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  • #1822409
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    alexv
    Participant
    Joined: 27 Feb 2011
    Location: Chongqing, China + 87 Northern Haute Vienne in the summer
    Total posts: 97

    I want to make a nice concrete floor for my 5x10m ground floor garage. My house is a 70 year-old stone building built into the hill, with no foundations. The garage floor is currently a dirt floor. Some parts have bare rock a few inches down.

    I would like to get a professional to oversee a concrete pour, as I am not experienced enough to do it myself, and you can’t make mistakes with this sort of thing. I can do much of the preparation and formwork myself.

    Does anyone have any advice about how to do this or thoughts about the advisability of doing it at all? At the moment, the fact that air is allowed to circulate around this cavernous space below the main house mitigates against some of the moisture wicking its way up the walls to the main house above, along with the floor draining water into the ground. At the same time, I would like it to be a useable space and protect myself from possible radon poisoning. Do I leave space around the edge to allow for drainage? Do I put plastic sheeting under the concrete?

    Thoughts?

     


    #1822448
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    thw8s
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    Joined: 08 Dec 2012
    Location: 49
    Total posts: 215

    As a chartered civil engineer who specialised in concrete technology for their final year university degree thesis perhaps I can offer some ‘expert’ advice. I mention this as I have just been reading about the value of getting/having a degree.

     

    First, you do not ‘pour’ concrete – it is ‘placed’!

    Plastic sheeting may help unwanted debri contaminating the concrete during placing.

    What stops damp climbing your walls now? Why will concrete make this worse? Not something I would worry too much about.

     

    Perhaps there are alternatives – gravel? Probably much cheaper and easier to ‘place’

    Paving slabs?

    Generally if a ‘readymix’ truck can get easy access concrete is fairly easy to place for 2 fairly fit people, especially as formwork will be more difficult usually and you said you can handle this.

     

    Hope this helps


    thw8s

    #1822477
    mysty2
    mysty2
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    Joined: 29 Jul 2012
    Location: N/A
    Total posts: 9603

    RE radon poisoning.

    According to a notaire we use in the Cantal dep 15, just open a window once a week to air the house and there will be no issues with radon.


    #1822497
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    fittersmate
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    Joined: 08 Jun 2009
    Location: Brittany France dept 56
    Total posts: 1624

    I had a 15 metre x 10 metre concrete slab x 100 mm thick in our large barn poured by a registered insured contractor a year or two back.

    From what I saw him and his crew do, and from talking to him, here are my observations or experience of what they did.

    The barn floor was dirt with rocks evident here and there, I know there were rocks evident there because I kept tripping over them! :negative:

    1 – Dug the base out with a mini digger to get rid of the loose material which was a mix of wood sawdust, dirt and rocks, it had been a sawmill/woodwork machine shop for 50 years, underneath was virtually solid rock.

    2 – Level with the digger as much as possible and compact the loose material with a wacker plate.

    3 – Blind with 0/30 crushed granite and build up to the level required, thouroughly compacted with a wacker plate.

    4 – Fit formwork around the perimeter to retain the concrete.

    5 –  Lay polythene waterproof membrane and tape the joins, take the polythene up about 150 mm above the eventual top level of the slab.

    I was told that the main purpose of laying a membrane under the concrete, apart from the obvious reason of stopping damp coming up through it, is to stop the concrete drying out before it has cured.

    6 – Lay out steel reinforcing mesh, raised up above the polythene by about 40 mm with plastic spacers – you need the mesh in the concrete not underneath it.

    7 – And then, the day the concrete got delivered, this is where you need to have someone there who is used to ordering the concrete from a supplier that they know and can rely on to supply the correct mix.

    8 – The truck with a tapis (conveyor) turned up and proceeded to wreck our front garden to get into postion to poke the tapis through the barn window(we had removed the window frame and glass complete)

    9 – The concrete was delivered at speed from the truck, the crew of three had another three helpers, so six in total spreading, barrowing and raking it level, they were in wellies walking about in it, a very wet sloppy self-levelling mix.

    10 – They then tamped it and that was it, no floating off needed

    11 – I kept vehicles and anything heavy off it for four weeks, and sprayed it with a hose regularly to help it to cure – probably being a bit over cautious there.

    This was done in November and it’s been fine, no movement, no cracking and have had heavy vehicles and machinery on it ever since.

     


    • This reply was modified 12 Feb 2018 21:28 by  fittersmate.
    #1822513
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    Chanceux
    Participant
    Joined: 17 Mar 2010
    Location: Picardie
    Total posts: 13130

    For caves and sous sols I find that block paving is a great solution, it can be done bit by bit, materials can be carried down as required, no access needed for a cement pour, the finished job is breathable in that moisture can still come up and fluids can drain through it, it can be lifted in sections for future work, passing gaines, waste pipes etc.

    It also looks the part and costs a lot less than concrete.

    I would do my cave but the floor has already been lowered so far that it undermines the bottom of the walls of the building (no foundations) and I dare not excavate more even though the finished job would add strength.


