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24 June 2019

Lighting and Installation Considerations for a Quality Plasterboard Finish

GIB The Block 260

No matter how smooth wall and ceiling linings appear, they will never be 100% physically flat and blemish-free. This applies to any interior surface comprising jointed sheet type material including fibrous plaster, plywood, MDF, plasterboard and even glass. All of these substrate materials contain physical deviations or minor blemishes.

Although it is impossible to get a perfectly physically flat or blemish-free interior surface, it is possible to achieve ‘the appearance’ of blemish-free flatness.

The below design and lighting considerations can make a big difference in the quality of your plasterboard finish.

Design and installation considerations:

Specify metal ceiling battens

The use of metal ceiling battens is recommended on all ceilings rather than timber ceiling battens. As metal ceiling battens hold no moisture, they will not bend, twist or warp and therefore help to achieve and maintain a straight and true ceiling.

Opt for 13mm plasterboard ceiling linings

We recommend specifying 13mm plasterboard on all ceilings throughout your project. A thicker, stronger 13mm plasterboard gives you extra rigidity to help fight the effects of gravity and structural movement.

If 10mm plasterboard is chosen, then it must be fixed to battens spaced at maximum 450mm centres on ceilings. However, the extra rigidity of 13mm plasterboard enables you to have ceiling battens spaced up to 600mm apart. As there are fewer ceiling battens, fewer fasteners are required, resulting in fewer points where imperfections could be visible.

Use horizontal fixing to reduce shadowing

Any imperfections will be most noticeable at the joints of wall linings so it pays to keep these joints to a minimum. Fixing plasterboard sheets horizontally instead of vertically on walls reduces the number of joints, helping to achieve a more uniform appearance.

Horizontal fixing also means that light from adjacent windows shines along the joint, thus reducing the “shadowing” effect that is sometimes noticeable with vertical fixing. With horizontal fixing, there is only one joint which is below eye level.

Ensure all framing is dry and straight

The final finish quality of a plasterboard wall or ceiling is heavily influenced by the quality of the framing to which the plasterboard is fixed. If framing is not straight and aligned, it will be reflected in the finished appearance of the wall or ceiling.

Any timber framing must also be dry prior to the plasterboard being installed, otherwise, the framing may shrink or twist as it dries and cause cracks, nail pops and other problems in plasterboard linings. Alternatively, steel framing can be used.

Lighting considerations:

Minimise critical lighting

Lighting design is vitally important in minimising the visibility of any minor imperfections because it’s the lighting conditions that create the “shadow” that makes any imperfection visible. Lighting design will either accentuate or diminish the visibility of any imperfections.

When light strikes a surface at a shallow angle it tends to greatly exaggerate any surface irregularities and this is termed “critical lighting”. Critical lighting should be avoided where possible. If it cannot be avoided it needs to be accepted that some imperfections may be visible under extreme lighting conditions. A degree of agreement, co-operation, acceptance and tolerance is required between parties.

However, when the angle of light is more or less at right angles to a surface, imperfections are less obvious and this is termed “noncritical lighting”.

  • Recessed downlights and light shades: Incorporating recessed downlights or light shades help to channel light downwards and reduce the amount of glancing or critical light.
  • Window positioning and shades: Avoid positioning narrow windows hard up against the end of a wall or ceiling, particularly on long walls or ceilings at the end of a room or hallway. Making a window wider and placing it away from the room corner should reduce the critical lighting effect. Try not to take windows right up to ceiling level. Provide sunshades over the window or recess the window to stop the sunlight reaching the wall.
  • Avoid spotlights: Avoid spotlighting or wall mounted up-lighting, or be careful about where these lights are directed and the angle at which they hit a surface particularly near jointing.

Design an effective and efficient lighting scheme

Light has the power to characterise and accent rooms. It can convey an aura of intimacy, provide a touch of sophistication and enhance a home’s architectural details with special effects. Good lighting is about more than just light levels. The same level of light can provide effective or ineffective lighting. Some lighting can make rooms flat and featureless even when it’s bright. An efficient and effective lighting system will:

  • Provide a high level of visual comfort
  • Make use of natural light
  • Provide the best light for the tasks commonly undertaken in that space
  • Provide controls for flexibility (eg. dimmers)
  • Have low energy requirements

A specialist lighting designer can help you design an effective lighting scheme. Ensure you have a detailed lighting plan before construction so that all wiring, cabling and factors influencing the quality of finish can be allowed for. The choice of decorative colour and lighting can have an adverse impact on the flat appearance of interior walls and ceilings.


Lighting and installation methods must be considered at the design stage of the project so the expectation of the interior finish can best be delivered by all parties.

Next month, we will continue discussing the fundamentals of a quality interior finish, with a look at what you can do to reduce imperfections when finishing and decorating plasterboard walls.

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