Olly P

Preferred method for cutting PIR ?

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I have around 380sqm of 125mm PIR insulation to cut and install inbetween the rafters on our new build dormer bungalow.  I'm prepared that it will take me around 2 weeks to fit and I'm open to tried and tested cutting methods to get a straight, square and dust free cut. 

 

The go to is a worn handsaw but the dust is horrendous. 

 

Festool do a specific insulation power tool but its expensive and doesn't have the best reviews online. 

 

So I'm thinking of using my tablesaw using the fence and trying to get hold of a smooth blade for it to reduce the dust if they exist? 

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Table saw is a good shout... get some extraction on it too. Although in reality you will still be tweaking to fit with a hand saw anyway.

 

A bread knife works well too. 

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Really depends on quantity of cutting you have to do.

 

I use a scalloped breadknife outside for room scale projects, but you can get special saws for  little money. if you take that route spend about £8 on a garden steel sharpener and learn how to use it on a scalloped edge.

 

EG https://www.screwfix.com/p/bahco-wttpi-insulation-insulation-saw-22-560mm-/7498K?tc=KT68

 

Well worth it if you have any quantity to do.

 

Ferdinand

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Centrefire blades are designed for this:

 

https://www.amazon.co.uk/Bullet-Tools-Centerfire-Poly-ISO-Insulation/dp/B00RT0H66A

 

I'd still use dust extraction.

 

For the odd hand cut then the genuine Celotex, pink handsaws are great. If you can find one! Not sure they're still made tbh. They have serrated teeth.

 

I have bought & tried the Bahco insulation saw that has a "wavy" blade. Not great imo on above about 50mm, better for say Rockwool batts. Cutting pir square is key so less gaps to fill with squirty foam! Saying that some people deliberately cut it 5mm under and foam fill. 

 

 

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Without doubt the most unpleasant job, bar none, during our build.

 

We ended up cutting on a table saw, outside backs to the wind,  dust extraction full on , masks and face visors and still coughed and spat the whole time. 

Dreadful job. You have my sympathy. 

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At 125mm, even with a table saw you might have to flip your boards over. 

 

Maybe a "standard", very fine toothed large dia table saw blade  (like 300mm) would be better but with really good dust extraction.

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Table saws are good. I prefer to cut loose and foam in with a few nails halfway into the rafters

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In all seriousness, if I had a lot of thick PIR to do I'd experiment with grinding a hacksaw blade to fit into a jigsaw. Then grind the edges like a serrated knife edge.  I reckon you could set that up on a table and cut square.

 

https://m.ebay.co.uk/itm/Bosch-T313AW-Jigsaw-Blades-Serrated-Knife-Edge-Pkt-3-/353015428545?ul_ref=https://rover.ebay.com/rover/1/710-53481-19255-0/1?

Edited by Onoff

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I tried using a demo saw and it was quick but a bit dusty - best way was outside on a breezy day ..!!

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Table saw, but make yourself an 8x4 table

drop a sheet of ply over the table and then make some legs up for it. 

You can then screw a timber down as a long fence for cutting multiple cuts. 

Forget the extraction and set up a leaf blower pointing directly at the blade, any dust extraction gets blocked quickly, better to blow it away from you. 

Sod the neighbours. 

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I had 360 sheets of 75mm to do, found the quickest way was to use the insulation blade on the multitool to score through the foil, another run to cut through and then finish with the bahco saw to cut the foil backing. Horrible messy job, covered in PIR dust head to toe every day I did it. Tried using a face mask, zero help. I spent a couple of weeks eating/breathing PIR, horrible stuff.

Edited by LA3222

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Rather than a table saw, how about a band saw.  Would need to get one with a decent throat.

 

I use, for small jobs, a kitchen knife.  There is a very good chance I will stab myself one day.

 

And if you think the dust is bad, try cutting composite plastics, then you will know what bad is.

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1 hour ago, Onoff said:

In all seriousness, if I had a lot of thick PIR to do I'd experiment with grinding a hacksaw blade to fit into a jigsaw. Then grind the edges like a serrated knife edge.  I reckon you could set that up on a table and cut square.

 

https://m.ebay.co.uk/itm/Bosch-T313AW-Jigsaw-Blades-Serrated-Knife-Edge-Pkt-3-/353015428545?ul_ref=https://rover.ebay.com/rover/1/710-53481-19255-0/1?


what happened to the giant pizza cutter? Finish that before you start another project 🙄

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A bit slower, but making a hot wire cutter is pretty easy to do

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17 minutes ago, Vijay said:

A bit slower, but making a hot wire cutter is pretty easy to do

And breath in the arsenic fumes.  Best avoided.

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11 minutes ago, Vijay said:

A bit slower, but making a hot wire cutter is pretty easy to do

 

I tried...and failed. That is to say it worked using either nichrome or Kanthal wire. It sailed through foil faced PIR with ease. The big BUT was the wire kept breaking and eventually the random wall wart psu I was running it from gave up the ghost. I say random, I did do some VIR maths taking into account the length and resistance of the Kanthal. I imagine a thick enough wire with bfo, current controlled supply would work a treat.

 

 

 

 

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I use old wood saw the less flexible the better and  ground down the teeth with small grinder,so ends up cutting like large bread knife.

Easy to keep straight cut and very little dust but very clean cut!!

DSC02917.JPG

DSC02919.JPG

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Apologies for picture quality but hope you get the idea!

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1 hour ago, SteamyTea said:

And breath in the arsenic fumes.  Best avoided.

Lucky I've been doing it outside then lol

 

1 hour ago, Onoff said:

 

I tried...and failed. That is to say it worked using either nichrome or Kanthal wire. It sailed through foil faced PIR with ease. The big BUT was the wire kept breaking and eventually the random wall wart psu I was running it from gave up the ghost. I say random, I did do some VIR maths taking into account the length and resistance of the Kanthal. I imagine a thick enough wire with bfo, current controlled supply would work a treat.

 

 

 

I found getting the right tension on the wire and not pushing the material through too quickly really helped with that. I also designed mine to run straight off a 12v car battery ;)

Edited by Vijay

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Plenty of ways to cut this insulation, but I run a decent workshop Hoover next to me to catch most of the particles. Worked a treat

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I've used a table saw with extraction to cut 75mm celotex. Works just fine and does minimise the dust, but you need to made some proper infeed/outfeed tables if your doing it on your own.

Its quite satisfying when you have cut a perfect fit to go between your new and perfectly parallel floor joists.  

 

I do have a insulation saw from toolstation which is practically dust free. It has a wavy blade rather than teeth and feels like it could slice your finger up pretty well. Downside is that it can only cut a max of 75mm, even then it sticks pretty easily. O and its bugger to keep square without a decent guide.

 

+1 to the bandsaw idea. You would get a greater depth of cut and easier and safer than a circular saw. I believe you can get a small Record one for under £300 and it will do up to 120mm.

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