Chalking Rate Tester according to Kempf Model 241

Description

The first sign of a paint coating being affected by the weather is an initial disintegration of the surface film where some of the pigment becomes loose when originally firmly held in the paint by means of a bonding agent. This stage of deterioration can be shown by simply wiping the surface, loose pigment particles will be removed. This is called „chalking“.

The sooner the paint commences to chalk, the sooner the decomposition of the film has begun; the life expectancy of the finish will therefore be accordingly shorter.

Self-cleansing paints

On the other hand, paints are being manufactured nowadays which are accurately adjusted for a predetermined chalking effect. Such self-cleansing paints renew their surface after every rainfall by the washing off of the contaminated pigment. Their life is practically the same and they show a high degree of colour durability and cleanliness.

Purpose and application

The quantitative determination of the chalking rate is therefore of great importance for

• The choice of the correct raw material for each intended purpose
• The determination of the maximum pigment/volume concentration in respect to weathering resistance or self-cleansing properties
• The evaluation of natural or short-term weathering tests
• A comparative assessment of raw materials and finished products (testing of competitors' samples)
• Determining the maximum warrantable period for large contracts
  
  

Principle

The pigment particles, lying loose on the film surface because of binder decay, are pressed under a specified pressure (250 N) into the steeped gelatine of photographic paper. In accordance with the relevant evaluation method, the impression in the photographic paper is visually compared with a chalking scale or a comparison paint.

Design and operation

The Kempf Chalking Tester, Model 241, consists of a light metal cylinder equipped with a 40 mm dia. rubber stamp (Shore-hardness A 60 ± 5). A strong integral spring allows the loading of the punch with a force of between 50 to 250 N. Ring markings engraved at 50 N intervals into the stamp shaft permit the application of lower pressures than the standard load of 250 N.

Guiding the loading device by hand is often not accurate enough for guaranteeing an even pressure over the whole area of the stamp. It is therefore recommended that the special stand (available as an accessory) be used which provides an accurate vertical guide during application of pressure.

Scope of delivery

• Chalking Rate Tester according to Kempf Model 241
• Chalking Scale