# Accurate cutting of PIR insulation.



## Zedheadsteve (18 May 2019)

Sorry, more a of a construction topic than woodwork. Any recommendations for fitting PIR insulation? I have successfully used a small Dewalt site table saw to fit a little 100mm PIR very square and snuggly to joist and stud work. I cannot personally do this as well with a hand saw or knife type blade. Trouble is of course, the site saw or a circular saw generates lots of nasty dust. Need to do this outside and with really good mask and goggles, but still not happy in terms of environment or health.

Anyone tried the Festool 240 with extraction?

Steve


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## SammyQ (18 May 2019)

Steve, '40tonne wrecking ball to shell a peanut' occurs to me? Are you seriously SO far out when you use a disposable 'hardpoint' that a slightly oversize square of PIR doesn't squash fit? A similar shaped, but slightly smaller, ply offcut and a rubber mallet are also handy for persuasion into the desired compartment. On the odd occasion that I boo-boo and cut short, a 1-second squirt of expanding foam, time, and said hardpoint to trim flush, have proved more than adequate. 

Hoping I have not missed something obvious, Sam.


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## johnnyb (18 May 2019)

we have a great system. we use a track saw with a 3m rail. coarse blade with slowest speed and extraction. it wont go right through 100 but it makes easy accirate cuts. cut from both sides and finish with a saw. our cuts are nearly perfect fit.


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## johnnyb (18 May 2019)

also knock in with a lead dressing tool.


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## johnnyb (18 May 2019)

anyone whose fitted lots of this knows its not a job for a hardpoint saw and dodgy cuts. remember most roofs need 6 or 7 inch of this! 
personally only the apprentice does it by hand.


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## MikeG. (18 May 2019)

..........or cut it undersize, wedge it into place, and use expanding foam to fill all round.

The idea that the Celotex has to be cut dead square is amusing, considering how twisted the timbers will be that it's fitted to. And of course all those joists or rafters will be dead straight and parallel, won't they.


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## Deadeye (18 May 2019)

Zedheadsteve":2wfnp905 said:


> Sorry, more a of a construction topic than woodwork. Any recommendations for fitting PIR insulation? I have successfully used a small Dewalt site table saw to fit a little 100mm PIR very square and snuggly to joist and stud work. I cannot personally do this as well with a hand saw or knife type blade. Trouble is of course, the site saw or a circular saw generates lots of nasty dust. Need to do this outside and with really good mask and goggles, but still not happy in terms of environment or health.
> 
> Anyone tried the Festool 240 with extraction?
> 
> Steve



Just before I got put out of commission by surgery I insulated my workshoip (garage) ceiling. The joists were neither evenly spaced nor parallel, and there were random bits of electric/bracing and pillar to work round. The above sums up the approach exactly. I'm not great with foam, but I don't think I have lost many conductance points.


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## SammyQ (18 May 2019)

Johnnyb? Not all of us are 'in the trade' with all the toys or have deep enough pockets to afford the Male Festeringtool Jewellry...  
Speaking as a time-served and indented amateur, the two houses I renovated/insulated were well served by a hardpoint and careful laying out. 
Gotta say though, that feckin polymacstyrene 'bobble' dust gets everywhere :shock: and sticks to everything  ! Good extraction, humble vacuum, both are a God-send!
Sam, now a convert to Kingspan.


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## Lons (18 May 2019)

About 12 years ago when I fitted well over 100 8x4 sheets during a stable conversion. tried the handsaw but dust was horrible so bought some cheap semi flexible, thin bread knives and we cut the lot with those using straightedges. It was so effective I used them ever since. 
Only modification was to wrap the knife handles with foam for comfort.


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## Trevanion (19 May 2019)

Lons":fmbqoz5g said:


> thin bread knives and we cut the lot with those using straightedges. It was so effective I used them ever since.



I think you can buy proper insulation handsaws that are basically a longer bread knife :lol: No teeth just a wavy (serrated? not too sure) edge. I imagine there's barely any dust with one of those.

It really depends on how much you've got to put in, if you've only got 100 sheets to do or so you'd be an silly person to think about buying anything more than a handsaw to cut it up. If you're planning on putting in tens of thousands of sheets over years and years and that's your only job perhaps it's worth investing the money in some shiny green nonsense but everyone I've ever seen on site will always cut it in with a hand saw because it's quick and cheap. By the time you set up a cut with one of those Festool jobbies, I wouldn't be surprised if some people I know would've already done a wall by the time you've finished the cut.


