advice on filling a big hole in workshop floor

    did you have to borrow thors hammer to drive 20mm thick masonry nails in ?
    Drives: 1982 series 3 88" station wagon

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    Default Re: Advice on filling a big hole in workshop floor

    Quote Originally Posted by DarrenH View Post
    did you have to borrow thors hammer to drive 20mm thick masonry nails in ?
    No, I just used Occam's razor to trim them down a bit!

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