# Forum Home Renovation Landscaping, Gardening & Outdoors  Blue board screen fixing question

## harry hotspur

I am planning on constructing a blueboard screen in front of my fence which will be used to block out neighbours as well as to act as a projector screen in the summer. The screen will be 6 metres long by 2.1 metres high. I plan to use 3 metre rhs (75x75x1.6mm) and have them 900mm in the ground. I have 3 main questions: 
1) Will spacing the rhs joists at 750mm be sufficient to ensure no warping (total of 9 posts along 6 metres)?
2) what is the best method for attaching the cement sheets to the rhs box steel? I was debating hiring a coil gun but I have not used one of these before and have concerns whether the cement sheeting will split / crack / break under the pressure.
3) Does the blueboard / cement sheet require weatherproofing treatment as it is open to the elements?  
Any advise will be greatly appreciated (or alternative solutions) as I am still in planning stage....

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## harry hotspur

Update - I have decided to space the rhs box steel at 600mm and after discussions with the local hire shop, it appears that the coil gun is out of the question (having hired an auger to dig out the 11 holes). I dropped in to the Green Monster and they have suggested I use a bonding agent to adhere the boards to the steel, and then follow up with flush mounted screws spaced accordingly (having pre-drilled the holes in both the sheet and steel).

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## Bloss

Have to say that seems like engineering overkill to me. Why would you not use fewer uprights and use slightly larger railings? That is build the frame with railings complying with the need for 600mm spacing (effectively turning the usual wall frame on its side. Rails from treated pine (H3 would be OK - H4 if you wish). Fewer posts, fewer holes and easier to construct no predrilling into steel every 200mm! Fixings according to specs http://www.jameshardie.com.au/products/harditex.html. For that matter use H4-H5 TP posts too . . . unless you get steel really cheap.

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## harry hotspur

Bloss, you are probably correct in terms of over-engineering. However, the screen will sit at the end of a 6m x 6m patio (concrete slab). The slab finishes approx. 25cm from the fence and the space fills up with water from the run off. I have 6 metres of drainage channel (from Bunnings) which is approx. 11cm wide therefore giving me only a small space to work with. The steel comes in at about $300 (I have opted for 50x50mm except for the centre post which will use the 75x75mm for where I need to butt up the 3metre panels). The other reason for using steel is that I prefer to do a job once and then not have to worry about it again, plus the added benefit of everything being square to start with. What experiences have you had with cement sheets for exterior use - do you have any advise to avoid warping / twisting etc?

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## Bloss

They work fine for the sort of wall you propose. The main things is to fix to specs - and if there is any movement (from wind with a fence for example) then hairline cracks can appear in joins even if done to spec. But the current flexible joint compounds and textured finishes reduce that dramatically. I will be building a 2.4m high screening fence form it near my boundary in the next few months.

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## blute

Just got online to ask about the same thing. Im building a fence/screen around a pool. 
I've set 75x75x4mm SHS steel posts at 600 centers to take the joins of the sheets running vertically. The client wants cement sheet, however Hardies said there was no warranty if it was screwed directly to steel because of the expansion of the steel, no movement in the cement sheet etc. Has anyone fixed cement sheet directly to steel and had problems?? 
I have also considered recommending a ply cladding, like borals evolution cladding or shadow cladding? Anyone fixed this directly to 4mm steel?? 
Thanks

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