Last weekend the church in central Vienna was pelted with paint bombs and the exterior was smeared with anarchist symbols and left-wing slogans such as "resistance follows repression". Several statues on the outside of the church were also daubed with paint.
The facade of the church is being cleaned and the two damaged statues are being restored. The work will take about two weeks and cost around 13,000 euros.
"We think it has not affected the colour of the exterior, thank goodness," said Markus Schindler of the Green Concept Cleaning company.
The cost of the clean-up will be covered by money earned from entrance fees paid by visitors to the church.
The perpetrators have not been identified. John Pasquali, from the group Friends and Patrons of Karlskirche told Der Kurier paper that he was shocked that anyone would think of doing such a thing to an important part of the city's cultural heritage.
The attack on the Karlskirche is not an isolated incident. Last weekend there was an arson attack on a church in Bregenz, on Lake Constance, in which the entrance to the Mariahilf church was damaged.
A 52-year-old woman discovered the fire and with the help of a passer-by she tried to extinguish it. She had to be treated for suspected smoke inhalation in hospital.
In March a man was arrested in Vienna for committing various acts of vandalism on churches. He confessed to six acts, saying he was on a "divine mission".