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100mm Celotex rigid insulation board installation advice and tips?

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baldkev

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yes to hand saw or big knife. Cut slightly oversize so it's a tight fit.
Power saw really bad with dust everywhere, and no faster.
I gotta pull you on that one, a circular saw with a guide ( i welded myself a t shape about 700mm long that fits in my saw guide holes ) is way quicker and more accurate. Its square all the way, no wander.
A table saw is even quicker again. I have a dw745 with site extractor ( yes, still some dust gets thrown about ) but its so fast and repeatable. If you are cutting over 70mm, you flip the sheet and run again, perfect cut.... i usually aim for 1mm under and its always a tight fit
 

Jacob

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I gotta pull you on that one, a circular saw with a guide ( i welded myself a t shape about 700mm long that fits in my saw guide holes ) is way quicker and more accurate. Its square all the way, no wander.
A table saw is even quicker again. I have a dw745 with site extractor ( yes, still some dust gets thrown about ) but its so fast and repeatable. If you are cutting over 70mm, you flip the sheet and run again, perfect cut.... i usually aim for 1mm under and its always a tight fit
Tried both but settle for the 26" handsaw mainly because of the dust, but in fact more convenient and no slower (like hot knife through butter etc) and plenty accurate enough to a felt tip line from straightedge.
 

Stuart Moffat

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By the time you have drawn your felt tip line Jacob, the rest of us will have already made a guaranteed straight cut, and it won’t have small air leaks that need taping or foaming.
 

Jacob

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By the time you have drawn your felt tip line Jacob, the rest of us will have already made a guaranteed straight cut, and it won’t have small air leaks that need taping or foaming.
Only if the spaces between joists/rafters are perfectly straight to start with, and you are close to your TS with a 4" depth of cut.
With a 26" hand saw its only two or three strokes through 48" of 4" celotex board. If you are working your way through attic rooms moving the TS would take up half the time as well as needing a dust extractor.
My TS would need four blokes to shift it and have to be dismantled to get it through doors. Then there'd be the dust extractor..... :unsure:
 

Stuart Moffat

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Then you have a very weird track saw! and you have rather ignored the OP‘s opening comment that he wasn’t impressed with a handsaw and was looking for something better.
 

baldkev

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Only if the spaces between joists/rafters are perfectly straight to start with, and you are close to your TS with a 4" depth of cut.
With a 26" hand saw its only two or three strokes through 48" of 4" celotex board. If you are working your way through attic rooms moving the TS would take up half the time as well as needing a dust extractor.
My TS would need four blokes to shift it and have to be dismantled to get it through doors. Then there'd be the dust extractor..... :unsure:
2 or 3 strokes? What do you cut with? A lightsabre? Id love to see a video of that....
But no need to move the ts once set up, i generally take the materials to the saw 😉
 

Jacob

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2 or 3 strokes? What do you cut with? A lightsabre? Id love to see a video of that....
But no need to move the ts once set up, i generally take the materials to the saw 😉
Have tried cutting Celotex with a hand saw? It's really easy. Big 26" hand saw, not a back saw or a fret saw.
Chapel conversion. 3 floors. Taking material to the saw would have involved hundreds of journeys to and from the saw, not to mention the noise, dust, size of sheets. Taking saw to material really easy.
 

baldkev

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Have tried cutting Celotex with a hand saw? It's really easy. Big 26" hand saw
I have, many times, but never once did i manage to rip a sheet of celotex in 3 strokes.... it does ( for me ) take quite a few strokes and a bit of care, to cut a slice of celotex straight and square..... but now ive moved on and use my site tablesaw. I applaud your use of handtools etc, but there are other ways too and some are quicker, some are more accurate and some are quicker and more accurate...... for a site carpenter now, you have to move quickly but still with good accuracy to earn money.

Gone are the days of taking years to build houses with handtools and lots of blokes. Even during my 24/25 years, things have advanced dramatically. Even down to regularised 4x2s etc speeding stuff up. Lots of change, embrace it 😚🫂
 
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Tazio

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Try the festool insulation saw brilliant bit of kit does require building a cutting bench though to get the best out of it !
 

Jacob

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I have, many times, but never once did i manage to rip a sheet of celotex in 3 strokes.... it does ( for me ) take quite a few strokes and a bit of care, to cut a slice of celotex straight and square..... but now ive moved on and use my site tablesaw. I applaud your use of handtools etc, but there are other ways too and some are quicker, some are more accurate and some are quicker and more accurate...... for a site carpenter now, you have to move quickly but still with good accuracy to earn money.

Gone are the days of taking years to build houses with handtools and lots of blokes. Even during my 24/25 years, things have advanced dramatically. Even down to regularised 4x2s etc speeding stuff up. Lots of change, embrace it 😚🫂
Taking 8x4 sheets to a table saw would take a big saw and ideally two blokes. Carrying the pieces around the building would need a little team especially if there were stairs and passages. Much easier to take the saw to the material, over a couple of saw horses. Much easier to saw with a long hand saw (for the reach and depth) than manoeuvering a much heavier track saw and the necessary dust extraction kit, for each cut. Can you get 4" tracksaws?
 

owen

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Taking 8x4 sheets to a table saw would take a big saw and ideally two blokes. Carrying the pieces around the building would need a little team especially if there were stairs and passages. Much easier to take the saw to the material, over a couple of saw horses. Much easier to saw with a long hand saw (for the reach and depth) than manoeuvering a much heavier track saw and the necessary dust extraction kit, for each cut. Can you get 4" tracksaws?
A tracksaw helps, if you cut the first 50mm with a tracksaw then cut right through with a handsaw you do get a straighter cut. The labourers normally get this job with us, so trying to get them to cut in a straight line is hard work. We find the extra time spent using the tracksaw is worth it, compared to the time spent trying to straighten cuts afterwards.it also saves a lot of dust flying around.
 

