Surface protection systems
The starting point: the corrosion environment
Section titled “The starting point: the corrosion environment”The standards classify environments into corrosivity categories, from dry interiors to industrial and coastal environments. That classification says how aggressive the exposure is.
The second input is the design life: how long the protection has to last without maintenance.
The system required follows from the two.
The typical solutions
Section titled “The typical solutions”Hot-dip galvanising
Section titled “Hot-dip galvanising”A dip coating giving durable, maintenance-free protection. Hot-dip galvanising.
A paint system
Section titled “A paint system”Not one coat: primer, intermediate and topcoat together form a system, at a specified film thickness.
The primer provides adhesion and corrosion protection, the intermediate the film thickness, the topcoat the weather and UV resistance and the appearance.
A duplex system
Section titled “A duplex system”Galvanising and paint together. It gives the longest life, because the two protections complement each other.
What decides whether the system works
Section titled “What decides whether the system works”Surface preparation
Section titled “Surface preparation”The most important step and the most often underestimated. The best paint will not hold on poor preparation.
Film thickness
Section titled “Film thickness”Measurable and checkable — the documentation has to contain it.
Connections and edges
Section titled “Connections and edges”Edges, corners and the area around welds are the weak points: the film is thinner there.
Damage during erection
Section titled “Damage during erection”Scratches arising during site erection have to be repaired.
The designer’s task
Section titled “The designer’s task”The drawings have to give:
- the corrosivity category and the intended durability,
- the system and the film thickness,
- the grade of surface preparation,
- the method of repair.
Without these the contractor will choose the cheapest option, and it may not be enough.
The thin-walled side
Section titled “The thin-walled side”For cold-formed profiles the protection is on the coil: the type and quantity of coating can be read from the standard designation. Protection there comes from choosing the right coating class, not from painting. Zinc coating.
The point
Section titled “The point”Corrosion protection is a system, not a product. It starts from the environment and stands or falls on the surface preparation.