A fire burnt through mulch at Canberra Sand and Gravel's Parkwood Road facility on Wednesday, the second fire at the business in less than a month.

Firefighters took most of the day to extinguish the fire, which was caused by spontaneous combustion.

The fire measured 50 metres by 50 metres and nine fire tankers were called to break up the mulch.

About 90 per cent of the fire had been extinguished by 5.30pm. Crews stayed on through the evening to put the rest of the fire out.

They were called out to the facility at 6.54am.

The Canberra Sand and Gravel facility was hit by another fire, which also started in a mulch pile, on November 16. That fire also took hours to extinguish.