Zinc Coating Weight Guide for Hot Dipped Galvanized Strip
Coating weight decides both how long a part survives outdoors and how tightly it can be bent. Those two pull in opposite directions, which is the whole problem.
What the Number Means
Coating weight is stated in grams per square metre and covers both surfaces together. We supply from 30 to 350 gram per square metre. Roughly speaking, the higher the figure, the thicker the zinc layer and the longer the sacrificial protection lasts.
Match the Weight to the Exposure
Interior, dry and hidden parts sit at the light end of the range. Parts in humid interiors or sheltered exterior positions move up it. Fully exposed outdoor elements and anything near salt sit at the heavy end. Design life matters as much as environment: a twenty year element needs more than a five year one in the same place.
Heavier Zinc Bends Worse
This is the trade off that catches people out. A thick zinc layer has less tolerance for a tight bend and will craze or flake where a lighter coating would survive. If a part has both a long design life and a tight radius, the answer is usually a more formable DX grade rather than less zinc.
Coating and Grade Are Separate Decisions
The full 30 to 350 gram per square metre range is available against both the DX forming grades and the S structural grades. So a purlin can be specified S550GD for load and separately given whatever coating its exposure requires.
Follow Up Questions
Does a heavier coating always last longer?
Is the figure per side or total?
Materials Covered Here
DX51D to DX56D Hot Dipped Galvanized Steel Strip
Forming grade galvanized strip, zinc 30 to 350 g/m2, 0.15 to 1.0 mm, slit 5 to 1500 mm.
View Specification
S260GD to S550GD Structural Galvanized Steel Strip
Structural galvanized strip, zinc 30 to 350 g/m2, 0.40 to 1.0 mm, slit 5 to 1500 mm.
View SpecificationSectors This Applies To
Apply This to Your Own Part
A guide can only go so far. Send the part and we will tell you which way the decision goes in your specific case.