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Author Topic: Foam for body shaping  (Read 817 times)

RhysN

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Foam for body shaping
« on: 28 July 2020, 08:32:55 am »
As I am somewhat averse to using my costly epoxy for making body shapes, and even more so to wrapping large bubble polystyrene with foil to prevent polyester resin attack, I have been trying to find cost effective foam which polyester resin does not attack.
And I have found it. It's Celotex which is available from place like Wickes. I have acquired some damaged part sheets for not much (they are glad to get rid of it). The foil is a bit of a pain to peel, but it shapes beautifully to a very fine finish.
Cut with hand saw, and then shape with blocks of what you cut off as sanding blocks.
Marek, I need your filming skills to do a "how to".

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Graham Hill

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Re: Foam for body shaping
« Reply #1 on: 28 July 2020, 11:47:43 am »
Yes I used this for part of my boat tail and its great to work with.
Don't get it too hot though, I've just added heat-reflective protection from my flow-through exhaust; I had smoke and ash to contend with at our last Stretton meeting from a combination of smouldering plywood and Celotex.
This is the insulation type used at Grenfell Tower: generally safe, but under certain circumstances it will ignite.

RhysN

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Re: Foam for body shaping
« Reply #2 on: 28 July 2020, 01:16:25 pm »
I have never left the foam behind after glassing! Once it's glassed there is no reason to leave it in place.
According to the Celetex site, their foam was not generic to that used at Grenfell, and is cleared for all buildings.  Of course polystyrene is truly horrible with flame!
« Last Edit: 28 July 2020, 01:27:30 pm by RhysN »

Chris Brown

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Re: Foam for body shaping
« Reply #3 on: 28 July 2020, 02:14:41 pm »
Celotex is polyurethane foam, exactly what I acquired some months ago from a local builders months ago. That's the stuff I was talking about using Gorilla Glue to bond if you recall Rhys, as that's a polyurethane glue, and should have similar sanding characteristics to the foam.

RhysN

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Re: Foam for body shaping
« Reply #4 on: 28 July 2020, 07:00:40 pm »
I have carved a lot with polyurethane, one of the things I learned decades ago was to keep the glue line away from where you want to carve as it forms a harder line that doesn't shape the same.
Celotex claim to be  polyisocyanurate foam. I have no idea if that's different from polyurethane, but it certainly shapes differently.
From google
The greater bond strength also means these are more difficult to break, and as a result a polyisocyanurate foam is chemically and thermally more stable; breakdown of isocyanurate bonds is reported to start above 200 °C, compared with urethane at 100 to 110 °C. ... By comparison polyurethane indices are normally around 100.
« Last Edit: 28 July 2020, 07:03:00 pm by RhysN »

Adrian

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Re: Foam for body shaping
« Reply #5 on: 28 July 2020, 10:17:04 pm »
If you get some blue foam, shape it, cover it in glass cloth and resin and then, when its cured (next day) you can dissolve the foam away completey with thinners leaving you with a nice thin GRP shell and a very messy floor.
You still have to fill and sand of course but it works well. Takes a lot of thinners though.

RhysN

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Re: Foam for body shaping
« Reply #6 on: 29 July 2020, 08:18:42 am »
If you get some blue foam, shape it, cover it in glass cloth and resin and then, when its cured (next day) you can dissolve the foam away completey with thinners leaving you with a nice thin GRP shell and a very messy floor.
You still have to fill and sand of course but it works well. Takes a lot of thinners though.

Blue foam is polystyrene, hence my initial comment about epoxy. Petrol dissolves the blue foam too.

Marek.Z.N

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Re: Foam for body shaping
« Reply #7 on: 29 July 2020, 10:26:51 am »
I wouldn't recommend using petrol to dissolve polystyrene as that is how you make napalm  ;) interesting body making technique though. I am still deciding what to make my bodywork out of so its interesting to see/hear a few more options

RhysN

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Re: Foam for body shaping
« Reply #8 on: 29 July 2020, 11:32:08 am »
I wouldn't recommend using petrol to dissolve polystyrene as that is how you make napalm  ;) interesting body making technique though. I am still deciding what to make my bodywork out of so its interesting to see/hear a few more options
I don't imagine thinners is a whole lot better !

TheGiantTribble

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Re: Foam for body shaping
« Reply #9 on: 29 July 2020, 01:47:24 pm »
I do know some people, when they use large cell polystyrene, wrap it in brown packaging tape to protect it from the resin. Please note I havnt tried this myself.

RhysN

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Re: Foam for body shaping
« Reply #10 on: 29 July 2020, 05:34:25 pm »
I do know some people, when they use large cell polystyrene, wrap it in brown packaging tape to protect it from the resin. Please note I havnt tried this myself.
My issue with the large bubble is mainly that it's very easy to tear lumps out of your shape and that even the fumes from  polyester can soften your plug.
So, a little more to spend on the foam, better shaping facility and a better outcome. Polyester resin is, of course, cheaper than the option of epoxy, and I find polyester more friendly to work with. Yes I know there are some health issues, but then epoxy isn't free from those either.

Adrian

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Re: Foam for body shaping
« Reply #11 on: 01 August 2020, 08:38:00 pm »
Personally I dont like using foam at all.
I know its easy to sand but its difficult to shape.
In fact I find it difficult to make a symetrical shape with it at all, it's always too 'freehand' for me. If I was making a boat hull (and I have made lots) I would make the bulkheads and plank it and thats what i would do with a car body. Once the planking is on gaps get filled with Easy Sand and the result is perfect.
In my experience using foam to fill in between bulkheads doesn't work very well either because you can always 'see' the bulkheads in the finsihed job no matter how hard you try.
The blue foam route may be shorter but you will have to live a long time with the consequences.