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