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Introduction
Prefinished
sheet steel building products, such as wall and roof cladding,
liner sheet, flashing, and associated items, have experienced
an enviable growth record during the past twenty years or so.
Coil coated prefinished sheet steel in a variety of colours and
paint systems has greatly enhanced the appearance of thousands
of industrial, commercial, institutional, recreational, residential
and farm buildings, providing an economical, durable and attractive
alternative to traditional materials. As with all materials, a
little care and maintenance pays off handsomely in terms of longevity
and repair costs. The recommendations which follow have been learned
at first hand and represent the collective industry experience
with thin- film paint systems applied to metallic coated sheet
steel by the coil coating process. In this publication the term
"thin-film paint system" refers to a modified silicone
polyester or a fluorocarbon type having a coating thickness about
25um.
When
the guidelines listed below have been observed, thin-film paint
systems have been used successfully for all types of environments
other than severe industrial atmospheres which require special
consideration. The guidelines are not intended for barrier coatings,
laminates, and new formulations which have different characteristics
than the thin-film paint systems on which these guidelines are
predicated.
Design,
Detail and Colour Considerations
- Architectural
details should permit natural rain- flow cleaning of the cladding.
- On
roofs or other horizontal surfaces, standing water can contribute
to the premature failure of the paint system and substrate. Detailing
should preclude damming or ponding of rain-flow at stacks, ventilators,
air control equipment and other objects.
- Due
to colour tolerances, there may be differences in colour shade
between production runs. Where possible, ensure that each building
elevation is clad with material from the same production lot.
If different production lots must be used on one elevation, as
may occur when making an addition to an existing building, try
to begin the cladding on an elevation change or break in the building
to minimize the effect of possible colour variations.
- A
sufficient roof slope to permit drainage is recommended (e.g.
minimum slope 2/12 pitch).
- Roof
surfaces, defined as those up to 60 degrees from the horizontal,
are subject to more severe exposure conditions than vertical surfaces.
Conditions such as extended exposure to ultraviolet light may
be resisted by using a light colour for the roof. Acid precipitation
and drip edge puddling are other conditions that could affect
the appearances and durability of the paint finish. Drip edge
puddling may be minimized with a steeper roof slope or by modifying
the edge details. If severe acid precipitation is experienced,
a more resistant prefinish system may be required.
- The
building design should seek to minimize the installation of mechanical
equipment on a prefinished roof. Walkways should be provided where
regular traffic is necessary for maintenance.
- In
wall applications, horizontal portions of the cladding and base
flashing should be sloped to prevent moisture from puddling.
- Walls
shadowed by overhangs and all soffit areas have an increased time
of wetness relative to other areas. The increased time of wetness
creates a more aggressive environment for the cladding so affected;
therefore, architectural details should try to minimize these
areas.
- To
decrease the visibility of "oil canning", select an
adequate material thickness, a narrower flute and a lighter colour.
- To
prevent unwanted galvanic corrosion, the architectural details
should not allow the contact of dissimilar metals (e.g. steel
and aluminum or copper) or should provide an adequate means of
separation. The path of rainfall runoff should also be directed
to prevent water runoff across one type of material to another
which can also cause galvanic corrosion.
Site
Storage
- Storage
time should be minimized by installing clading panels as soon
as possible after delivery. Good planning will ensure that panels
are used on a first-in first-out basis.
- If
cladding must be stored for an extended period, the most desirable
storage place is under-roof in a cool, dry, well ventilated area.
- When
storing outdoors is unavoidable, the following is recommended:
(1) use good covers, loosely shrouded over stacks and firmly anchored
to prevent wind blow off, but plastic covers should not be used
for storage
(2) tilt bundles for drainage
(3) ventilate bundles but do not allow entry of wind-driven rain
(4) block bundles off the ground for effective drainage and ventilation
(5) block long panels to prevent sagging
(6) store out of direct sunlight if possible
(7) store away from chemically aggressive substances (e.g. salt,
cement, fertilizer), away from material that could contaminate
the surface (e.g. diesel oil, paint, grease) and away from site
traffic.
- Shipments
of bundled cladding panels should be inspected upon delivery.
- Moisture
can cause wet storage staining of prefinished material and usually
occurs in one of three ways:
(1) condensation from high humidity and/or temperature cycling;
(2) wet shipping conditions; or
(3) wind-driven rain penetration (outdoor storage). The usual
progression is from visible water staining to unsightly white
staining (dark grey to dull black on aluminum-zinc alloy coated
material) to red rust. On material where wet storage staining
has occurred, it should be noted that a nominal amount of white
staining is not detrimental to the functioning of the product
and is usually considered acceptable.
Field
Painting and Touch-Up
- Painting
over a new installation is not recommended. All coil coated paint
films have internal additives that do not allow good adhesion
between field-applied paint and the coil- coated paint layer.
Also, because touch-up paint will not last as long as the original,
keep the touch-up to a minimum. A small artist’s brush or a small
air brush should be used. For additional guidance about painting,
refer to CSSBI Fact Sheet 4: Painting of Prefinished Sheet Steel.
- Replace
a panel rather than attempt to touch-up large areas; a spot 20
mm (3/4") in diameter will become more prominent in time.
For repainting, consult a fabricator member of the CSSBI who will
provide recommendations.
Maintenance
- A
thorough building clean-up after completion of
construction should be conducted to remove all debris, metal filings,
metal fines, etc. from walls and roofs.
- An
occasional cleaning of prefinished material can extend the service
life and help to maintain the appearance of the finish. For protected
areas (i.e. overhangs) an annual spring cleaning is recommended.
Simply washing with plain water using hoses or pressure sprays
is often sufficient. Waxing is an additional method of prolonging
the service life of prefinished material.
- In
areas where heavy dirt deposits dull the surface, a solution of
water and detergent may be used: 100 ml (1/3 cup) of a typical
laundry powder detergent per 4 litres (1 gallon) of water. A soft
bristle brush should be used for scrubbing followed by a clear
water rinse.
- Mildew
may occur in areas subject to high humidity. To remove mildew
along with the dirt, the following is suggested:
(1) 100 ml (1/3 cup) laundry detergent
(2) 200 ml (2/3 cup) trisodium phosphate (TSP)
(3) 1 litre (1 quart) 5% sodium hypochlorite solution (laundry
bleach)
(4) 3 litres (3 quarts) water
Use in a well ventilated area and follow with a clear water rinse.
- Solvent
and abrasive cleaners should be avoided. Caulking compounds, oils,
grease, tars, wax and similar substances can be removed with mineral
spirits applied only to the affected areas. Detergent cleaning
and thorough rinsing should follow the use of solvent.
For
More Information
Additional
information on prefinished sheet steel is available in the CSSBI
Bulletin B16-94, Prefinished Sheet Steel for Building Construction
For more information about prepainted sheet steel products, contact
the CSSBI for a list of the Fabricator Members in your area.
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