Rust Repair Question

[Big G]

Hi Guys

Here is a question for all you panel beating experts out there. I have just started to do some body work on my daughters 55 coupe. It has very little rust and almost zero dings. So around the rear wheel arch there is some of the typical surface rust and some that has chewed up all the metal in that area but hasn't gone as far as getting into the inner skin. I got into it with a sanding disc to reveal the extent of the damage done and it appears not a lot, bonus I thought. Then when I came to clean out the debris between the inner and outer skin I discovered what appears to be a rubberised film between the two. My question is, is this a champion Toyota idea to sound proof the car from road noise or some dodgy buggers idea of rust repair? By filling the rust hole with some spongy goo then bogging over the top of it. If it is genuine and supposed to be there my next question is will it catch fire if I start to weld some small patches in place? The maximum width of the patches would be 15 mm. i don"t want to chop any more sheet metal out than I have to. Has anyone else encountered this before?

[Clapped out]

Wouldn't be the factory seam sealer by any chance? Does it appear that some one may have fixed a rust issue in that area before?

[Big G]

There doesn't appear to be any bog in the area of the rust but I haven't gone too crazy with stripping the paint off in the area as i want to minimise the repaint. It definitely appears to be sandwiched between the inner and outer skins. I have concerns that it may be flammable. I don t want to burn her pride and joy to the ground before she gets it on the road.

[oh what a nissan feeling!]

It sounds like factory sealer, it does catch on fire with enough heat but not badly. I usually blow it out and keep welding, it doesnt really like to burn and goes out easily.