The early evening blaze began in a stock of roundwood, but was not suspicious, the Scottish Fire and Rescue Service (SFRS) said. Much of the site was affected by smoke.
The company confirmed that no-one was injured and staff were working next morning. A statement said the vast majority of operations was unaffected.
At the height of the blaze six fire appliances were at the scene and 20 firefighters fought for two hours to get it under control.
"This was a substantial fire and both the retained and whole-time crews worked extremely well to ensure the incident was brought to a safe conclusion," said Phil Green, the senior SFRS officer at the incident.
"The building’s roof was unstable and the presence of underfloor hydraulic piping meant the best course of action was to operate externally," he added. "A ground monitor and three further main water jets were used to extinguish the flames from outside the premises."
