The Effect of Dirt test
The resistance to weathering also includes an extra test – the ‘Effect of Dirt’ test.
The effect of dirt is a test which comes under the Resistance to Weathering test.
How are plates tested?
Step 1: Dirty the plates
Plates are made dirty so that the background is obscured and left to dry.
The dirt must be:
- a specified viscosity
- no older than 14 days old
- composed of a solution of silica, carbon dust, sodium carboxymethylcellulose and distilled water.
Step 2: Leave to dry
Plates are left for 3 days.
Step 3: Clean the surface
The plate surface is cleaned using a clean mixture of water and neutral detergent (plus a brush if required).
Step 4: take readings on how the plate has responded
Run luminance and retroreflective tests as usual.
What makes a fail:
- Loss of retroreflectivity over a specific tolerance
- Loss of luminance
- Excessive luminance