Cutting celotex type insulation

[Soylent1]

Just wanted to know if anybody had come up with an ingenious solution or some type of homemade jig for cutting celotex type insulation boards? anything up to 50mm is no problem it's just when you get the 70mm, 100mm its a real pain when you measure and mark out accurately and then you find you put a slight bevel on the cut because of the thickness of the board. My main issue is when installing between rafters, for example between 8'' rafters set back for 50mm air gap between felt and then leaving a 50mm gap at the front for 50mm board. I have tried putting a slight back bevel on deliberately and this is ok but not ideal as you have to remember to flip the board over or your next cut ends up with one side bevelled the wrong way! I have tried using a big circular saw and then finishing the cut with handsaw, this is really quite good however it makes a lot of mess and I can't stand the dust from the stuff! also you still have to spend a little time with a surf form to flatten the other side of your cut on the board. I might just be worrying about nothing but I can see there must be a better way.

And please nobody mention cutting too it too small and then using expanding foam to hold the board in (hammer) (hammer) (hammer)

 

[blackrodd]

You have it sussed! Use a decent handsaw, bevel the board, turn it over,etc, etc.
It normally pays to cut 4' way as 8' is far too long, You hear sometimes a bread knife or garden shears are use for the quilt insulation but they're no good for the "sheet" material.
Cutting with a decent handsaw and using some care, It is quite time consuming and should be done properly, cuts kept accurate and snug to get the best result from you're rather expensive insulation investment.
On some sites we would have to tape all ends and joints with a reflective alloy tape, and when directed by the architect or clerk of works, etc take down any area he or they requested to demonstrate the materials and workmanship were not compromised, The work should be done with care.
You ought to be wearing a mask, look at the light streaming in any window and see the really nasty stuff you're breathing in, And never use a power saw of any description.
Probably the commonest and therefore easiest mask to buy would be a 3M, ensure you have the PARTICLE filter,
Get one of those.
Get a mask or get an hours detention, or something worse in the future!
Regards Rodders

 

[RobinBHM]

Ive been fitting 120mm in between joists for my loft. Ive found cutting a bevel on one or both edges works well.

What is frustrating is that every joist spacing is different, the gaps arent parallel and the joists are mostly twisted. But apart from that and the itchy glass fibre dust and constant banging the head, its great fun

I use a standard hardpoint rip saw and keep it well waxed.

I did think about an indulation saw but heard they bind.

 

[Soylent1]

Thanks Rod, I always wear a mask, goggles, gloves and if I could I would wear an NBC suit and vacuum pack myself in polythene
I hate the damn stuff! it's obviously very good when it comes to being an insulator, but not so good for my temper/sanity. (hammer)
And thanks to Robin as waxing the saw sounds like a really good idea!

 

[Lons]

What Rodders said !

Goggles are a must so glad you list them as the stuff gets into your eyes as well as lungs.

the last big job I did was 130 sheets of 100mm and we were sick of the sight of it by the time we finished. Was 10 years ago and I still shudder at the thought of it. :lol:

 

[HOJ]

For cutting celotex I use a 4" paint type scraper with a ground edge on the sides and cut with a straight edge as a guide, no mess and a clean cut, and a big block of wood to knock it home.

You have to work your way through on thicker sheets but its the best way I have found.