A cane sugar mill is wet, hot and full of fibre

By Johnny Joe, export engineer at Hebei Hongji Shunda Steel Structure Engineering Co., Ltd. · 25 October 2026 · 6 min read

Walk through a cane sugar mill and three things are true at once: everything is warm, everything is damp, and there is fibre in the air.

That combination is what makes a sugar mill a harder building than its structural form suggests. The frame is a conventional industrial frame. The environment is not conventional at all.

Steam and washdown arrive together

Juice heating, evaporation and crystallisation all involve steam, and steam leaks. Washdown adds water at floor level and on equipment. The result is a building that is humid at the top and wet at the bottom, for months at a time.

For a steel envelope, that means the roof underside is a condensing surface and the wall base is an immersion zone. Both are the places where protection fails first, and neither is visible from outside.

Bagasse is fuel, dust and insulation at the same time

Bagasse — the crushed cane fibre — is burned as boiler fuel in most mills, which means the building sits next to a fuel store with a large volume of combustible material.

It also means bagasse dust is everywhere. Dust settles on purlins, in roof profiles and on every horizontal surface, and once it is damp it holds moisture against the steel. The same material that fuels the boiler is quietly shortening the roof.

The combustible dust question also affects the envelope: where relief venting is required, the panels providing it must be fixed to release, and nothing may be hung from them.

The boiler house should not share a frame

It is tempting to build the boiler house and the mill as one structure, because they are adjacent and the drawing is easier. The consequence is that the mill inherits the boiler's fire load, its vibration and its thermal movement.

A wall between them is cheap. A shared frame is not, once the boiler has been in service for a season.

Tall spaces condense on the underside of the roof

Evaporation and crystallisation halls are tall, and tall spaces have a lot of roof to condense on. The drips fall a long way and land on equipment, on product and on people.

Ventilation at high level removes the cause; a liner panel removes the symptom and adds weight to the purlins; a membrane reduces the dripping without stopping the water. Which one is right depends on whether the space can be ventilated at all in the local climate.

The floor carries more than the equipment

Sugar is heavy, and so is wet bagasse. Bins, hoppers and conveyors in a mill carry dense materials on small footprints, and spills are cleaned by hose rather than by shovel.

That combination — point loads plus washdown — puts the slab and its falls under the same pressure as the frame. A floor that drains properly and takes the loads is worth more than a larger span.

What I want before drawings

• The process layout with the vessels, their support points and their temperatures.
• Whether bagasse is stored under cover, and where the boiler is relative to the mill.
• The washdown method and frequency.
• Whether relief venting is expected, and what will be mounted on the walls.
• The ventilation strategy for the tall halls.
• The wind speed for the site in km/h from the applicable local code, not a round number.

Sugar mills are built to run for decades. The buildings that last are the ones where somebody took the steam, the water and the fibre seriously at the same meeting.