"PARALLEL OF LIFE AND ART": The re-painted bus shelter yesterday. Below, the artistically inclined add their own touches to the shelter.

A controversial artwork has become the victim of a reverse-graffiti attack in which the Hamilton Tag Busters squad swooped on the piece and administered a re-spray.

The bus shelter, entitled "Parallel of Life and Art", by Auckland artists Michael Parr and Blaine Western won this year's National Contemporary Art Award, hosted by Waikato Museum.

The drab, cream-coloured and utilitarian structure was awarded top honours by judge and curator Caterina Riva last month.

Ms Riva at the time described the $15,000 winner as "not just a bus stop", and seemed to suggest the public would be welcome to add their own daubs of paint to the piece.

"I think that's the negotiation - they're [the artists] actually quite happy for people to use it. Their job is sort of finished once they put it up there, then it's for the people to do what they want with it - to use it, abuse it," Ms Riva said.

And Hamilton's artistically inclined residents - many of them children - took her at her word.

Simple works of graffiti were left on the shelter, among them a quote from US author Kurt Vonnegut.

The piece got another splash of paint at the weekend, that included images of colourful flowers, hand prints, stick figures and love hearts.

But it was all too much for the council's graffiti removal squad, who painted it over on Wednesday after permission was granted from the artists.

The museum has now vowed to remove all future bits of unauthorised graffiti and tags immediately.

Museum marketing manager Louise Belay said there had been some confusion over whether the artists had initially welcomed the public to paint the shelter, despite what Ms Riva had said.

"I don't think she [Ms Riva] intended for it to be understood like that, I really don't, because when she read the story she emailed us and was concerned that it was giving the wrong message," Miss Belay said.

An awkward situation had developed as the judge's comments "have inspired people to think it's okay to come and paint graffiti on an art entry".

"Whether you see it as an art entry or a bus shelter, it's really not okay to come and deface it."

Had they been asked, both the museum and Hamilton City Council would have had a different message for the public, Miss Belay said.

"The original message that we would have given out [would have been] that the artists were interested in the interaction with the public and the bus shelter."

Earlier items of graffiti may have been left on the shelter, but the weekend's public paint job was too much, Miss Belay said.

"What happened was we had a situation where a group of people arrived quite late at the museum on Saturday and ‘decorated' it and this also extended to paint going onto the tiles, some paint going up the side of our water feature and the signage was spray-painted blue."

Auckland art critic Hamish Keith was unsurprised to hear the work had been hit by paint-wielding passers-by.

"There is nothing about that that made it any different, that told a passer-by with a spray can that it was anything else other than a bus shelter," he said.

"It's not a bus shelter, it's an idea, and I think it's a very ordinary idea to tell you the truth. It is an ordinary object with ordinary paint on it and it got treated by passers-by as an ordinary thing," Mr Keith said.