GALVANISING
What is hot dipped galvanised?
This is surely the most cost-effective method and, when utilised in the right environment, can be aesthetically pleasing. Steel is lowered into a ‘bath’ of molten zinc, removed and left to cool.
What other types of galvanising methods are there?
It’s important to distinguish the difference between the processes that may be referred to as ‘galvanised’. The finish normally associated with fixings is BZP (bright zinc plated) which is a thin layer of zinc applied using electrical currents. It is very neat but does not hold up with surface protection with the hot dipped galvanised method and isn’t suitable for larger items. Another method less commonly used is ‘cold galvanised’. This is purely the application of a zinc rich paint. It’s a cheap method and should not be the only protections; see below where using it with a powder coated top coat is recommended.
Is it worth hot dipped galvanising with a powder coated top coat?
To me, it is an unnecessary expense. Very often the 2 processes are carried out by different companies at 2 different locations. Even if that is not the case the steel requires fettling (taking off the sharp pieces of zinc) which can be time consuming to achieve a high finish. The answer here, in most cases, is to use a powder coated zinc primer. Click here to find out more.
Is a zinc rich primer as good as galvanising?
For longevity, the simple answer is no. However it is much cheaper when apply a top coat later as the primer doesn't require fettling or degassing, is less likely to have a reaction with the top coat (we've seen bad cases of bubbling before) and both coats will be done at the same premises.
What is fettling?
Fettling is required to remove the sharp zinc pieces created in the hot dipped galvanising process. This is generally done using soft sanding pads attached to power drills or angle grinders and, for the more delicate jobs, hand files and sandpaper can be used.
POWDER COATING
What is powder coating?
Powder coating is the use of a dry ground polymer resin that is electrostatically sprayed on to a material that is then ‘baked’ or cured in a large oven.
How long does it last and is it worth the cost?
When compared to buying a brush, a tin of Hammerite and wasting a free Saturday, maybe not. Where it really comes into its own is the lack of maintenance. In our experience, after several years the only damage is colour fade; you can view a prime example by taking a look at this bridge we did (5 years between install and photograph).
Is it worth hot dipped galvanising with a powder coated top coat?
To me, it is an unnecessary expense. Very often the 2 processes are carried out by different companies at 2 different locations. Even if that is not the case the steel requires fettling (taking off the sharp pieces of zinc) which can be time consuming to achieve a high finish. The answer here, in most cases, is to use a powder coated zinc primer. Click here to learn more about hot dipped galvanising.
Is a zinc rich primer as good as galvanising?
For longevity, the simple answer is no. However it is much cheaper when apply a top coat later as the primer doesn't require fettling or degassing, is less likely to have a reaction with the top coat (we've seen bad cases of bubbling before) and both coats will be done at the same premises.
What is fettling?
Fettling is required to remove the sharp zinc pieces created in the hot dipped galvanising process. This is generally done using soft sanding pads attached to power drills or angle grinders and, for the more delicate jobs, hand files and sandpaper can be used.
WEATHERING STEEL
What is Corten?
Corten is actually COR-TEN but the latter is rarely used. Originally a trademark, nowadays the term is generally used to describe any weathering steel.
How does weathering steel work?
It's corrosion resistance is unique in that the initial thin layer of rust is what protects the steel underneath. The steel can survive harsh climates and conditions without any need for additional protection.
How long does weathering steel last?
Like all metals, its longevity will be based upon its environment but make no mistake, it lasts decades not years. The Angel of The North was started in 1994 and has only looked better with age and the John Deere HQ in the U.S was clad with weathering steel in 1964. It’s also important to remember how the colour of the steel alters with time.
Why is it so expensive?
Corten is different to mild steel because of the additional metals it contains, namely copper, chromium, manganese, and nickel. This, and the fact that it is manufactured in much smaller quantities and by fewer companies, keeps the price high.
