Cutting XPS insulation?

[Alan Ambrose]

I have a bunch (~72m) of Ravatherm XPS blocks 100mm x 600mm x 1,250mm I need to make some cuts reasonably accurately at 30 degree angles. Something like below, if you're looking from the ends of the boards.

 

Anyone have a great method? The cut surface on the slope is 200mm long.

[JohnMo]

Good luck - can I ask why?

[Conor]

Handsaw.

[-rick-]

Can you make one cut and flip the cut-off over to be the second piece?

 

Not got practical experience but I've seen people make a wooden jig with a hot-wire.

 

If you need to also cut the length of the board to make a single angled cut work, could do this with another hot-wire jig or track/table saw.

[BotusBuild]

26 minutes ago, Conor said:

Handsaw.

+1, and a facemask

[SimonD]

56 minutes ago, Alan Ambrose said:

I have a bunch (~72m) of Ravatherm XPS blocks 100mm x 600mm x 1,250mm I need to make some cuts reasonably accurately at 30 degree angles. Something like below, if you're looking from the ends of the boards.

 

Anyone have a great method? The cut surface on the slope is 200mm long.

 

What do you mean by reasonably accurate? I've used my jigsaw with a blade with 150mm cutting length on both woodfibre and eps at similar angles to this.  With this you need to make a jig so you have a flat surface on with the rest to jigsaw as it won't make the angle if using the large flat area of ther xps. The other option is to make up a plywood jig that sandwiches the xps and gives you a cutting guide to rest something like the Bahco insulation saw on. I'd probably for for the second option.

 

But if money is no object:

 

https://www.festool.co.uk/products/cordless-products/cordless-insulating-material-saw/577231---isc-240-eb-basic-gb

 

https://produkte.mafell.de/en/sawing/insulation-saw/insulation-saw-dss-300-cc

[Beau]

I would make up a 30 degree wooden wedge and use that to guide a handsaw at the angle.

[G and J]

Handsaw, straight edge, felt pen and practice. 
 

Draw a straight line both sides.  Stand the sheet up so the lines are vertical and cut watching the lines both sides.  
 

I think XPS is polystyrene so it’s easy to work, hand saw is ideal. I didn’t need a mask either (unlike PIR). 
 

One left field thought.  Polystyrene has a lambda of circa 0.034 thingys.  (Thingys stands for whatever the units are, I can’t be arsed googling it).  
 

Airtight foam has a lambda of 0.034 thingys too. 

[saveasteading]

Doing this currently.

Handsaw ( multipurpose) for small cuts. Circular saw for longer cuts. 

And mask, goggles, hat with the latter.

I had expected the eps to shed whole 'bubbles' but it cuts as very fine dust.

So do it indoors or you will contaminate the area.

[Mike]

If you have lots, then it could be worth getting a wavy-edge hand saw. I've got a Bahco ProfCut that works well and avoids the mess. Plus a knocked-up jig to keep the angle you want.

[Super_Paulie]

build a sled if you have loads to do? a sled and a hardpoint saw is what i used.

Edited Monday at 10:11 by Super_Paulie

[Alan Ambrose]

@JohnMo Pretty much this:

 

[Alan Ambrose]

Tried the tracksaw followed by handsaw idea today. Works fine, but we actually need the tracksaw at 60 degrees and it has a max of 45.

 

I've also ordered a hot wire cutter, a Bahco wavy saw and some Bosch wavy jigsaw blades to try.

 

Intend to build a jig somewhat like @Super_Paulie 's.

 

Will report back. 

[JohnMo]

Why not use mineral wool then zero cutting?

[G and J]

Or use several layers of thinner stuff cut square.   Will the small voids actually matter?

[Iceverge]

I'm wondering if this is a scenario where stepping the blocks and making up the diagonal difference with mineral wool is the massively simpler and no worse performing solution.

 

 

What's it for?

[G and J]

The way I read the diagram it’s to reduce the cold bridging at the sole plate.  
 

Otherwise cold air gets behind the plinth bricks.  
 

I assume there will be wall ties linking the walls and the plinth bricks.  Not sure how that will work with polystyrene sheets.  

[Alan Ambrose]

Good point about wall ties. I had thought about those, then forgotten about them…

 

Reporting back:

 

+ wavy Bahco saw hard to push through XPS even with wax on saw to help. Possible, but hard work and needs some skill to keep the cut flat - the saw tends to bow and then the cut ends up bowed.

+ wavy jigsaw blades also dodgy - causing lots of vibration presumably due to friction. Was actually melting the xps.

+ hot knife works ok but I need to think out some sort of jig to cut a uniform profile.

[saveasteading]

1 hour ago, Alan Ambrose said:

Reporting back:

I cant get the saw moving after a foot or so. Has to be a circular saw I think.  BUT we have professionals doing it on Monday   Monday EPS Tuesday PIR,  so I will be watching closely.

[-rick-]

1 hour ago, Alan Ambrose said:

+ hot knife works ok but I need to think out some sort of jig to cut a uniform profile.

 

I've seen someone do it by making the jig stationary and pushing the xps through it. Like a tablesaw/bandsaw. Vaguely remember that the standard wire was too flimsy to do at any speed but with a bit of juice and a thicker wire was able to get through it quite quickly. Thinking more, I have very vague recollections of someone using a welder as the power source (not sure it's the same one). In which case this is maybe not the easiest route to go down.