David Cannon, 66, blasted the slurry over the branch, in Newcastle upon Tyne, in a gesture which led to a two-week clean-up by stonemasons.
Cannon had a five-year battle with the bank, which he claimed had mismanaged his accounts, costing him more than pounds 100,000 and forcing him to sell his prize-winning herd of Ayrshire cows at his farm, near Ponteland, Northumberland.
After he started spraying the building, in Moseley Street, Newcastle, passers-by had to dive for cover.
Bank manager Alan Bell told Newcastle magistrates: "There was a large deposit of manure sprayed up the walls to considerable height and lying in a heap outside the door.
"We had to have scaffolding erected and the stonework professionally cleaned because the matter had leaked into the sandstone. The effluent was too deep to walk into the bank unless you had waders on."
Cannon was convicted of criminal damage but was given a conditional discharge by magistrates, who ordered him to pay pounds 2,000 compensation, although NatWest had claimed pounds 4,500.
The farmer earlier told the court he did not know the bank branch was a listed building.
He added: "Nobody knows the frustration we've had because of the bank. There's plenty of people who would have ended up in the nuthouse or been driven to suicide".
Three years ago, Cannon was ordered to pay pounds 1,138 compensation to Castle Morpeth Council, Northumberland, for spraying their offices with slurry after being refused planning permission to build a bungalow.
Cannon, who is suing NatWest through the civil courts, alleging negligence over the handling of his affairs, said after yesterday's hearing: "I have no regrets about what I did. After all, they dropped me in the shit.
"I would do the same every morning if I could keep myself out of jail. It doesn't take any bottle to drive a tractor into town and start the muckspreader. "I was driven to it by sheer frustration. It was a case of the little man being hammered by a big institution and I couldn't take any more."Reuse content