Of all the moisture damage we see, the single most preventable category is wrapped stacks that were put away wet. It happens on a Friday, it is discovered on a Monday, and by then the bloom is established.
The mechanism
Mould needs four things: a food source, oxygen, a temperature roughly between 4 and 38 °C, and moisture above about 20% in the wood. Wood is the food source and you cannot remove oxygen or temperature from a warehouse. Moisture is the only variable you control.
Stretch film is a vapour barrier. Water that is inside the wrap when you apply it stays inside the wrap. It cannot evaporate, it redistributes across every surface it touches, and it sits in the dark at a convenient temperature. That is not storage, it is incubation.
Where the water comes from
Rarely rain, which people expect. Usually condensation. A cold platform brought into warm humid air collects water on every surface — the same reason a glass sweats. Overnight dew on an outdoor stack does the same. A wash-down nearby does it. A concrete floor wicks moisture upward into the bottom course of a stack sitting directly on it.
The rules that fix almost all of it
- Do not wrap damp. If a stack comes in wet or cold, break it, let it equalise, and wrap it when it is dry. An afternoon of patience beats a pallet of scrap.
- Store off the ground. Dunnage, a sacrificial pallet, anything. Concrete wicks and the bottom course pays for it.
- Give airflow on at least two sides. A stack jammed into a corner cannot dry.
- Rotate stock properly. Mould is as much a time problem as a water problem; genuine FIFO starves it.
- Wrap for transport, not for storage. If a stack is going to sit for weeks, it does not need film.
Telling the three discolourations apart
Surface mould wipes or brushes off and leaves sound wood underneath. Cosmetic, and for food programmes it can be kiln-dried out. Blue stain is a fungus that penetrates and discolours without meaningfully weakening the wood — ugly, structurally irrelevant, and frequently rejected by buyers who do not know the difference. Decay is soft, punky, crumbling wood that gives under a thumbnail. That platform is finished; it goes to the grinder and becomes mulch.
If it has already bloomed
Separate it immediately so it does not seed the stacks around it. Assess which of the three you have. Surface mould on a structurally sound platform is usually salvageable and we can kiln it if your programme requires. Decay is not, and pretending otherwise just moves the problem to your customer's dock.
Why a cold platform is the dangerous one
Condensation forms when a surface is colder than the dew point of the surrounding air. A stack that has sat on a trailer overnight in February and comes into a heated warehouse at sixty percent relative humidity will wet itself thoroughly within minutes — not from any water source, simply from the air.
That is why the worst mould incidents cluster in spring and autumn rather than in winter. It is not rain; it is temperature differential. A platform brought in cold and wrapped immediately has a film of water sealed against it, in the dark, at a temperature fungi find agreeable.
The three-day rule we give customers
Any stack arriving cold or damp gets broken and left to equalise for a minimum of a day, ideally three, before it goes under film or into a tight storage location. It is an annoying rule because it requires floor space and patience on a day when you have neither. It is also the single intervention that eliminates most of the moisture complaints we receive.
What to look for on a Monday morning
- Condensation on the inside of the film. Visible water droplets mean you have a greenhouse. Unwrap now, not later.
- A darker band on the bottom course. Wicking from concrete. The fix is dunnage, permanently.
- Fuzzy growth, grey-green or white. Surface mould. Separate the stack immediately so it does not seed its neighbours.
- Even blue-grey discolouration penetrating the board. Blue stain. Structurally irrelevant, cosmetically fatal to a retail-facing programme, and frequently rejected by buyers who do not know the difference.
- Soft wood that gives under a thumbnail. Decay. That platform is finished and pretending otherwise just relocates the problem.
The storage specification that prevents all of it
Off the ground on dunnage. Under cover. Airflow on at least two faces. Unwrapped if it is not moving this week. Genuine FIFO so nothing stands long enough to matter. That is five lines, none of them require capital, and together they are worth more than any product we sell.
If you cannot manage covered storage, tell us and we will hold buffer stock here against your spec instead. Our shed is already built.
Dale, repair lead · Pallets Recycle, 1113 Ingram Ave, Richmond VA · published October 8, 2024 · 812 words. Corrections welcome — tell us if we have this wrong.