Bad experience with Halfords Exhaust repair putty

[hightower]

I brought a new tail pipe for the exhaust as it has a few holes on it but could only remove 1 of the 3 bolts as the original tailpipe is shaped so that you cant get a socket on 2 of them and couldnt get enough leverage with a spanner to shift them so i brought some Halfords exhaust repair putty (was 50p cheaper than gun gum) as a temporary measure for now. Before i flew out to Spain two weeks ago i slapped some of the paste over the offending holes and left it to dry and cure for a week while i was away.When i got back last Thursday we had to use the van for a trip to Asda due to my fiat scudo refusing to start, on my return i noticed the paste had bubbled up badly so i slapped a bit more on for our trip to Vanfest.

Well driving in convoy with a split and bay to vanfest i noticed my van was a bit sluggish and was having trouble keeping up with them , also when you put your foot down there was a strange loud whistling/vacuum noise. Got to vanfest and thought maybe the repair paste had bubbled up inside the tailpipe, went to investigate with a tent peg and found most of the putty had cracked and fallen off the tailpipe and also i managed to chip out a walnut sized lump of repair putty from inside the tailpipe, it had bubbled up like honeycomb and was severely restricting the exhaust (try sticking a walnut in your tailpipe to see what i mean), needless to say i was back to normal full power on the way home, definitely wont be using that stuff again.
I have used the Holts Gun Gum before and never experienced this before, definitely will be sticking to known brands in the future.

[Steve T]

In the past by experiment, for sealing a split along a seam on an exhaust system silencer box I used "I cant believe its not nails" mastic. Also gripfill works. It passed an MOT with it on, would not have passed with it blowing out the seam. It does not cure a buggered exhaust as if it is the state of decay it will need to be replaced, however it buys you time.