Coatings and Finishes - Steel - Blog 14 - Yukta Yogeesh

22/September/2020 


Coatings and Finishes 

 
It takes me back to my initial blogs where I quoted that "God is in the Coating". Seems like that’s not an amateur statement to make. The productivity, especially, in huge spans and in large structures depend legitly on the type of the coating and finishes the members obtain. The efficiency of Steel members is directly proportional to the type/ quality of coating. 


 Although steel was introduced in building construction because it was fire resistant, to replace timber, Steel itself is not that Fire Resistant. Another major disadvantage with steel with respect to context is the weather. Humidity causes Corrosion and rusting is evident. Certain issues pertaining to the Cleanliness and Maintenance also add to this list, like the trusses becoming a roosting place for pigeons, problems regarding the height of the structure and the equipment required to clean it. The frequency and efficiency of maintenance has a big role to play with the lifespan of the structures. All these factors demand the need of a quality coating and finishes for the Steel Members. 

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Criteria to choose the proper Finishes and Coating 


(Image showcasing the different types of Finishes a fabricator can opt for various steel members)

Location 

  • The nature of Exterior and Interior conditions, Weathering, Atmospheric Pollution, Ice, Snow, Rain, Corrosion, etc has to be considered based on the location of the site or the shop preparing the members for the design.
  • For choosing shop work/ on - site, location is essential to calculate transportation distance, cost, etc. 

 

Appearance and Exposure 

  • If the fabricator wants to reveal / exacerbate the connections, they can opt thin / glossy finish.
  • If the fabricator wants to conceal/ potentially hide the joinery, they can opt for matte / mottled / thick finish for their steel members.
  • The fabricator should choose between aesthetics and fireproofing while the latter is better than the first to make it more functional.
  • Style of Exposure - Techtronic and rough or Plastic and extra smooth finish.
 

Adaptations to make steel more effective with better Finishes and Coatings for the members in the Structure / Building Components 

 

  • Closed volume should not be galvanised (hollow). It leads to explosion. A vent pipe can be provided for air access.
  • Paint Systems -Light coloured if you want to reveal / expose the connections.
  • Primer - Each system requires each specification.
  • Tender Document Specifications - Should mention member identification of members, degree of cleanliness, performance, SSPC - Steel Surface Preparation Standards, Manufacturer's Identity, Thickness of the coating, compatible primer, intermediate coating and Finishes.

 

Surface Preparation

Surface Preparation has a major role to play in the productivity of the Steel. The properties they exhibit 

Uniform textured surface can be provided with the help of Sandblasting

It also varies with the surface appearance that the fabricator wants based on the HSS members, the amount of dust that accumulates, the height of the structure and the availability of equipment for the maintenance of the particular members. 

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( Image showcasing impact of Intumescent Coating on steel members.  ) 
 

The different methods of Coating are as follows - 


Intumescent coating 

  • The coating swells to create another layer which is fire protective.
  • Acrylic or Epoxy based coatings are also available in shop fabrication
  • This is not preferred at high traffic locations.
  • It can be used for all types of connections - bolding, welding and casting.

 

Cementitious Finish

  • Carbonate Chemical is being sprayed on the members to obtain a cementitious finish.
  • It is fibrous fire protection layer and it is generally used for AESS 1 and 2 categories.

 

Galvanising / Zinc Coating

The temperature is controlled based on the required quality. It is usually 450 degree Celsius. The steel is dipped in molten Zinc to form a sacrificial layer. It prevents corrosion and is effective and adds to the productivity of the structural steel member. It also prevents sideways creep. It’s simply an outer layer that breaks when there is corrosion and prevents the steel member.

 

Seal Weld Galvanisation

It is done for hollow structures. If it is closed, there are chances for it to explode, so an air vent pipe inclusion is essential.

 

Glulam Timber 

It’s a textured type of finish for the Steel members. Glulam expands to Glued Laminated Timber which gives a feel of timber coating on it.

 

Metalizing

It is an advanced technique for coating. It does not require as much curing time as the other coatings. The life span is about 30 years, based on the quality of application. It is applied by spraying. It is done without a dependence on the temperature aspects unlike the other coatings. It also has an additional Green Building feature - No VOC produced. VOC - Volatile Organic Compound that harms the environment in certain aspects. But, because of all these advantages, it is extremely expensive and not so available.


Powder coating steel

Featured snippet from the web

When applied to steel, powder coating provides a protective barrier that helps prevent corrosion. Chip Resistant. Unlike other treatments that can easily crack, peel, chip, scratch and corrode, powder coated steel frames are more durable and can withstand the environment better.

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( Image showcasing the quantity of steel that a structural component contains that has to be maintained amongst all the other factors)


Simple ways to maintain the Coated Surfaces after application  


  • Avoid Harsh Chemical Cleaners.
  • Proper Cleaning and Maintenance to Extend Effective Service Life.
  • Pressure Cleaning.
  • Use a Mild Soap and Water.
  • A Word About Commercial Cleaning Solutions.
  • Protect the Exposed Surfaces with Wax.
  • Pressure Washing a Fence or Gate.


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No. of words - 800

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Yukta Yogeesh 

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