concrete ceiling

Wig

I am wanting to help my friend who cannot afford to pay a builder.

the job has been started but the builder has not returned for a year...

anyway...

There is a room on the ground floor, it is to the side of the house and links to the kitchen through an internal door. this part of the house is single storey with a flat roof. The roof is solid concrete which must be about 4 - 6 inches thick. on the ceiling in this room the ceiling is bare concrete and there are some conduits carrying electrical wires.

I am thinking of suggesting that we put up some insulated plaster board dot and dab it onto the cieling. something like 25mm foam.

I know this board can be dot and dabbed onto a wall, question is can it be dot and dabbed to a ceiling? or would it need to be screwed? Given that it is solid concrete what is the best way to do it?

thanks

phil24_7

Dot and dab would be a right pain, even the muck went off quick enough. Mechanical fixing would be a lot better and easer so long as the roof can take it.

How was the concrete formed/fixed? Pre cast as 1 piece, pre cast in multiple pieces or formed in situe or is it black and beam style?

If possible it would be easier to fix treated roofing battern to the roof then screw plasterboard to this. I have just done similar to a block and beam floor. I attached treated CLS timber to the blocks, travelling in the same direction as the concrete beams (can't drill the beams as it reduces their load carrying abilities), the counter battened with roofing batten before boarding. The CLS was fixed to the block with some concrete screws to avoid the need for pilot drilling, removing the CLS, re-drilling, pluging then screwing!

MisterBaxter

I would say that the sheets are too large and too heavy to rely solely on dot and dab for ceiling. Also how are you going to get around the conduits, presumable cutting a channel?

phil24_7

It might be worth spacing the board away from the concrete so that your mate could fit down lighters should he wish.

Furts

My thoughts are the same. It will be hard going to drill if it is pre-stressed concrete, and strictly speaking you should not. But I doubt you will suffer any damage by doing so - not too many fixings will be required. If you want to chance it products like Sticks Like will probably cope with the weight- but run this past the manufacturer first. (I think this is Evo Stik). By this I mean the battens and not the foam backed boards!

There is an advantage with this method. You can put insulation like fibreglass/Rockwool to insulate the ceiling. This will be cheaper than foam backed plasterboards - which are relatively expensive. Make sure you fit a vapour membrane when doing this or your good works are likely to face ruin - possibly in a short time!

phil24_7

For better insulation you could just form a false ceiling 150 or 250mm down from the current ceiling. Allow a 50mm gap at the top and then fill the void/gaps between joists with 100mm PIR board or 200mm of normal roof insulation.

Wig

Looks like it is pre-cast in one piece

How thick would the battens need to be, to screw the plaster board into?

Re the conduits, was thinking of cutting channels into the foam. But if battens are used, the battens would be thick enough to make this unnecessary the conduit is about 20 - 25mm thick.

Wig

Furts wrote: »

By this I mean the battens and not the foam backed boards!

Right, I was wondering if you meant the boards :beer:

There is an advantage with this method. You can put insulation like fibreglass/Rockwool to insulate the ceiling. This will be cheaper than foam backed plasterboards - which are relatively expensive. Make sure you fit a vapour membrane when doing this or your good works are likely to face ruin - possibly in a short time!

Vapour membrane .. where and why?

phil24_7

Roof battens are 25mm thick and are dirt cheap from builders merchants. The vapour barrier goes on the warm side (so below the insulation).

phil24_7

Water vapour can reduce the effectiveness of the insulation, rot the timbers and damage the structure of the roof by holding water against it permanently!

If not insulation then there is no point!

Wig

wonder if I could screw joist hangers onto the walls and have joists hanging on the walls the max span is about 10 - 12 feet.