Dot Dab Fire resistance

Discussion in 'Plastering and Rendering' started by chapeau, 5 Jan 2010.

  1. chapeau

    chapeau

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    Hi,

    Over on electrics forum there is a question about dropping cables behind dot/dabbed plasterboard from the top.

    I said I thought it was required to put a solid line of adhesive at the top of the board to prevent the spread of fire. Now as what happens a lot, I don't know whether I just made that up, or whether it's actually required.

    Obviously if it is required, no chance of slipping a cable down from the top. So what's the correct answer?

    Cheers
     
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  3. GaryMo

    GaryMo

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    Just to add a little more...... ;)

    Surely the spead of fire should only be between separate fire compartments and not between the downstairs and upstairs of a standard two storey dwelling which is a single fire compartment?

    If there's an internal garage with a room above then the garage is treated as one compartment and the house, including the room above the garage another fire compartment.
     
  4. chapeau

    chapeau

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    Part B of the building regulations (Fire Safety)

     
  5. NickB_99

    NickB_99

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    When using dot/dab, you want a good 'line' of adhesive at the edges of the boards to prevent any movement at the edges which can cause cracks - thisd would include the top edge.
    I would suspect that the spread of fire up the back of wallboard would be a minor effect - the gap is typically only 5mm and wallboard
    has reasonable fire resistance I believe (http://www.british-gypsum.com/pdf/DS-001-03 Gyproc WallBoard.pdf - page 2, fire resistance)

    the quote you provide from building regs seems a bit ambiguous. Would the concealed spaces be more likely cavity wall, stud wall cavity, ducts etc ?
     
  6. trowelmonkey1

    trowelmonkey1

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    personally never heard of this, I can't see how lumps of adhesive will help slow the spread of fire, the boards themselves are rated in minutes for this purpose and the amount of required fire resistance that you need to achieve to meet regs etc would be done by using the appropriate type of board or even 2 skins of board.

    that's just how i understand it of course.
     
  7. chapeau

    chapeau

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    Well perhaps it's just an anal way of reading the regs. Well, it was brought up on the electric forum, would you expect anything else :)

    The reg says fire and smoke and if you read the approved document it doesn't have a minimum sized hole and implies that any space should be sealed. The part of the reg I quoted appears to apply within a fire compartment, other sections specifically mention compartments, the one I quoted doesn't.

    When I have hacked up some dot and dab in me own gaff have always put adhesive across the whole top as it stops draughts coming out of the socket holes, and I assume this also improves the effective insulation properties of the wall as no constantly replaced cold air found just behind the board.

    Cheers for comments
     
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