    #1822515
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    alexv
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    Joined: 27 Feb 2011
    Location: Chongqing, China + 87 Northern Haute Vienne in the summer
    Total posts: 97

    Thanks all for the replies. The reason I mention moisture going up the walls is that sometimes I see mushrooms growing out of the mortar up to half way up the 3 metre high walls. And I assume that what stops it going any higher is the fact that the big draughty barn doors, the empty space and the dirt floor help the place to be adequately ventilated and drained.

    I want the place to be a multifunctional work/play space, so gravel wouldn’t really work as a surface, but block paving would be OK. I had considered that before and it would certainly be less daunting a job.

     


    #1822518
    DominicBest
    DominicBest
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    Joined: 14 Aug 2015
    Location: Poitou Charentes
    Total posts: 2500

    Fittersmate, Chancer and Kevin from Grand Designs all talk about pouring concrete so I think it probably is an accepted term.
    Be careful about any slope on the floor. There was a post either here or on AI by someone who had had a concrete floor put in his garage with a slight downhill gradient from the door to the back wall. Any significant rain falling on his drive resulted in a lake that was difficult to get rid of in an area he’d hoped would be dry.


    #1822520
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    snoteezyizit
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    Joined: 04 Sep 2014
    Location: N/A
    Total posts: 15

    Be aware of the need for accuracy in levelling the area at the base of any garage door. There is potential for creating gaps which can let in the weather and rodents. Much better get it right before it dries than resort to bodging with strips of rubber etc later. Good luck!


    #1822559
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    mikej
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    Joined: 21 Jun 2011
    Location: Dordogne sometimes and Kent the rest
    Total posts: 5287

    Do consider a sharp sand levelled compacted base and block or paving slabs, no membrane underneath it, not needed and would be detrimental to any moisture dispersal, do put some kind of roll over at the door.

    Mike


    WFIPFLL

    • This reply was modified 13 Feb 2018 12:32 by  mikej.
    #1822566
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    Chanceux
    Participant
    Joined: 17 Mar 2010
    Location: Picardie
    Total posts: 13130

    Agreed Mike, I have done a sous sol for someone else and it continues to breathe as well as it ever did, in another area where they had concreted there is now a huge damp problem which was not there before.

    My cave is well ventilated and seemingly dry but a cardboard box laid directly on the floor will decompose in a matter of days.


    #1822624
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    fittersmate
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    Joined: 08 Jun 2009
    Location: Brittany France dept 56
    Total posts: 1624

    Agreed Mike, I have done a sous sol for someone else and it continues to breathe as well as it ever did, in another area where they had concreted there is now a huge damp problem which was not there before. My cave is well ventilated and seemingly dry but a cardboard box laid directly on the floor will decompose in a matter of days.

    <hr />

    I confirm that since I had a proper concrete floor installed in my barn, I do not have a problem with my cardboard boxes decomposing.


    #1822639
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    Chanceux
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    Joined: 17 Mar 2010
    Location: Picardie
    Total posts: 13130

    Yes but if I had a concrete floor in my cave it would become a paddling pool unless the walls (and beneath the concrete) were tanked :cry:


    #1822647
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    mikej
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    Joined: 21 Jun 2011
    Location: Dordogne sometimes and Kent the rest
    Total posts: 5287

    fittersmate

    What gives away a potential problem is the OP’s first post “My house is a 70 year-old stone building built into the hill” therefore the outside ground is above floor level.

    Mike


    WFIPFLL

    • This reply was modified 13 Feb 2018 22:15 by  mikej.
    #1822653
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    alexv
    Participant
    Joined: 27 Feb 2011
    Location: Chongqing, China + 87 Northern Haute Vienne in the summer
    Total posts: 97

    Thank everyone. I am leaning towards the paving option. I have my own little quarry with granite-y sand. I could maybe compact that on the floor. I have the experience of decomposed cardboard, and prematurely gone-off cement, so it can get pretty damp down there (though not flooded). The house has 3 storeys. It has a small footprint, 50 square metres, same as the garage itself. The garage is at the road level and is roughly half in the hill. The living area is on the 1st floor and roof. Damp is just a fact of life, and it is uneconomic to remove the bare rock from the back and sides of the house.

    Just a question: what is a rollover? At the moment there is a 70cm-ish x 5 metre  concrete apron at the entrance, which the large corrugated metal and wood doors sit on. Water never comes in as there is a scooped channel outside sloping down from the door, which channels any torrents away. Eventually, I would like to replace the doors with some sliding folding doors like this: https://www.reynaers.fr/fr-FR/products/cf-77


    #1822709
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    mikej
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    Joined: 21 Jun 2011
    Location: Dordogne sometimes and Kent the rest
    Total posts: 5287

    Anything sloping down from the door threshold is a rollover, just means the entrance slopes up to floor inside, so any acumalated water outside drains away from the entrace.

    The reason for using sharp sand is because it drains, ordinary building sand just turns to a pudding like consistancy and will not drain as efficiently.

    Mike


    WFIPFLL

    • This reply was modified 14 Feb 2018 14:26 by  mikej.
French Electrical & Other Building Issues
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