On Thu, 12 May 2005 07:16:48 +0100, Paul Mc Cann
wrote:

Powder doesn't really differ from ordinary paint with the exception of
the use of an electrostatic charge to assist the particles adhere to the
surface prior to stove enamelling.

That's electrostatic spraying. You're applying what's basically standard
paint, but the static charge improves coverage especially round the
back, on corners and in shadowed areas. For flat sheet it's no better
than a simple spraygun, but it's a good improvement for complex shapes
(such as gates).

Powder coating is "coating with a powder", pretty much by definition. A
slightly sticky _powder_ is sprayed with an electrostatic gun, then it's
heated in a stove enamelling oven and only then does the powder fuse. If
you limit this fusion time, there's enough fusion to make it stick, but
not enough to make the surface glossy. You're thus a bit at risk of
operator skill here - too little fusion gives a guaranteed matt without
shiny patches, but it can also be porous (usually on the bottom edges of
rails)

Dipping is similar to powder coating, but it's done by dipping in a
fluidised bed of powder (a bucket, with air blown through the bottom).
It's reasonable to describe either as "powder coating", unless specified
in more detail.

The problem with powder coating is similar to that of Hammerite - the
coating itself is far stronger than the adhesion to the substrate. If
you annoy it, it loses the bond and you get the coating peeling off
wholesale. Dipping gives a thicker coat, so it's more prone to this.
However sprayed powder coatings can be thin on edges, so they may be
more susceptible to wear and the first delamination starting.

Personally I'd much rather hot-dip galvanise a gate, then let it weather
on its own.

--
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