Pittsburgh mechanical contractor Limbach Holdings LLC says it is going public in a $97-million merger with a special-purpose acquisition company that trades on the NASDAQ exchange. Limbach would become its operating company when the deal finishes, set for summer. Industry firms Primoris, Great Lakes Dredge & Dock and Hill International used the same approach. Limbach says it had $331 million in 2015 revenue, up 12% over the previous year, and net earnings of $13 million. Sources say the firm, which notes “continued growth” in high-margin service and maintenance areas, sees strength in its new corporate governance rules. Charlie Bacon will continue as CEO. Conglomerates Enron and Vivendi previously owned Limbach. Private-equity firm FdG maintains a 30% stake in the contractor.