Steel Construction Vol 40 No 1 - Architecturally Exposed Steel | Page 24

SAISC TECHNICAL

Photo 4

Photo 5

By just taking a short cut bypassing any one of
the preparation steps, your selected corrosion
control systems could end up fatally flawed.
ABOVE FROM LEFT TO RIGHT: Photos 4 and 5.
BELOW FROM LEFT TO RIGHT: Photos 6 and 7.

2. During the fabrication process
a. Cutting those breather/drain holes
i.

It is preferable to drill these holes, and
3D detailing packages talking directly
to NC controlled drilling machines
will insert holes into their exact
position. See photo 1.

ii. With the advent of oxy-fuel and
plasma plate centres, it is now
possible to cut part holes to an
inordinately high standard. See
photo 2.
iii. Oxy fuel hand cut holes should be
avoided at all costs. They are
usually poorly done and are
unsightly as example photo 3, taken
at the high profile Eden project in
England indicates. These hand cut
holes are perfectly placed at eye level
for all to see, what a shame! Photo 4
shows an inappropriate air pocket
leading to an uncoated area and
photo 5 solidified zinc traps as a
result of inadequate or non-existent
coping holes or snipes.

Photo 6

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Steel Construction Vol. 40 No. 1 2016

b. Removal of sharp edges and corners
i.

We know that neither paint nor
molten zinc will stick to sharp edges.

ii. This process falls under the generic
name of fettling which the Oxford
dictionary defines (amongst other
definitions) as to “make ready, put in
order, to scour”.
iii. The Oxford dictionary defines scour
(amongst many others) as cleanse or
polish by hard rubbing.
iv. In our workshops we commonly use
the term grinding to describe how we
remove the sharp edges and corners.
v. Do not forget to remove sharp edges
or burrs for safety reasons. Photo 6
clearly covers all of these points.
c. Remove substances that will be
harmful to the process that follows:
i.

Paint and wax will prevent molten
zinc from reacting/alloying with the
surface of the steel in those areas.

ii. Removal of oil based paint marks will
have to be removed for hot dip
protection.
iii. Boilermakers’ yellow wax crayons
should never be used on steelwork
intended to be hot dip galvanized,

Photo 7

grinding just spreads the wax over a
greater area.
iv. Hydrocarbons (oils and grease) and
other dirt are usually chemically
removed by dipping in the case of the
hot dip process into caustic and acid
solutions, or by using water based
grease removers for painting systems
(shot or sand blasting will only
spread the hydrocarbons over a
greater area with sometimes
disastrous results with paint not
adhering to these areas).
v. Welding spatter and slag fall under
this subject and are usually removed
mechanically.
d. The glaze like silicon slag layer from
the Mig/Mag welding process also
needs to be mechanically removed
(using a needle scabbler machine)
Photo 7 refers.
e. Prepare the surface to receive the
system.
i.

This will always include remove mill
scale and rust which process can be
done by wire brushing, sand or shot
blasting and/or acid dipping.

ii. Paints that are suitable for corrosion
protection do not stick to smooth