QuikSteel - Am I Doing It Wrong?

[ShaunTheSheep]

I had an oil cooler line corrode to the point that it started dripping occasionally. I wanted a temporary repair until replacement lines could be made up and sent over so i decided to try QuikSteel - http://www.kalimex.co.uk/our-products/quiksteel

T'internet reckons this stuff is the best thing since sliced bread. I followed the instructions:

• drained the oil out the corroded section of pipe
• sanded off the worst of the corrosion, there was no bright shiny metal to rub back to though so i just rubbed until there were no loose bits
• I wiped the pipe over thoroughly with IPA
• I mixed the putty until it was all one colour and warm to the touch
• I applied it about 2-3mm thick all around the pipe and about 3 inches either side of the hole - 6 inches of this stuff. So that it could bond to non-rusted pipe.
• Left it 3 days to cure

I tested it at idle, all good, let the engine warm up, still good. Tried it at higher revs, still good. Took it for a gentle run, still good. Give it a bit of welly and all of a sudden i have oil pouring out. Wayyy faster than before the repair!

What gives? Should i have put it on thicker? Heated it to cure it?