Marion and Kevin McLeod fulfilled a long-term dream last week when they unveiled Ace of Steaks, a new restaurant on the Princes Highway in Dapto.

The couple were six days into the venture when the arsonists struck early on Sunday morning, causing thousands of dollars of damage to the building.

"We came in on Sunday and the shop had been broken into and burned - it took a lot of effort to clean it up," Mrs McLeod said.

"I was devastated, I nearly cried. We worked so hard to get the restaurant open in such a short amount of time and we're all in total shock.

"All our staff and friends turned up yesterday and they're all going to be back here helping us, and we've had a lot of support from other people offering help."

According to Mrs McLeod, the vandals gained entry to the building via a ground-level door, before starting the fire in the second-level ceiling and dousing a nearby storeroom and stairwell with a liquid cocktail. However, the mix wasn't flammable enough and the fire subsequently died.

The restaurant is part of a larger building which houses residential and commercial tenants, but none of those were affected by the fire.

The Ace of Steaks portion of the building was formerly a Mexican restaurant which had been in business for about 20 years without incident.

Because the fire hadn't caused major structural damage, Mrs McLeod was hopeful of reopening before Christmas.

"We're going to need to repaint again, the ceiling needs replacing in parts and the carpet will need to be replaced - we've run into thousands of dollars in repair bills," she said.

"But this is what we've always wanted to do so we're not letting whoever did this get the better of us.

"We're very lucky that the fire has actually burnt itself out."

Lake Illawarra detectives are continuing their investigations.