Kelcroft E&M Limited John Herbert
unit A10 Kowloon Bay Hong Kong
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Vinyl Wallpaper, Air Conditioned Room, Best Swipe Left

Lining the external wall surface of an air conditioned room using vinyl wallpaper causes mould, and with it, the unwelcome effects on the health of occupants.

Vinyl wall coverings, and materials with the same phyiscal properties, stop the natural moisture flow, because vinyl wallpaper is a vapour retarder. This causes moisture to accumulate in the building structure behind the wallpaper and mould is the inevitable result.

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If the external wall is lined with any type vapour retarder, including mirror, whiteboard, plastic laminate, plastic paint, or perspex/acrylic the outcome is the same, the flow of moisture is halted, moisture accumlates and mould is the result.

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Modern furniture can be problematic too, often it is constructed with plywood or MDF and finished with plastic laminate, a vapour retarder, that traps moisture and causes mould.

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Why does lining the external wall of an air conditioned room with vinyl wallpaper cause mould?

This is natural phenomena, the air vapour pressure of outdoor air in Hong Kong (and tropical regions) is significantly higher than the air vapour pressure indoors, that pressure difference drives that moisture from high pressure outdoors into the air conditioned space having a lower pressure.

vinyl wallpaper mould, air conditioning mold

In air conditioned rooms without a vapour retarder, the moisture enters the air conditioned room and the ventilation system transfers the moisture in the air to the air conditioning unit where it is condensed, and this prevents moisture accumulating in the building fabric.

Obviously, in a building with rooms using natural ventilation, they contain outdoor air with the same air vapour pressure as outside air, therefore moisture diffusion does not occur.

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However, if the room space has any void space, isolated from the room ventilation, moisture will accumulate in any unvented voids, once again causing mould.

Therefore, its important to understand the moisture modes, air movement and diffusion are the vectors for transporting moisture and good ventilation throughout is the best solution.

Reference: Moisture Control Guidance for Building Design, Construction and Maintenance, page 18 (

About the Author

John Herbert is a veteran chief engineer with more than 30 years international engineering experience, educated in the United Kingdom, he has worked in the United Kingdom and then across Asia for more than two decades engaged by international and local companies. He is a Hong Kong Registered Energy Assessor (REA), a BEAM Professional, and stationed in Hong Kong.

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