I'm rather struggling with this so another question.

Caravan, alloy outer skin which is damaged and I need to repair it with
car body filler.

The problem is that car body filler is reputed to attack polystyrene
which is just behind the alloy skin and used for insulation. So I need
something to separate the two.

Your suggestions please.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On 5 Feb, 13:00, Harry Bloomfield
wrote:
I'm rather struggling with this so another question.

Caravan, alloy outer skin which is damaged and I need to repair it with
car body filler.

The problem is that car body filler is reputed to attack polystyrene
which is just behind the alloy skin and used for insulation. So I need
something to separate the two.

Your suggestions please.

--
Regards,
* * * * Harry (M1BYT) (L)http://www.ukradioamateur.co.uk


1) test attack theory first ?- whilst there test for attack on thick
polythene?

2) thick polythene tucked well in beyond the damaged area?

NB I mix up cbf on a supermarket plastic "worktop saver" - thin
flexible type usually translucent (& coloured)..

Jim K

On 05/02/2013 13:00, Harry Bloomfield wrote:
I'm rather struggling with this so another question.

Caravan, alloy outer skin which is damaged and I need to repair it with
car body filler.

The problem is that car body filler is reputed to attack polystyrene
which is just behind the alloy skin and used for insulation. So I need
something to separate the two.

Your suggestions please.


Hardboard/ aluminium foil? A blob of filler on the edge will hold it in
place while you do the rest

On 05/02/13 13:00, Harry Bloomfield wrote:
I'm rather struggling with this so another question.

Caravan, alloy outer skin which is damaged and I need to repair it with
car body filler.

The problem is that car body filler is reputed to attack polystyrene
which is just behind the alloy skin and used for insulation. So I need
something to separate the two.

Your suggestions please.

Almost anyth8ing.

epoxy does NOT attack polystryrene by the way so you could use epocy
filler instead.

Other possibles include simply slipping a bit of newspaper or plastic
bag in the gash and pushing it about a bit to protect the polystyrene.
Even painting it with PVA and sticking brown paper on will work.




--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Tue, 05 Feb 2013 13:00:23 GMT, Harry Bloomfield wrote:

Caravan, alloy outer skin which is damaged and I need to repair it with
car body filler.

The problem is that car body filler is reputed to attack polystyrene
which is just behind the alloy skin and used for insulation. So I need
something to separate the two.

I guess sliding something like ordinary cooking foil or a plastic bag
into the gap would be tricky. Ex takeaway container ali foil, Ex rigid
plastic food container, cardboard from cerial packet?

How big is the hole/damage? Will CBF stick well enough/be thick enough to
withstand the inevitable flexing of a caravan body?

--
Cheers
Dave.

Really, I know some car body filler gets hot as it cures, is this what you
mean.

Brian

--
From the Sofa of Brian Gaff Reply address is active
"Harry Bloomfield" wrote in message
. uk...
I'm rather struggling with this so another question.

Caravan, alloy outer skin which is damaged and I need to repair it with
car body filler.

The problem is that car body filler is reputed to attack polystyrene which
is just behind the alloy skin and used for insulation. So I need something
to separate the two.

Your suggestions please.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

It happens that Dave Liquorice formulated :
On Tue, 05 Feb 2013 13:00:23 GMT, Harry Bloomfield wrote:

Caravan, alloy outer skin which is damaged and I need to repair it with
car body filler.

The problem is that car body filler is reputed to attack polystyrene
which is just behind the alloy skin and used for insulation. So I need
something to separate the two.

I guess sliding something like ordinary cooking foil or a plastic bag
into the gap would be tricky. Ex takeaway container ali foil, Ex rigid
plastic food container, cardboard from cerial packet?

How big is the hole/damage? Will CBF stick well enough/be thick enough to
withstand the inevitable flexing of a caravan body?

Thanks, not so big an issue as I thought then. The actual exposed
polystyrene is about 2" x 2", though the damaged area is larger.

I was thinking along the lines of even the fumes from the filler
attacking the poly.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

Dave Liquorice formulated the question :
Will CBF stick well enough/be thick enough to
withstand the inevitable flexing of a caravan body?

I don't anticipate it flexing much at all, where it is located.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

Brian Gaff used his keyboard to write :
Really, I know some car body filler gets hot as it cures, is this what you
mean.

No, it is the chemical hardener in the filler which attacks the
polystyrene, it basically turns it into slime according to what I have
read. I just needed some advice on whether just keeping the two
separated was enough, or whether one needed to be sealed from the
other.

