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T-Beam Flooring - Screed Options

  • 30-03-2016 11:58pm
    #1
    Registered Users, Registered Users 2 Posts: 623 ✭✭✭


    Appreciate this may seem like a structural query, but it's not really - I'm trying to identify my options.

    So, a portion of our house has a suspended floor (over basement) using T Beams with polystyrene in-fill as opposed to block. Seems like a good job and am happy with it, but I was planning to put an extra 50mm insulation on top, then 50-60mm of screed and then tiling.

    However, one of the floor screed vendors and my BER assessor both question if such a thin screed would suffice over the insulation in-fill. I'm getting bounced around a little over and back between the T Beam vendor and the screed vendor as to who's product would be handling any point loads, where the structural integrity comes from, etc.

    I'm sure that structurally it would be sound enough, but my main concern is any movement as we are putting in large format marble tiles and I don't want them to crack.

    So my questions are;
    1. What screed products would people recommend when it comes best overall strength?
    2. What would be the minimum thickness of said products to ensure as little movement as possible?
    3. Presumably the use of mesh would help reduce the thickness required?

    I'd like to pack in as much additional insulation as possible, but am willing to go with the full 100mm of screed if needs be. I'd also prefer one of the liquid/self levelling products if possible.

    I will be running this by my engineer prior to doing anything further.


Comments

  • Closed Accounts Posts: 748 ✭✭✭Johnnyhpipe


    Hi, Talk to the engineer. He might need structural screed for either composite action (strength) or diaphragm action (stability). You will get wrong/varying advice on here since no one has full knowledge of your specific job.


  • Registered Users, Registered Users 2 Posts: 623 ✭✭✭tedimc


    Thanks Johnny.

    I've been going around in circles a little on this. Ultimately, the screed won't be structural as it is insulated from the beams (insulation covers the top of the beam by 20mm to stop cold bridging). And even at 40 to 50mm most of the liquid screed type options will be sufficient, but I'm not getting any guarantees about cracks.

    In the interest of anyone else who has a similar issue; after talking to a few people, my latest thinking is to go with 75mm of 6 to 10mm chip concrete and maybe put some mesh in it. Probably overkill strength wise, but its the safest option to prevent tiles cracking. The only problem is it won't be as level/smooth as some of the liquid screeds, which is unfortunate.


  • Registered Users, Registered Users 2 Posts: 21,808 ✭✭✭✭Water John


    I think Ted, some of the readymix suppliers have an additive they can put in which they use on screeds for UFH. That should help with the levelling.


  • Registered Users, Registered Users 2 Posts: 12,889 ✭✭✭✭Calahonda52


    OP:
    Am assuming the T beam is actually inverted, with the wider piece below.

    is this a DIY design to put poly between the beams as opposed to block?
    In the absence of block, which performs like bridging in a timber floor, and no connection between the top screed and the T beam, what is going to stop the beams flexing laterally?

    you need to reflect on how the floor will work from a structural point of view and also on your expectations of mesh in the screed.
    So what will stop the T beams flexing?

    The loading, the depth of the T beam, the beam spacing and the bottom reinforcement in the beams.

    However, once you come up beyond, for simplicity, the centre of the beam, all the material is is compression, something concrete is very good at and the mesh will add little or no structural value to the floor flexing, it may help with the screed not cracking, but with the cold bridge break, then they are two different structures and need to be designed as such.
    Finally the poly will reduce the sound proofing big time..

    “I can’t pay my staff or mortgage with instagram likes”.



  • Registered Users, Registered Users 2 Posts: 623 ✭✭✭tedimc


    Hi Calahonda52,

    Not a DIY job - it's a proprietary system (I believe) provided by a concrete company in Co.Wicklow. Yes - T beam is inverted with the lip supporting the polystyrene block

    The polystyrene is high density, so it tends to keep the beams equal distance apart - similar to timber bridging. According to the manufacturer numbers, the poly blocks with 70mm of screed has actually a stronger load bearing than block.

    Even if the mesh only helped with the cracking, this would be worth it as it may prevent he cracks coming on up through the tiles. Not too worried about sound as this is over a basement - thermal insulation is my main worry, but worst case scenario I will insulate from below.


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