They do make a product caled welding backup tape.
It's a 3M product.
Do the research it's made for just the situations you mention.

Stan Wilder
www.engineceramics.com
----- Original Message -----
From: "John Harvey" <gti_02@YAHOO.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Saturday, July 31, 2004 3:03 PM
Subject: Welding Question

> In  the near future I'm going to be welding in some
> replacement sheet metal on a project car.  I'm
> concerned the the backside of the repair will rust
> (esp. the welds) since I can't physically get at it to
> paint it.  Is there a product that can be applied to
> the areas of concern prior to welding that will
> prevent rust?  Seems far fetched to me.
>
> Should I just drill a tiny access hole and spray in a
> bunch of rust prevention stuff after welding?   I'm
> imagining oily, waxy stuff in and aerosol spray can.
>
> Clueless in Corvallis, John
>
> =====
> '76 2002
> '85 Vanagon
> '91 GTi
>
>
>
>
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