Who invented Jarvising?

Since before the second world war, my old maternal grandmother used to ask my grandad Ernie "what have you been doing all day in that allotment [or shed/cellar/back yard]?"
"Jarvising" he would say. That is all they got out of him - the equivalent of the Yorkshire saying "making a wimwam for ducks to perk on". I cannot find the expression in Notts dialect sites so he possibly made it up, or maybe it was an expression from his work. Ernie was an engineering fitter in Hooton's Nottingham lace factory, or rather he was when he had the work, which was scarce in the 1930's.
Since my wife heard the story from my mother, she has described my messing about in sheds as "Jarvising".