FOND DU LAC, Wis. — Mercury Marine has begun a $20 million expansion of two of its Fond du Lac plants, saying there has been greater demand for its outboard engines amid the slow rebound of the boating industry following some tough years.

The company has begun constructing the expansions, which will add a total of 38,000 square feet of manufacturing space to the 1.5 million it already has in the city.

"This is another statement of the success that we have at Mercury Marine and our continued commitment to the community and employees in Fond du Lac," President Mark Schwabero said Thursday, when the official groundbreaking was held.

Construction is expected to be completed by December, with some equipment installed this year and more coming in the following two years, according to The Reporter Media ( ).

Mercury Marine is adding 20,000 square feet at one plant to house horizontal machining equipment and 18,000 square feet at a casting facility to house high-pressure die-cast machines.

The company bills itself as the world's leading manufacturer of recreational marine propulsion engines.

Fond du Lac County Executive Allen Buechel said Mercury Marine is doing better than expected just four years after seeking worker concessions and financial help from the city, county and state. He said the expansion will help the area's construction industry and provide additional manufacturing jobs.

Mercury Marine employs 2,900 people in Fond du Lac, which is up from the 1,600 people it employed in 2009 when it was exploring leaving Wisconsin and consolidating its operations in Oklahoma. Union concessions and government support kept the company in Wisconsin.

The company is due to pay off a $50 million loan from the county by 2021, when a half-cent county sales tax to help pay for the financing of Mercury's loans also ends. The company is paying for the expansion projects itself, without government aid.

With the boating industry growing again, albeit slowly, there has been greater demand for Mercury Marine's 75-horsepower and higher outboard engines, Schwabero said.

John Pfeifer, vice president of global operations, added that the company also does more commercial and government work than people realize.