I spotted a bad patch of underseal on the off side right rear sill of my Octavia. I had a look and peeled it back as it was not stuck on anyway, I was quite surprised to find this -

The question is what should I do next? I have sanded the rust down so it is now back to smooth clean metal and was debating about primer / undersealing it myself, although I recalled these are covered by a 10 year rust warranty. The trouble was it took 4 months to sort out the warranty claim with Skoda last time for the boot! I am worried if I leave this too long it will become worse and then need welding.

I suspect that because you've had a go at it, you've invalidated the bodywork warranty.

I'd expand the area a bit just till you reach none rusty metal, give it a going over with a wire brush and apply some rust stabiliser/converter asap to stop the rot…

Then you could cover this with some Stonechip shield

And then finish with top coat, or do stone chip on both sills in stone chip so they match... depends how fussy you are about the finish.

I've found a few small spots behind my wheel arch liners and am gonna go at them with KRUST and some Stonechip shield or underbody seal.

Cheers for the reply Rich. Well I felt it should be protected as well and luckily from doing some work to the MX5 over the winter I had some Tetro Seal underseal to put on. Nice thick black stuff! My plan is to do another coat tomorrow evening providing the weather holds up. I also have two aerosol cans of the correct car paint colour, so considering the sill has taken such a battering Im going to spray the whole length I think! :yes: There are a few other chips and blemishes too.

I have done one arch liner so far, planning to replace the o/s rear due to damage and then check the two fronts. Luckily the one I did didn't have any rust behind it.

Here are some pics -

Cleaned and ready to paint -

Painted -

Unfortunately the other side was quite bad too -

I did the same on mine where it had been jacked badly in the past.

I was going to say, I imagine it has been jacked on the sills, they have bent over and then been bent back and that has caused the underseal to become loose, and then that allows the dampness in and for the rust to start.....

doing mine again this weekend, and the whole underside of the car too, ****ty uk weather

Yeah the weather definitley doesn't help. :( Im sure last winter helped with creating the rust! Im just glad I spotted it!