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Insulated plasterboard

  • 12-05-2022 9:29pm
    Registered Users Posts: 58 ✭✭

    Hi All,

    I already have 37mm insulated plasterboard already on my walls, wondering would it be possible to add 100mm insulated plasterboard ontop of that to beef it up or would there be an issue with that? Cavity block wall 1950s bungalow. Thanks


  • Registered Users Posts: 757 ✭✭✭C. Eastwood

    60 mm of a good insulation in total will give you a U value of approx 0.3 watts/m2/degreeC/hr. Adding an extra 40 mm insulation would do. Fix with Metal Mushrooms Insulation fixings. These will be a cold bridge, and may cause black mould to grow on the plaster skim at each of the heads. To prevent this cold bridge coat the new plasterboard slabs with undercoat first and then the 3mm plaster skim.

  • Registered Users Posts: 583 ✭✭✭SC024

  • Registered Users Posts: 757 ✭✭✭C. Eastwood


    Undercoat. - If you wish.

    Using metal mushroom fixings in a cavity block wall will be a Cold Bridge.

    See photos:-

    Because of the hollow cavity blocks wall which have a U value of 2.1 watts/m2/degreeC/hr, - cold from the block will make the heads of the fixings cold and condensation mould growth will form on the 3mm plaster skim over each fixing.

    This is not a big problem. It can be wiped off with a damp cloth.

    To prevent this from occurring- the slabs are coated and straighten with 10 mm of Bonding Coat Undercoat plaster. + 3 mm skim.


    Bear in mind that the OP is fixing new insulated slabs on over existing insulated slabs, and the new slab surfaces may not be straight.

  • Registered Users Posts: 58 ✭✭Davidwhit1

    Thanks for all that valuable information C. Eastwood.

    I should probably take off the existing window reveal plasterboard and reslab that too?

  • Registered Users Posts: 247 ✭✭hayse

    Demolish, 1950’s bungalow where are you going. Putting good money into bad.

    Halt the Dermot Bannon binge viewings.

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  • Registered Users Posts: 757 ✭✭✭C. Eastwood

    Your welcome Davidwhit1.

    if the existing window reveals are plasterboard slabs- yes I would remove them and apply new plasterboard slabs with insulation- even 10mm, or more depending on the amount you can fit in relation to the windows frame thickness.

    Then you can fit a plaster corner bead and skim the entire wall and reveals.

  • Registered Users Posts: 1,231 ✭✭✭monseiur

    Not hijacking the thread, but I was just wondering would the cavity block be strong enough to hold these metal fixings. (Assuming cavity block in this instance is what I call 'hollow block')

  • Registered Users Posts: 757 ✭✭✭C. Eastwood


    Your not a hijacker :-D

    Yes. Cavity blocks are perfect for IWI, with insulated slabs fixed with mushroom fixings.

    Cavity blocks (hollow blocks) are the same concrete as standard concrete blocks. Both are made with a crunching strength of 5 N/mm sq.

    Cavity blocks are still used for construction in parts of Dublin and are approved by Homebond. All the details are given in the Homebond House Building Manual.