Jacob

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A tracksaw helps, if you cut the first 50mm with a tracksaw then cut right through with a handsaw you do get a straighter cut. The labourers normally get this job with us, so trying to get them to cut in a straight line is hard work. We find the extra time spent using the tracksaw is worth it, compared to the time spent trying to straighten cuts afterwards.it also saves a lot of dust flying around.
Seems a lot of bother, cutting twice a heavy electric saw and a hand saw. More practice with the hand saw for a straighter cut? Certainly be a lot faster.
I seem to recall cutting to the line or slightly over but undercutting a very slight bevel, so the piece would then be a tight fit wedged between rafters
 

owen

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As for moving it around, you cut on the stack of boards so you're actually moving materials less.
Seems a lot of bother, cutting twice a heavy electric saw and a hand saw. More practice with the hand saw for a straighter cut? Certainly be a lot faster.
I seem to recall cutting to the line or slightly over but undercutting a very slight bevel, so the piece would then be a tight fit wedged between rafters
Tracksaws are not heavy, don't know where youve got that from. Cutting a bevel makes it even more work because then you have to flip the board around for the next cut and cutting a straight bevel cut in this stuff isn't very easy. Honestly, if we had a room of 50mm kingspan to do in-between studwork, I could cut all of it with a tracksaw in the time it would take you to do half with a handsaw. I do the long cuts with the tracksaw, normally 355 on 400mm center studs, cut a load of pieces that size one after another then take the pieces to the wall and cut them to length with a handsaw. I've done it both ways, lots of times, and tracksaw always wins for me.
 

owen

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Another thing you're forgetting is marking out, by the time you mark either end, drop a straight edge on and mark a line to cut, you may aswell just mark either end drop the track on and make the cut
 

Jacob

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Just found a bit of 3" kingspan in the workshop. Couldn't resist temptation so did a trial cut with a 26" hand saw. It cuts 4" on the backstroke and 12" on the fore stroke. So that'd be 3 full strokes through a 48" board. In about 4 seconds. Pretty much what I remembered.
No noise, very little airborne dust but a lot of crumbs.
Can be as straight as you want - some may need a little practice!
I've got a 28" rip saw which I guess would be even faster.
 

owen

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Just found a bit of 3" kingspan in the workshop. Couldn't resist temptation so did a trial cut with a 26" hand saw. It cuts 4" on the backstroke and 12" on the fore stroke. So that'd be 3 full strokes through a 48" board. In about 4 seconds. Pretty much what I remembered.
No noise, very little airborne dust but a lot of crumbs.
Can be as straight as you want - some may need a little practice!
I've got a 28" rip saw which I guess would be even faster.
I've just cut a piece of 50mm kingspan, cuts in approx 1/2 a second with a tracksaw and no dust at all. You're stuck in the stone age.
 

Jacob

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I've just cut a piece of 50mm kingspan, cuts in approx 1/2 a second with a tracksaw and no dust at all. You're stuck in the stone age.
You are stuck in the expensive unnecessary gadget age!
Have you got a few "systainers" too? They used to be called "boxes" when ar worra lad. 🤣
 

owen

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You are stuck in the expensive unnecessary gadget age!
Have you got a few "systainers" too? They used to be called "boxes" when ar worra lad. 🤣
😅😅 Sure, if I didn't have my tracksaw, the amount of work I'd get done everyday would more than half. I do have one systainer, it's the one the saw got delivered in and hasn't been put back in since 😅.
 

Lefley

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I am half way through doing triple a garage roof using 140mm. The best ways that I found are using a tracksaw, then turn it over and score it with a knife if it hasn’t gone all the way through. Alternatively a jigsaw with a long blade works well. Dust control is essential. I found a handsaw with that thickness was impossible, but yours is thinner so you might be ok.

If your rafters are like ours you will never get a perfect fit. It’s better to be under and use foam than try to force it in. If you have got it really wrong (and by really it only needs to be a couple of mm under not to stay put), use little nails in the rafters to support it then use foam.

Invest in a foam gun where you have a better chance of getting the foam where you want it Instead of on your head. Also be prepared to layer the foam for larger holes as you are never quite sure how much it will expand.

if it’s any consolation you will be good at it by the time you get to the end!
We do a lot of net zero houses in Canada. 300-400 mm foam insulation screwed to the roof after cross strapped with 1x4 ( inch) then metal roofing. We only use a handsaw to cut. And it’s bloody hard putting a 375 to 475 mm screw through insulation and hitting a 1 1/2 ( inch) wide truss,
 

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Robin Clevitt is an advocate of ‘gappotape’.
Clevett doesn’t have to pay for it thats why he uses it…..
just use a long Bosch jigsaw blade.
any gaps foam them trim it off once dried and silver tape it.
 
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