Condensation, rust and a Northern Rivers wet season

Complaint one: "it is leaking, there is water on my gear"

Nine times out of ten it is not leaking. It is condensation, and it is the single most misunderstood thing about steel boxes in a subtropical climate.

Here is the mechanism. Warm, humid air gets into the container — every time the doors are opened, and there is plenty of it here. Overnight the steel roof radiates heat to a clear sky and cools below the dew point of the air inside. Moisture comes out of that air onto the underside of the roof, forms droplets, and falls on whatever is below. People find water on the top of a stack of boxes, look up, see a wet ceiling and reasonably conclude the roof leaks.

The tell is where the water is. A leak makes a mark at a specific point and runs down from it, usually at a seam, a repair or a corner. Condensation is spread evenly across the whole ceiling and is worst on the mornings after the clearest, coolest nights.

What actually fixes it

• Vents. Passive vents in the side walls, high one end and low the other, let the air move rather than sit. Cheap, no moving parts, and the single most effective thing you can do. Ask for them when you order rather than retrofitting later.
• Get things off the floor. Pallets or bearers under anything stored directly on the marine ply. It stops moisture wicking up into cardboard and fabric and it lets air circulate underneath.
• Desiccant for the small stuff. Hanging moisture absorbers are genuinely useful in a container storing documents, tools or electronics. They are not a substitute for ventilation.
• Insulation if it matters. For anything genuinely moisture-sensitive, or for any conversion, insulating the roof stops the surface getting cold enough to condense at all. That is the proper fix and it is worth deciding before purchase, because it is also an argument for buying a high cube.
• Do not park it under a tree thinking it will help. It will not help the condensation and it will drop leaf litter and sap on the roof, hold moisture against the paint and give you a rust problem instead.

Complaint two: "it has gone rusty faster than I expected"

This is almost always a coastal container. From Evans Head north through Ballina, Lennox, Byron and Brunswick you are in constant salt air, and salt is relentless on any exposed metal.

The important point is that salt does not eat through good paint. It gets in at damage — a scratch from a forklift tine, a chip from a strap, a repair that was never painted properly, a weld that was left bare. On an inland block at Casino or Kyogle those spots might sit for years looking much the same. Three streets back from the beach they will show rust within a season.

What actually fixes it

• Buy the right grade for the location. On a coastal block, cargo-worthy or new. An as-is unit's existing weak points are exactly where salt will start.
• Touch up damage when it happens. A wire brush, a rust converter and a tin of enamel. Fifteen minutes twice a year is the whole maintenance program.
• Get it up off the ground. Pads or sleepers under the corner castings so the underside can dry and the floor edges are not sitting in damp grass. This matters as much for rust as it does for keeping the box level.
• Let water off the roof. A container roof has a slight camber and it works, unless leaf litter dams it. Sweep it occasionally if it is under anything.
• Watch the door end. Set the container with a fall away from the doors so the threshold is not standing in water after ordinary rain. The bottom edge of the door aperture and the floor edge behind it are where a container usually starts to go.

The wet season, honestly

A good cargo-worthy container will keep a Northern Rivers wet season out of your gear — that is exactly what wind and watertight means, and it is a real claim about rain arriving from above. What it will not do is keep out water that rises from below, and it will not stop the air inside it from being humid. Ventilation, pads and fifteen minutes of maintenance twice a year handle everything else.

If you want a container specified properly for where it is actually going, ring 02 6622 1322 and say where that is. Vents, insulation and grade are much cheaper decisions made before delivery than after.