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## Doug71 (19 May 2019)

johnnyb":ef4z923f said:


> we have a great system. we use a track saw with a 3m rail. coarse blade with slowest speed and extraction. it wont go right through 100 but it makes easy accirate cuts. cut from both sides and finish with a saw. our cuts are nearly perfect fit.





SammyQ":ef4z923f said:


> Johnnyb? Not all of us are 'in the trade' with all the toys or have deep enough pockets to afford the Male Festeringtool Jewellry...
> Speaking as a time-served and indented amateur, the two houses I renovated/insulated were well served by a hardpoint and careful laying out.
> Gotta say though, that feckin polymacstyrene 'bobble' dust gets everywhere :shock: and sticks to everything  ! Good extraction, humble vacuum, both are a God-send!
> Sam, now a convert to Kingspan.



The Festool tracksaw is the cheap option, this is the proper tool for the job

https://www.kelvinpowertools.com/festoo ... gItGPD_BwE


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## Lons (19 May 2019)

Trevanion":saj97uhu said:


> It really depends on how much you've got to put in, if you've only got 100 sheets to do or so you'd be an silly person to think about buying anything more than a handsaw to cut it up. If you're planning on putting in tens of thousands of sheets over years and years and that's your only job perhaps it's worth investing the money in some shiny green nonsense but everyone I've ever seen on site will always cut it in with a hand saw because it's quick and cheap.



The 100 odd sheets felt like 1000s at the time, I assure you. :lol: :lol:


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## johnnyb (19 May 2019)

wow i never expected any annoyance from my response! anyway i use makita! if youve got 20 100mm sheets and own a track saw and a vac buy the 3m rail its well worth it.100mm sheets wont cut with a bread knife or a celotex saw. its to deep. 
any joiner thats going to be doing the insulation will make sure his joists are evenly spaced. as a job cutting insulation is dreadful cutting a house size amount is really dreadful. 
we write the size on the adjacent joist top and bottom. cut exact size. 80% it goes in 20% in needs adjusting. its satisfying as well getting a really good fit. ok some caveats a fast wood circular saw can and will bind. a table saw is worse . most dust gets in your eyes when your knocking in. accurate cutting helps hugely.
btw this tip is a product of experience...take it or leave it but those insulation saws by festool are really meant for bats not pir.yes they make a special blade but the concept is for bats.slow blade speed on the track saw is the key.


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## johnnyb (19 May 2019)

also 100 sheets of 100mm kingspan would be what £4000-5000. a few weeks worth of work fitting. not really a small amount tbh. it would be a pile 10m high.


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## Zedheadsteve (19 May 2019)

Yes the material costs are v. high compared to the tools. If they makes the job better and especially quicker then they tend to pay for themselves. Producing scrap or not doing stuff right first time is just pure waste.


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## SammyQ (19 May 2019)

> "wow i never expected any annoyance from my response!"


  No annoyance generated or umbrage taken Johnny, just gently pointing out some of us forumites are not in the trade and don't have the tools to diversify sideways into cutting Celotex/Kingspan. Or, the 'greenbacks' (that shows my age) to swank a Cesspool, sorry, Festool, wotsit. Nae probs Big Lad.  

Bob? Did you REALLY cut all those sheets by hand? You must have looked like a teddy bear at each day's end...respect. 

Sam


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## MikeG. (19 May 2019)

johnnyb":2bdc97w6 said:


> wow i never expected any annoyance from my response!.......



You didn't get any. Don't confuse people having a different opinion from you with people being annoyed with you. There's usually a dozen different ways to skin any particular cat, and someone choosing a different way from you doesn't imply that yours is wrong, or that there is any emotional attachment to the discussion about cat skinning.


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## SammyQ (19 May 2019)

Wot Mike said. Better than I did.

Sam


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## johnnyb (19 May 2019)

i can see that now guys.


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## Jacob (19 May 2019)

MikeG.":36lbsojg said:


> ..........or cut it undersize, wedge it into place, and use expanding foam to fill all round.
> 
> The idea that the Celotex has to be cut dead square is amusing, considering how twisted the timbers will be that it's fitted to. And of course all those joists or rafters will be dead straight and parallel, won't they.


