The controversial graffiti of a silhouetted boy and a girl arching their arms to form a heart will soon disappear from the City Gate entrance as a cleaning team went on site last night.

The cleaning works will run up a bill of €4,000, “excluding VAT”, according to Chris Paris, CEO of the Grand Harbour Regeneration Corporation.

The major cost lies in the equipment used to remove the graffiti at its particular height, he said – although last night the start of cleaning works were delayed when the cherry picker appeared to malfunction.

A specific type of cherry picker is being used to ensure the safety of the workers. The cleaning process is expected to take between one and three days.

“The perpetrator must have been quite intrepid – he balanced on the tiny ledge overlooking the large drop down to the ditch. We carried out a risk assessment as we didn’t want to expose the workers to the risk,” said Mr Paris.

The graffiti appeared on the left side of City Gate overlooking the ditch in the early hours on August 29.

The police are still looking for the perpetrator, who was spotted spraying the graffiti by a police patrol at about 4am.

The incident stirred a debate as the metre-high graffiti was sprayed on a prominent slab that forms part of the €80 million national project lauded by some and criticised by others.

The spray can used on the graffiti was left behind as the perpetrator made his escape from a police patrol. It was handed over to Hal Mann, which was tasked with solving the problem.

Hal Mann architect Hugh Vella told Times of Malta the team conducted three trials: one on the spraying material, another on the surface finish and another to test the reaction of the stone.

The stone at the Valletta entrance is Upper Coralline Limestone (Qawwi ta’ Fuq) cut from a Gozo quarry.

The next phase centred on exploring different ways of removing the spray. Solvent was tested but a technique known as water blasting, together with mechanical cleaning was deemed most appropriate.

The graffiti is being washed with high high pressure together with an additive. Then the entire slab will be scrubbed intensely using special equipment.