Ballarat company Hearty Homes construction manager and site foreman George Danciu said vandals had smashed fly screens, damaged plaster, smashed lights, spread paint and attempted to flood properties.

"I feel very angry," he said.

"The damage has been getting worse and worse."

Mr Danciu said the vandalism began about a week and a half ago. He arrived on-site where Hearty Homes is building 15 units as part of the new Pennyweight Gully Estate on Joseph Street in Canadian.

He found offenders had forced their way into the house, smashed the fly screen and damaged the plaster and a toilet.

Mr Danciu said he arrived on-site again one morning last week to find a different unit had been targeted and the offenders had smashed all the lights in the house and thrown tile glue on the floor.

A brick had been thrown through the door of one of the other units.

On Sunday morning a concreter arrived to find the door to one of the units open and mud all over the carpet.

This week Mr Danciu arrived on-site to find the offenders had forced a window to another unit, broken the pipe in the toilet and tried to flood the house.

He went for a drive around houses nearby under construction by other development companies and found eight had their fly screens kicked in.

"One was nearly ready to hand over to the owners," he said.

"They broke in, flooded the kitchen, there was water everywhere. I turned off the main water and told the supervisor.

"Next to him it was another Melbourne builder and it looked like the painter had just finished painting. They threw the buckets with the paint on the floor and smashed all the walls there."

Mr Danciu said the vandalism would delay the completion of the properties which was frustrating for builders who were working under high pressure.

"It creates extra work," he said.

"Every builder has insurance, but there are delays because you have to order again, new doors and it is another couple of weeks for the doors, getting the plasterer to patch up everything, sand it fix it.

"The painter has to do repainting, clean the carpet or maybe have to replace the carpet. It delays the houses.

"I feel very angry. Why do they come into my house? I am supervising here, I am in charge of it."

Mr Danciu said it also created extra work to prevent break-ins and he felt stressed every day on-site.

"Every night before I go I have to spend extra time, it makes it hard for the supervisor," he said.

"You have to double check all the windows and the doors that are locked and I put timber under the windows so they can't open it."

Mr Danciu said he had never seen properties targeted so frequently in his lifetime of work as a builder.

"I have been in building nearly all my life, you can have it once at one house where it is broken and appliances are stolen. But here they come back so often," he said.

"The last week they have been back nearly every second night. I have never seen anything like this before."

Mr Danciu said he was also worried for residents who had already moved into properties in the new estate as one said she felt scared when she heard someone trying to open her window and shining a torch in at night.

"We want them to stop. It is not good for the building industry," he said.

Ballarat Criminal Investigation Unit confirmed it is investigating criminal damage to 12 to 15 houses in the new Pennyweight Gully Estate on Joseph Street in Canadian.

There are a total of 22 homes to be completed in the new estate.

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