Rendering on to timber

[Tux]

Hi crazy plasterers! Been reading your excellent tips and advice for a couple of weeks and thought i should get involved, so thanks and i hope i can repay the favour in the future.

I have been rendering a large extension with s&c however it has a bay window that is ply on the outside. The less than compatent builders have left it a bit like a hexagon and i now need to create a perfect curve, can anyone please help as to what i should put on the timber before rendering. I have used expanding metal for small areas in the past but dont think this alone will work for such an area where the render will be fairly thick in places.
Any advice is greatly appreciated : :

 

[bigsegs]

if it was me mate i'd do what you suggest, use eml sheets, well fixed, but with polythene over the timber first..
then id stick a thin coat over the metal, let that go off then start to build it up.
when i'd got it just about covered id get hold of some plastic pipe, maybe 20mm overflow pipe and bend it round the bay, one at the top bout 4" down, one at the bottom 4" up and fix em at the ends, one in the middle...tricky but it'll give you the curve you need, just got to get em equal then youll be laffin..
then i'd build it up a layer at a time scratching every coat and ruling the final scratch coat off the pipe... then remove the pipe, fill in the strip and apply the float coat...
thinking on it might pay you to batten off the eml with some roofing lath vertical first and leave an air gap at the bottom where the drip bead would go, depends on your window set up below...it'll stop it sweating..

 

[Tux]

if it was me mate i'd do what you suggest, use eml sheets, well fixed, but with polythene over the timber first..
then id stick a thin coat over the metal, let that go off then start to build it up.
when i'd got it just about covered id get hold of some plastic pipe, maybe 20mm overflow pipe and bend it round the bay, one at the top bout 4" down, one at the bottom 4" up and fix em at the ends, one in the middle...tricky but it'll give you the curve you need, just got to get em equal then youll be laffin..
then i'd build it up a layer at a time scratching every coat and ruling the final scratch coat off the pipe... then remove the pipe, fill in the strip and apply the float coat...
thinking on it might pay you to batten off the eml with some roofing lath vertical first and leave an air gap at the bottom where the drip bead would go, depends on your window set up below...it'll stop it sweating..

Cheers bigsegs, lovelly idea using the pipes to form the curve!
When you say polythene do you suggest a tarpauline/visqueen type thing.

 

[bigsegs]

yeh visqueen dpm or similar, it'll work as a vapour barrier