Foam inside wheel arches

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Dave Summers
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Joined: 9th May 2007 - 8:10pm
Location: Culloden, Inverness

Foam inside wheel arches

Post by Dave Summers » 31st August 2020 - 9:16pm

I've been cutting rust out of the rear wheel arch on my 412, and the cavity is filled with some yellow foam stuff which I presume is meant to inhibit rust as well as absorb sound or vibration. I've dug it away from the immediate area (just a few mm so far) but I'm wondering how flammable it is - I don't want to find out the hard way when welding! Also if I remove a lot of it, what would folks recommend as a good rustproofer to inject into the space once the repair is done? Waxoyl is obvious but if I'm right in thinking the foam is also meant to absorb vibration, there may be something more suitable.
So far I'm on the forward part of the wheel arch, but there's another hole in the inner wing where lots more of the yellow stuff is visible.
Dave
412 Variant
411 2-door saloon

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broady_6
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Joined: 13th January 2009 - 8:55pm

Re: Foam inside wheel arches

Post by broady_6 » 31st August 2020 - 10:51pm

Very incredibly exceptionally flammable. Waxoyl is useless these days. You're better off with dinitrol, it has rust inhibitors in which waxoyl doesn't seem to have anymore. Sound proofing wise, use some dynamat on thr cabin side of that cavity. It will kill the noise very effectively with out the need to fill the cavity
The sultan of swing

Chino
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Joined: 5th January 2014 - 5:39am
Location: Stockport

Re: Foam inside wheel arches

Post by Chino » 1st September 2020 - 11:24am

Another vote for Dinitrol, waxoyl is old hat these days, rust prevention has moved on somewhat in the last 50years ;) I've been using a lot of dinitrol recently on another project, ML(if going into existing metal with possible rust present) or 3125HS (if going into fresh metal)for cavities, aerosol with the extra long hose they sell. There are some of the treatments which claim to offer noise absorption, I think Dinitrol 4941 does. It's an underbody black treatment applied by aerosol, much easier to use than traditional treatments and leaves a nice level coating, it's what a lot of manufacturers use in the factory now on underbodies and arches etc. As for other methods, Broady is spot on with Dynamat, great stuff if a bit of a faff to apply.

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richtbiscuits
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Joined: 28th February 2015 - 11:25pm

Re: Foam inside wheel arches

Post by richtbiscuits » 1st September 2020 - 3:41pm

I recently cut the quarter panel skin from a 411 variant. That foam extends right round the wheel arch at 2-3 inches thick. I presumed it was sound deadening but it also sticks to the metal pretty well. It's also found it in the cavities at the top of the posts next to the rear hatch at the roof line on variants. I found my rear screen heater wiring stuck fast in it! Perhaps this foam holding water next to metal is the reason the rear arches and roof gutters rot from the inside out!
'72 412 LE Variant
'73 412 LE Variant
'83 1200 Beetle

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937carrera
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Joined: 7th June 2013 - 11:54pm
Location: North Yorkshire

Re: Foam inside wheel arches

Post by 937carrera » 1st September 2020 - 9:06pm

I did a small sill repair to my 412LS. I was very careful to pull the trim and carpet away from the inside. The foam tends to smoulder rather than burst into flames,but I was very very cautious with the MIG and water on hand.

Good to see you still drop in from time to time Chino, though you have been away so long I have managed to catch up on your post count :lol:
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

Chino
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Joined: 5th January 2014 - 5:39am
Location: Stockport

Re: Foam inside wheel arches

Post by Chino » 1st September 2020 - 9:24pm

937carrera wrote:
1st September 2020 - 9:06pm
Good to see you still drop in from time to time Chino, though you have been away so long I have managed to catch up on your post count :lol:
It’s what brought me back, I’d heard the rumours ;)
You never know, might find myself with another type 3 at some point.

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Aaronslimvw
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Re: Foam inside wheel arches

Post by Aaronslimvw » 4th September 2020 - 7:39pm

Roof flashing makes great soundproofing, and a damn sight cheaper than dynamat. Used it on a couple of mini projects in the past and it works a treat.

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sparkywig
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Joined: 28th August 2013 - 12:49pm

Re: Foam inside wheel arches

Post by sparkywig » 4th September 2020 - 8:50pm

Aaronslimvw wrote:
4th September 2020 - 7:39pm
Roof flashing makes great soundproofing, and a damn sight cheaper than dynamat. Used it on a couple of mini projects in the past and it works a treat.
And me, as long as you heat it gently and use a roller.

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