I saw a video of such a repair and they used some substance to seal
over the polystyrene, before applying the filler.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On 05/02/2013 16:18, Harry Bloomfield wrote:
Brian Gaff used his keyboard to write :
Really, I know some car body filler gets hot as it cures, is this what
you mean.

No, it is the chemical hardener in the filler which attacks the
polystyrene, it basically turns it into slime according to what I have
read. I just needed some advice on whether just keeping the two
separated was enough, or whether one needed to be sealed from the other.

I saw a video of such a repair and they used some substance to seal over
the polystyrene, before applying the filler.


Not quite true. Car body filler is mostly styrene monomer with an inert
filler, the hardner triggers polymerisation to polystyrene. The problem
is that the polystyrene foam insulation is somewhat soluble in the
liquid styrene but this should not cause real problems - particularly
once it is cured.

If you are worried about it getting hot, don't overdose it with the
hardner & it will cure more slowly. It will stick to polystyrene well
as it is all the same thing really but I guess might cause some of the
foam to collapse.

If a cavity forms in the insulation could it be injected with
polyurathane foam?

HTH

Chris K

On 5 Feb, 16:59, Chris K wrote:
On 05/02/2013 16:18, Harry Bloomfield wrote:

Brian Gaff used his keyboard to write :
Really, I know some car body filler gets hot as it cures, is this what
you mean.

No, it is the chemical hardener in the filler which attacks the
polystyrene, it basically turns it into slime according to what I have
read. I just needed some advice on whether just keeping the two
separated was enough, or whether one needed to be sealed from the other..

I saw a video of such a repair and they used some substance to seal over
the polystyrene, before applying the filler.

Not quite true. *Car body filler is mostly styrene monomer with an inert
filler, the hardner triggers polymerisation to polystyrene. *The problem
is that the polystyrene foam insulation is somewhat soluble in the
liquid styrene but this should not cause real problems - particularly
once it is cured.

If you are worried about it getting hot, don't overdose it with the
hardner & it will cure more slowly. *It will stick to polystyrene well
as it is all the same thing really but I guess might cause some of the
foam to collapse.

If a cavity forms in the insulation could it be injected with
polyurathane foam?

visions of caravans with bulging "hernias" on the M5 ;))

Jim K

On 05/02/13 16:10, Brian Gaff wrote:
Really, I know some car body filler gets hot as it cures, is this what you
mean.


No brian. one of the components of polyester resin is a sort of styrene
in a solvent. It does SLIGHTLY attack styrene.

But any physical barrier - even a layer of PVA - is enough for it to be
a non issue.

Brian



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On 05/02/13 16:10, Harry Bloomfield wrote:
It happens that Dave Liquorice formulated :
On Tue, 05 Feb 2013 13:00:23 GMT, Harry Bloomfield wrote:

Caravan, alloy outer skin which is damaged and I need to repair it
with car body filler.

The problem is that car body filler is reputed to attack polystyrene
which is just behind the alloy skin and used for insulation. So I
need something to separate the two.

I guess sliding something like ordinary cooking foil or a plastic bag
into the gap would be tricky. Ex takeaway container ali foil, Ex rigid
plastic food container, cardboard from cerial packet?

How big is the hole/damage? Will CBF stick well enough/be thick enough
to withstand the inevitable flexing of a caravan body?

Thanks, not so big an issue as I thought then. The actual exposed
polystyrene is about 2" x 2", though the damaged area is larger.

I was thinking along the lines of even the fumes from the filler
attacking the poly.

No. i've spray painted expanded polystyrene with cellulose paints. After
covering it with brown paper soaked in PVA. one pinhole caused a LOT of
damage..but the rest was fine.




--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

Chris K has brought this to us :
If a cavity forms in the insulation could it be injected with polyurathane
foam?

No, that would likely blow the walls out.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

The Natural Philosopher was thinking very hard :
But any physical barrier - even a layer of PVA - is enough for it to be a non
issue.

So it might be worth painting the exposed polystyrene with PVA as well
as adding a barrier?

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

Harry Bloomfield wrote:
Chris K has brought this to us :
If a cavity forms in the insulation could it be injected with polyurathane foam?

No, that would likely blow the walls out.

You were only supposed to blow the bloody doors off!

--
€¢DarWin|
_/ _/

On 6 Feb, 13:55, Steve Firth wrote:
Harry Bloomfield wrote:
Chris K has brought this to us :
If a cavity forms in the insulation could it be injected with polyurathane foam?

No, that would likely blow the walls out.

You were only supposed to blow the bloody doors off!

bet you can do the annoying nasal twang too?

Jim K