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Polystyrene - densities etc

General discussion on any topic which doesn't have a natural home on any of the other boards.
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mjcp
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Joined: 29 Jul 2015, 08:14
Location: A wind swept hill with no wind, in driving distance of Windsor, UK
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Polystyrene - densities etc

Post by mjcp »

Is it me or is there a wide variation in density, even among supposedly the same brand and "type" ?

e.g. Bought a 4 pack of Jabalite 50mm insulation board (50mm thick polystyrene sheets) that were uniform white particles

https://www.diy.com/departments/jablite ... 643_BQ.prd

Then needed some more (I'm teaching myself to hotwire wing cores!) and they had the same brand, and apparently the same type / package name etc, but the contents were a mixed white / black particle. These seem to me to be lower density. The resulting cores seem more flexible too and visually, they seem to have more gaps between particles too...

rant /over.

Marc
m̶j̶c̶p̶ Marc

Hanger -
Some (now) pristine models that are un-flown for a year.
Jolly Roger
Posts: 573
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: Polystyrene - densities etc

Post by Jolly Roger »

Sorry to hear that Marc. I have noticed that the black/white beaded foam is very weak and breaks off in big lumps. I think it may be recycled stuff. So you'll be saving the planet, although your wings may fold. :(
roo Hawkins
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Joined: 18 Mar 2015, 20:12
Location: Northamptonshire

Re: Polystyrene - densities etc

Post by roo Hawkins »

I have made wings out of the black and white stuff and have had no problems. I have add problems with blue foam wings bending after veneering and also blue foam delaminate when using latex glue.
Paul W
Posts: 11
Joined: 18 Nov 2015, 09:50

Re: Polystyrene - densities etc

Post by Paul W »

I've found the recycled white bead foam does vary in quality, I've bought batches where the black
bits are so hard it's impossible to get a good cut. Try and source virgin bead white foam if you can.

Better still is pink or lemon coloured XPS foam.

Like Roo, I've had problems with blue foam, though it's probably due to me not using it enough
to get my setup correct. I've heard that skimming the top and bottom 5 or 10mm off a block will
release the torsional forces inside so you don't get any twisting or bowing of the core.... not quite
sure how and why this works though!
Dave Mackintosh
Posts: 45
Joined: 26 Dec 2020, 19:02
Location: Cambridgeshire

Re: Polystyrene - densities etc

Post by Dave Mackintosh »

My current stock is from Wickes ,It has the black blobs in it ,but I'm happy with the density .It has a blue "hue" to it and is quite firm ,perfect for large scale spans.
I guess it's a case of grading as you purchase ,much the same as you would balsa.
I used to cut the shiny surfaces off of blue xps blanks as they formed a meniscus of sorts ,where once the core was cut ,the surface tension would curl the blanks.
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mjcp
Posts: 183
Joined: 29 Jul 2015, 08:14
Location: A wind swept hill with no wind, in driving distance of Windsor, UK
Contact:

Re: Polystyrene - densities etc

Post by mjcp »

Paul W wrote: 25 Apr 2021, 11:05 I've found the recycled white bead foam does vary in quality, I've bought batches where the black
bits are so hard it's impossible to get a good cut. Try and source virgin bead white foam if you can.

Better still is pink or lemon coloured XPS foam.

Like Roo, I've had problems with blue foam, though it's probably due to me not using it enough
to get my setup correct. I've heard that skimming the top and bottom 5 or 10mm off a block will
release the torsional forces inside so you don't get any twisting or bowing of the core.... not quite
sure how and why this works though!
Thanks!

So, where to find the pink / lemon XPS? It that a local thing or mail order typically?

M
m̶j̶c̶p̶ Marc

Hanger -
Some (now) pristine models that are un-flown for a year.
Mick Tomlin
Posts: 35
Joined: 18 Mar 2015, 10:22
Location: East Sussex

Re: Polystyrene - densities etc

Post by Mick Tomlin »

Try Sheffield Insulation or SIG.
They have branches all over the country.
Worth also trying local roofing contractors.
They often have offcuts that suit our requirements.
Hope that helps.
Mick
Paul W
Posts: 11
Joined: 18 Nov 2015, 09:50

Re: Polystyrene - densities etc

Post by Paul W »

mjcp wrote: 26 Apr 2021, 12:27

So, where to find the pink / lemon XPS? It that a local thing or mail order typically?

M
As Mick says, try and track down a local insulation supplier. I've found one in the
past that gave me several sheets (which they'd cut incorrectly or were damaged)
in exchange for a contribution to their tea and biscuit fund.
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