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Furniture fit for bathrooms
Bathroom furniture needs to perform in a particularly hostile environment.
Image © Porcelanosa
Bathrooms are hot and steamy places and this means that furniture and fitments need to be durable and able to stand up to high humidity, water-splashes and some potentially aggressive cleaning materials.
What happens to wood in bathrooms?
Wood products in the bathroom absorb moisture from the air and hence might swell and distort. Lacquered or painted items might suffer from surface cracks caused by timber movement. Wood expands in size as it absorbs moisture. It is this sponge effect which makes drawers and doors stick when the moisture content increases. Expanding timber could also be the cause of splits in cabinet tops and shelves. Joints, too, might open up when timber absorbs moisture. Gaps often become more noticeable in mitred joints.
How can wood be used successfully in bathrooms?
There are a number of strategies available to the designer and furniture manufacturer. First choose a timber that has low movement characteristics, (for example, mahogany is a low movement timber and beech is a high movement timber). This way, if there is any movement, the visual effect will be small in a low movement timber. See box 1 for further information.
Box 1: Movement characteristics
The movement of timbers in service is based on the sum of the tangential and radial
movements corresponding to a change in humidity conditions from 90 per cent to 60 per cent relative humidity (RH).
Small movement is classified as under 3 per cent.
Medium movement is classified as 3 per cent to 4.5 per cent.
Large movement is classified as over 4.5 per cent.
Some common timbers and their movement classification:
- beech large
- cherry medium
- iroko small
- oak medium
- mahogany small
- ramin large
- teak small
- utile medium
- walnut medium
Secondly, choose a method of construction where flush joints are avoided and where there is an opportunity for movement to take place without stressing glue lines. Thirdly, ensure moisture-resistant adhesives are used throughout. Fourthly, select a lacquer or paint that has good flexibility to cope with any small movements of the underlying wooden substrate. Usually if the cracks in the lacquer follow the grain of the wood then the cause is most probably due to movement of the timber. If the cracks in the lacquer are random in both direction and shape the cause is almost certainly due to inflexibility in the lacquer.
What about metal items?
Some metal items may tarnish or corrode in humid bathrooms and care should be taken to select hardware items that have adequate protection via powder coatings, plating or lacquered finishes.
How can we predict performance in bathrooms?
The performance in use of bathroom (and shower room) products can best be predicted by using a chamber with a constant high humidity. SATRA uses a large chamber set at 85 per cent RH and 25°C to evaluate bathroom furniture and accessories. This constant high humidity atmosphere allows items to be observed over a period of several weeks and for signs of deterioration to be identified. Careful measurements of product dimensions are taken at regular intervals to plot any change. The surfaces of furniture are examined for the emergence of cracks or fissures, which indicate excessive movement and which could result in a customer complaint.
Image © Porcelanosa
Box 2: Problems identified with bathroom furniture
Typical examples of problems with wooden bathroom cabinets and accessories such as towel rails, shelves, racks and mirror frames include:
- drawers that stick due to expansion of the timber
- painted surface that cracks due to movement of the substrate and inflexibility of the coating
- glued joints in cabinet tops that open due to moisture pick-up and swelling of the wood
- lacquer finishes that craze due to poor resistance to humidity change
- hinges, catches and handles that tarnish due to exposure to high humidity
- surfaces of marble that mark with the application of soaps and cleaning agents
- finishes that mark with the application of cosmetics
- wood particle board swelling due to moisture pick-up.
The performance of surface finishes in bathroom environments is assessed using a number of tests which examine their ability to withstand the rigours of day-to-day use.
The quality of surface finishes is usually assessed in relation to three criteria:
- mechanical damage, for example resistance to abrasion, impacts and scratching
- climatic influences, for example fading due to light, and the effects of temperature and humidity
- chemical resistance, for example resistance to oils, acids, bleaches and foodstuffs.
Spillages and accidents with cosmetics and cleaning materials might be expected in any bathroom environment. Suppliers of furniture products, especially those made from wood, need to be careful with product information to help the consumer to choose the appropriate cleaning materials and to flag-up the risks of spilling cleaning materials such as bleach. The consequences of spilling cosmetics such as nail varnish, nail varnish remover and shampoo should be highlighted and tips on removal and cleaning given.
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