31 Wemmer Jubilee Road, Village Main
Johannesburg
The Roofing Screw & Fastener Specialist

Which Class Screw For Which Corrosion Environment?

Fastener recommendations for ISO 9223 environments
Our Zap range of roofing fasteners is available in three different coatings for carbon steel fasteners and in stainless steel.
The table below shows the four corrosion resistance classes as specified in SANS1273.

 

CorrosionClasses

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Class 1 is for internal use only and is not applicable to roofing applications.

 

Class 2 (Z2) is for use in urban and rural environments away from industrial pollution and marine environments. The corrosion rate for ISO Class2 environments is 0.1 – 0.7 micron zinc per year.

Our Zap class 2 fasteners are electroplated to SANS1273 specifications with a minimum of 12 micron zinc and can be identified by a Z2 head marking. Recommended for use with Z200 and Z275 galvanized roof sheeting

 

Class 3 (Z3) is for use in mild to moderate industrial and marine environments. The corrosion rate for ISO Class 3 environments is 0.7 – 2.1 micron zinc per year. This environment is described as:

  • Marine environments ranging from 400m to 1000m from breaking surf although prevailing winds and topography may extend this distance.
  • Light industrial environments and environments adjacent to severe industrial environments.

Our Zap Class 3 coated fasteners are mechanically coated according to SANS 1273 Class 3 specifications and can be identified by a Z3 head marking. Recommended for use with AZ150 sheeting; painted Z200 sheeting and painted AZ150 sheeting.

 

Class 4 (Z4) is for use in severe industrial and marine environments. The corrosion rate for ISO Class 4 environments is 2.1 – 4.2 micron zinc per year. The environment is described as:

  • Marine environments ranging from 100m to 400m from breaking surf although prevailing winds and topography may extend this distance.
  • Industrial environments characterised by fall-out and emissions from stacks, sulphur and acid smells. Includes buildings with high internal humidity and / or corrosion from operations within.

Our Zap Class 4 coated fasteners are mechanically coated according to SANS 1273 Class 4 specifications and can be identified by a Z4 head marking. Recommended for use with painted Z275 sheeting and painted AZ200 sheeting.

 

Class 5 is not specified in SANS 1273 but is described in ISO 9223 as very severe industrial and marine environments with a corrosion rate of 4.2 – 4.8 micron zinc per year.

  • This environment includes off-shore areas and up to 100m from the high waterline of areas with breaking surf. Prevailing winds and topography may extend this distance.
  • Industrial environments characterised by heavy fall-out and emissions from stacks, and strong sulphur and acid smells. Very high corrosion rates are evident in most building structures.

Our Zap Class 5 fasteners are made out of 304 stainless steel and can be identified by a Z5 head marking. The Zap Z5 self drilling screws for fixing into steel purlins have a carbon steel section that comprises the drill point and the first leading threads. Recommended for use with aluminium and stainless steel sheeting.

TO SEE THE CORROSION MAP OF SOUTH AFRICA, click here