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Strengthening suspended floor for large tiles, advice please on idea

Discussion in 'Tiling' started by happyhero, 27 Aug 2020.

  1. happyhero

    happyhero

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    I want to run large tiles from concrete floor to suspended timber floor without using an expansion joint.

    To explain the layout first we have a house with an existing single storey extension across the width of the back of the house, which is about 5.5m wide internally and 3.8m deep towards the back garden. Standing in the extension facing into the rest of the house with your back to the back garden, the kitchen is on the left side and the lounge on the right. The kitchen has units both sides and is 3m long with about 1.3m between the units. So if you walked out of the extension into the kitchen you would walk between the units through the kitchen into the rest of the house. Hope that all makes sense.

    I have bought 600mm x 900mm x 10mm porcelain tiles but in the actual extension we wanted a heated floor so I also bought 10mm insulation backerboards, a Warmup DPM plastic self-adhesive mat and loose heating cable.

    The self-adhesive mat does 2 jobs it contains the cable when laid and allows the tile some movement (you can buy this sort of sheet for non-heated floor to allow for movement/expansion/contraction etc it was explained to me). What I am getting at is it is good to have under the tiles even if you don’t have a heated floor. Several stores wanted to sell us this type of mat regardless of a heated floor we eventually chose to add.

    I want to run the tiles all through the concrete floor extension and into the timber floor kitchen and so normally you would need an expansion joint but I would like to avoid an expansion joint and have consulted some tilers in one store as to how I could do this. They said ideally you fit an expansion joint but if you want to avoid it you must do a lot of work to try and make the suspended wooden floor in the kitchen as strong and rigid as possible. They said the insulation board and plastic sheet will help disconnect the tiles from the timber floor.

    So I was thinking how to make my timber floor rigid. It has a gap under the joist of about 250mm(10in). I had this idea so tell me what you think about it and if you think it will work. I was going to get some plastic pipe, 4” diameter or maybe better 6”. Clean the area of rubble under the joist and cut the pipe to fit tight between the joist and the cleaned area below which seems to be concrete. Then I would put some rebar down into the pipe the same length as the pipe and pour concrete into this pipe. I also thought to stop bounce I would drill the top of the joist over the pipe and put a recessed screw or bolt to go into the concrete thus securing the joist to the concrete post I make. I was thinking of making these posts every 18” or 24” maybe, its fairly easy to do and it seems a strong idea to me plus with the 10mm backerboards and plastic movement sheet I think that would do it, what do you think?

    Can this work?

    Any feedback appreciated.
     
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  3. Lower

    Lower

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    You need to stiffen up the floor as well as the joists so that the floor itself doesn't flex between the joists.

    Normal way to do this is to lift the existing floor, put loads of noggins between the joists and then put 25mm ply down as the floor itself.

    This ties the whole floor/joist assembly together as a single piece and makes it very stiff and stable.
     
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  4. happyhero

    happyhero

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    Yes forgot to mention the noggins, I was going to do that too, they recommended it too. I was thinking of replacing the old floorboards with plywood so as you advise it I think that is what I will do, thanks for the tips.
     
  5. Lower

    Lower

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    If you think you need to provide support for the joists themselves, i'd build brick piers with a reasonable foundation and then pack the piers to the bottom of the joists.

    But as long as the joists are decent size, once you noggin them all together and put a thick layer of ply on top, you'll make a very stiff floor.

    The make sure you use flexible tile adhesive and grout.
     
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  6. happyhero

    happyhero

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    I was just thinking does the ply need to be marine ply or will decent ordinary ply work?
     
  7. Lower

    Lower

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    The appropriate ply used to be called WBP ply. No idea what its called now. Marine ply is a grade or two up from WBP ply.
     
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