Hot dip galvanising is an industrial process whereby the steel fabrications are prepared and dipped into large tanks of molten zinc. 
The molten zinc bonds to the steel forming a thick and durable protection against corrosion/rust.

Galvanising is recommended for most exterior projects, particularly those near the ocean. 

To avoid explosions during this process it is important our fabrications be prepared with venting holes for all hollow sections to allow any gasses to escape during the rapid temperature fluctuations experienced during the dip. 
These same venting holes allow molten zinc to penetrate to the interior of the job providing rust protection on the inside.

It can be painted and powdercoated however it is to be noted that the surface is affected by the zinc with a rough & lumpy finish. 

In some conditions the painted finish can suffer from a white patchy/powdery discolouration over time (similar to salts seeping through a painted brick wall). It may take over a year for this to appear. In most cases it is easily fixed with a minor touch up paint.