Often the impact of light (natural or artificial) on a final surface finish of a building element can have a dramatic effect. On occasions property owners will form the view that the quality of the final finish is unacceptable and a construction defect exists. Sometimes further investigation is warranted.
1 Glancing Light – Impacts
Let’s view the above picture taken in different light conditions. Notice the finish to the walls appear different between the two pictures?
As can be seen the different light conditions appear to present the condition of the wall in two very diffident states.
The following examples show a more dramatic position:
It is generally accepted that the effect of the above is caused by glancing light off the surface
2 Glancing Light – How Does it Work?
Glancing light is the light which shines obliquely across the surface of a wall or ceiling. When the light shines at a particular angle it will illuminate one side of the undulation and create a shadow on the other side. Even the smallest imperfections will be visible under some lighting circumstances.
Bob Brown in his Book (Landlinks Press 2009) provides the following diagram to show the impact of glancing light.
So the bottom line is that glancing light can impact how a finished surface can look. The finished surface may look defective when viewed in a particular light but, in a different light the same surface can look significantly different.
Let’s look at another example from Bob Brown’s book:
Same ceiling, dramatically different lighting conditions show the area in vastly different conditions.
And yet another example from Bob Brown’s book:
So as can be seen by the above glancing light can impact the visual appearance of a final surface. As a result when critically assessing the quality of a final finish of a surface it is important that the effects of glancing light are negated. Dulux (“Paints”) in their technical Advice Guide “Preparation – Glancing Light Version 2.02 of 3 notes:
3 Additional Impacts
The quality of the final finish of a surface will also be significantly impacted by the level of finish specified for the surface. While all painted surfaces will require an undercoat and two coats of paint, there can be different levels of finish for the underlying surface. For example, in relation to gyprock walls and ceilings the AS/NZS 2589:2007 Gypsum linings in residential and Light Commercial Construction- Application and Finishing. Part 1: Gypsum Plasterboard specifies 6 different levels of finish. A level 4 finish is the accepted level of finish in domestic construction.
The bottom line when assessing the quality of the final finish of a surface it may also be necessary to consider the specified standard of the finished surface below the painted surface.
4 In Summary
It is important to know about and understand the impacts of glancing light on finished surfaces. As demonstrated the impacts can be significant and can show a finished surface to be substandard, even if it is not.
When assessing the quality of a finished surface it is important that the impact of glancing light are taken into consideration. Placing an artificial light like a torch against the surface to highlight the imperfections is not generally considered an acceptable assessment. There are recommended minimum distances and light conditions during which an assessment of a surface should be assessed.
Houspect prepares independent building inspections reports for clients involved in WA Building Commission and State Administrative Tribunal matters involving the assessment of finished surfaces in new constructions.
5 Need More Information?
28 August 2018
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