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Some structural screed questions

  • 02-01-2013 11:31pm
    #1
    heavydawson
    Registered Users, Registered Users 2 Posts: 1,210 ✭✭✭


    Hey all,
    New build underway and just looking for some pointers on structural screed.
    We've engaged a precast slab provider who are providing a 150mm slab that requires a 75mm structural screed. So I've got two questions:

    1. Is structural screed any different to your standard 25N concrete?
    2. How soon after the slabs are in place does the screed need to be pumped in? Do we just take the block work up a couple of courses then pour?, or do we finish all blockwork, get the roof on, have the plumber come back and do the necessary work for the rads upstairs, then pour?

    I appreciate the mods are pretty strict on the discussion of structural issues, but I think (hope) this is a generic enough question on the order of things rather than a genuine structural question
    Thanks in advance!
    Tagged:


Comments

  • #2
    muffler
    Registered Users, Registered Users 2 Posts: 46,555 ✭✭✭✭muffler


    heavydawson wrote: »
    I appreciate the mods are pretty strict on the discussion of structural issues, but I think (hope) this is a generic enough question on the order of things rather than a genuine structural question
    Yup! Careful with the replies folks. Thanks.


  • #3
    archtech
    Registered Users, Registered Users 2 Posts: 1,046 ✭✭✭archtech


    First question who's signing off on certification of the completed works and have you asked them?

    Did you ask the floor supplier for their opinion. Very often they have specific requirements as to the screed. In many instances the next course of block work is built off the screed.

    All of the above should give you guidance as to where you will find your answer.


  • #4
    heavydawson
    Registered Users, Registered Users 2 Posts: 1,210 ✭✭✭heavydawson


    archtech wrote: »
    First question who's signing off on certification of the completed works and have you asked them?

    Did you ask the floor supplier for their opinion. Very often they have specific requirements as to the screed. In many instances the next course of block work is built off the screed.

    All of the above should give you guidance as to where you will find your answer.

    Hey archtech,
    My engineer will be signing off. I'll talk to the floor supplier and the engineer tomorrow morning and will post back here with whatever answers I get.


  • #5
    A fella called fish
    Banned (with Prison Access) Posts: 188 ✭✭A fella called fish


    A structural topping is provided to ensure overall lateral stability by causing all flooring units to act as a single rigid diaphragm, it also forms a bond with the units to ensure a composite section which increases the floors moment capacity.

    Mesh is usually provided within the topping to provide resistance to shrinkage cracking and also to satisfy the peripheral tying requirements where applicable.

    As you can see, it's an important part of the structure and with that in mind I suggest you take project specific advice from the Project's Structural Engineer, not from strangers on the internet (myself included). I don't wish to sound blunt, but it's for obvious safety reasons that I'm suggesting this.

    Also, be aware that some long span units require slabs to be propped prior to pouring the screed.


  • #6
    AnarchistKen
    Registered Users, Registered Users 2 Posts: 129 ✭✭AnarchistKen


    Also another key point is that an edge shutter will have to be installed around perimeter of pour.

    Putting up blockwork to act as a shutter will not work as the blockwork has to begin it's first course on top of the structural screed.

    Good point about backpropping. As always consult with flooring supplier they can advise if units need propping or not.


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  • #7
    heavydawson
    Registered Users, Registered Users 2 Posts: 1,210 ✭✭✭heavydawson


    Thanks for the pointers all.
    So having talked with a variety of parties involved, it seems the following is the case:
    1. Slabs put in place and props added underneath (props sourced already)
    2. Single perimeter course of 3" soap put in place on inner leaf above slab
    3. Expansion joint put in place on inside of soap
    4. A142 mesh placed
    5. Upstairs pipework put in place and possibly tied to mesh
    6. Stairwell cavity to be shuttered to a height in line with the 3" soap on on the internal leaf
    7. Screed poured and allowed to dry
    8. Blockwork continued on outer course above 3" soap, and internal blockwork commenced on top of screed.

    Also FWIW, I was told a standard 30N10 sand/cement mix would suffice for the screed (to a depth of 75mm as specified previously). We don't have UFH, so heat release speed from the floor is not a consideration (some of the sub-75mm screeds would have been used for this scenario from what I've looked into).


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