Yep. Even if you cut it with a precise TS it still won't fit and you have all the dust to contend with.
Done loads in the past with a lath for straightedge, a felt tip, a tape, and a panel saw - doesn't even have to be very sharp! A long surform plane thing is good for taking of bumps from the edges


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## Lons (19 May 2019)

SammyQ":1m77a1ms said:


> Bob? Did you REALLY cut all those sheets by hand? You must have looked like a teddy bear at each day's end...respect. Sam



There were 3 of us cutting / fitting Sam and we rotated to ease the task. It was only 60mm thick and 3m x 2m not 8 x 4 as I said but from memory the quantity was probably over 150 sheets, I'd have to look at the old invoices to be sure, and the work was spread over weeks because it was a large conversion so no real problem. I kept the bread knives really sharp and use a slicing rather than sawing cut so very little dust except when knocking it into place and if it was a bit tight easy to just trim a fraction off using the frame timber as guide

The worst problem with that job was having to use a lime mortar mix and do the mixing on a windy exposed site, there was a huge amount of stonework plus pointing to all the original and all the garden and boundary walls.

When we started, it was a stable still housing a couple of horses but just a crumbling shell with no innards or upper floor, grade 2 listed but the planners wanted to allow it to fall down rather than be converted so it was a fight all the way. Worked though and my mate sold it at Christmas for £730k, he's a bit pi**ed at me 'cos I refused to work on his new gaff, too busy playing golf. :lol: 

How are your 2 little friends doing at the minute btw?


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## SammyQ (19 May 2019)

They are as much a nuisance as you would imagine, so I have decided - after excellent professional advice - to sever all links with them! Contractual deadline Thursday next. :-" 

Sam


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## Lons (19 May 2019)

Hope separation isn't too painful, you could always turn to the demon drink to numb the senses for a while. :wink:


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## SammyQ (19 May 2019)

Ah!! "De watter of Loife", Uisce beatha, as some call it...got some "third run" tucked away somewhere... \/ 

Sam


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## Phil Pascoe (19 May 2019)

A bottle of Black Bush goes down wonderfully.


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## SammyQ (19 May 2019)

The visit to the distillery is something else...they encourage you to sniff the mash tuns... :shock: all that CO2 is like an electric shock! 
Sober Sam


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## TFrench (19 May 2019)

I'm a lagger and all I have is a trusty aldi kitchen knife :lol: To be fair we do very little thick kingspan work, when we do though its a worn out hardpoint saw. The insulation knives with the serrated blade are ok, not amazing in kingspan. Excellent in mineral fibre though, as are the saws with the wavy blade. It's my line of work and I can't imagine why anyone would buy the festool insulation saw. I've not seen one on a site yet...


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## Bm101 (20 May 2019)

Just a thought.. probably a daft one. When I was a nipper, my cousins (same age) who didn't really do the whole jumpers for goalposts type childhood were however a dab hand at making stuff. Like these paper hawks you had to cut out and delicately fold. It would take them _days._ 
They looked good, brilliant really, hung up on the ceiling.





but then they'd start explaining the whole intricate process and 8 year old me suddenly was all 





Bear with me here.
One of the things they did was cut out polystyrene. F*** knows why. I can't remember I was too busy falling out of trees and believing you could straighten Bmx mags by just putting them in the freezer. :| But for some reason I have never forgotten they modeled it using a hot wire filament and it would cut it super clean and super quick. 
Gotta be worth a go hasn't it if you have a lot to do?
Car battery. Ply base with a hole drilled for the element (small OD steel round bar etc) and some method of fixing it in place. Wee think and you'd make the rod as a part you could add and remove to any sheet going just by drilling a small hole in the mdf etc. Weld it to a bit of plate with space to add a jump lead underneath the bed etc and screw it on.... You could add a slot at either end for a straight edge as a guide with clamps if you could make it fast enough to be practical. More likely score the foil and just do it by eye. Whack the top jump lead on and you're off. 
Bosh!
Hse will love this stuff.


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## TFrench (21 May 2019)

If you really want to know the secret to it? Score it with a sharp knife, flip it it over and karate chop it. Works a treat up to about 75mm thick. You can do it with 100mm but you have to be a bit more... brutal with it :lol:


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