Plasterboard /dab/fixings

cosmowillie53

I hope to have some 62.5mm insulated plastered put up shortly (by a plasterer).
They will be going onto some old walls. Plasterer will using some sort of adhesive (bonding compound) and dabbing them on.

Q: Should they also be kept in place with long metal fixings.

Thanks.

aujopimur

Dabbing is fine as long as the existing surface is ok, if it's loose or flaky you could have problems.

dathi

all slabs should have a continuous line of adhesive around the edges of slabs to prevent air circulating behind slabs and they should also be mechanically fixed to the wall

TheLastMohican

dathi wrote: »

all slabs should have a continuous line of adhesive around the edges of slabs to prevent air circulating behind slabs and they should also be mechanically fixed to the wall

Just one question: how could air circulate behind the boards if the are mushroomed onto the wall?

650gs

good one alright

wayoutwest

TheLastMohican wrote: »

Just one question: how could air circulate behind the boards if the are mushroomed onto the wall?

There will be an airgap of about 18mm -ie: the thickness of the adhesive. Further mechanical fixings won't reduce this gap.
Continuous line of adhesive around edges of slabs [and around electric switch/socket boxes], is to trap the air. As well as increasing the airtightness of the slab, this also prevents drafts from entering into up into any surrounding ceiling/attic voids [further heat loss as well as fire risk].

dathi

http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,18756,en.pdf sorry was away for weekend there is the accredited detail from the department of environment on how to fix slabs

L1979

TheLastMohican wrote: »

Just one question: how could air circulate behind the boards if the are mushroomed onto the wall?

There are different u-values for an insulated slab depending on the fixing technique used. Dot and dab would have a better u-value if you create a vacuum between the slab and the wall, by using a continuous line of adhesive, as discribed above.

If you use dot and dab, you are required to use metal fixings to meet fire reg's. Similarly if you use plastic fittings, you will have to use some metal fittings too.

wayoutwest

The metal fixings are to keep the board from falling off the wall in the case of a fire and therefore reducing the spread of damage to rooms/attics above. Does anyone know the correct amount of metal fixings [per 8x4 slab] that are required, in order to comply with building regs?

L1979

wayoutwest wrote: »

. Does anyone know the correct amount of metal fixings [per 8x4 slab] that are required, in order to comply with building regs?

3, placed in center of board

TheLastMohican

You need 12. Every 2' along the 8' edges and along the centre. You may get away with combining at the edges - one mushroom to cover both boards.

wayoutwest

So what's it to be then.......three in the middle or twelve at 2' centres?

TheLastMohican

wayoutwest wrote: »

So what's it to be then.......three in the middle or twelve at 2' centres?

If you're blobbing the boards you can drill a few mushrooms after the adhesive sets. If you are fixing with mushrooms only, you need a fixing every 2'.

TheLastMohican

TheLastMohican wrote: »

Just one question: how could air circulate behind the boards if the are mushroomed onto the wall?

I thought you were fixing with mushrooms only, ie tight against the wall

wayoutwest wrote: »

There will be an airgap of about 18mm -ie: the thickness of the adhesive. Further mechanical fixings won't reduce this gap.
Continuous line of adhesive around edges of slabs [and around electric switch/socket boxes], is to trap the air. As well as increasing the airtightness of the slab, this also prevents drafts from entering into up into any surrounding ceiling/attic voids [further heat loss as well as fire risk].

Correct. The mechanical fixings to be fitted only after the adhesive goes off.

Leiva

Do you always have to use plasterers compound (adhesive) or can you just mushroom directly onto the existing wall?

or is the adhesive there to create a void for air circulation or mould or something?