Pre-painted Galvalume® Sheet:
A Guide to Best Practices
Steel Roofing Care should be exercised on the jobsite to ensure the optimal performance of prepainted GALVALUME sheet. The first step is to become familiar with the simple concepts presented on the next pages.
Transit abrasion usually appears as scuff marks or particles of the backer coat which have been transferred to the top side paint coating of prepainted GALVALUME building panels. This damage can result from improper paint curing, improper handling or shipping practices and metal surface irregularities.
The degree of paint coating cure, or hardness, as well as lubricity, may affect the susceptibility to transit abrasion damage. External rollforming lubricants, internal paint lubricant additives, and properly formulated backer coats can help minimize this damage. In some cases a clear, protective, strippable film (Figure 6) is applied to the topcoat surface to help guard against transit abrasion damage.
In-plant handling of bundled panels can induce abrasion damage. To avoid panel flexing and consequent panel abrasion, long-panel-length bundles should be lifted with equipment that supports most of the panel length.
Bundles should be rigidly packaged with crosswise and lengthwise blocking. Truck loadings should insure that panel bundles are protected from contact with other items such as structural components. When using a forklift, careful handling and unloading practices should also be used to avoid excessive bundle flexing or abrasion of the panels (Figure 4).
Figure 4 - Handling GALVALUME Panels With A Forklift
When lifting bundles with a forklift, forks must be a minimum of five feet apart. Do not transport open bundles. Drive slowly when crossing rough terrain to prevent panel buckling.
Metal filings, drillings, cuttings and other metal debris, such as pop rivet stems and fasteners, should never be left on the prepainted steel surface. As the debris weathers over time it will cause rust stains. These particles should be removed from panels as soon as they are noticed and swept from the roof at least at the end of each day during construction (Figure 5). Avoid walking on them to prevent damaging the paint film. For critical applications, the building should be inspected within two weeks after erection, so that any remaining particles that may have rusted from exposure to dew and rain can be removed. Removing the last vestiges of metal debris at this time will enhance the long-term appearance of the roof.
Figure 5 —
Installation Debris Should Be Swept Away Daily
Figure 6 —
Protective Strippable Film
Some prepainted steel sheets are supplied with a specially-designed clear, strippable organic film. This film protects the painted surface against abrasion during storage and handling and should be removed immediately after installation. Sunlight can increase the adhesion between this film and the painted surface; hence it is vital that the sheets not be left uncovered at the job site (Figure 6).
When possible, cutting of sheets at the job site should be minimized by using factory-supplied cut-to-length sheets. If required, panels can be cut by using straight blade shears, profile shears, nibblers or hand snips.
It is important that all jobsite cutting practices give a clean-cut edge without damaging the paint or metal coating. The shear blades should be kept sharp to minimize burrs. Shearing of prepainted steel sheets should be done with the critical (exposed) surface uppermost so that any small burrs are on the unexposed side.
Never perform field cutting over the top of other painted products. If power cutting or drilling is required, the area around the holes and cuttings should be masked with tape or covered with rags to protect the paint from the hot filings. Cutting with an abrasive disc or hacksaw or burning through with oxyacetylene or similar torches should be avoided to prevent damage to the paint and metal coating.
Accessory Materials Compatibility
Copper, lead, graphite and unprotected steel should not be used in contact with prepainted GALVALUME sheet. Water run-off from copper should be avoided. Prepainted GALVALUME sheet should not be used in direct contact with wet and/or weather-treated wood or uncured concrete. Wood retains moisture, and weather treatments contain corrosive chemicals that can shorten the life of a panel in direct contact. Run-off from chemically-treated wood may also cause corrosion. Uncured concrete is highly alkaline and may attack the aluminum-zinc coating.
Due to galvanic action, lead and copper flashing can cause accelerated corrosion of prepainted GALVALUME sheet. Lead flashing is incompatible with GALVALUME sheet. Copper flashing is incompatible with both galvanized and GALVALUME sheet. For metal flashing, the preferred alternatives are bare and prepainted GALVALUME and aluminum sheet. Due to its shorter service life, galvanized sheet should not be used as a flashing material with prepainted GALVALUME sheet. Graphite-free rubber and aluminum factory-made roof penetration flashings, such as those for vent pipes, should be used with prepainted GALVALUME panels.
Handling and Storage
Failure to observe simple but essential precautions when storing and handling panels on site can lead to damage, delay and expense.
- Panels in bundles should be lifted at their center of gravity.
- When lifting bundles with a crane, a spreader bar and nylon straps should be used. Never use wire rope slings.
- When using a forklift, forks must be spread a minimum of five feet (Figure 4 above).
- Individual panels should be lifted vertically by the seam. Do not pick up panels by the ends.
- If the panel is over 10 feet long, lift it with two or more people on one side to prevent buckling. (Figure 7)
Figure 7 - Lifting GALVALUME Panels By Hand
Standing on one side of the panel, lift it by the seam. If the panel is over 10’ long, lift it with two or more people on one side of the panel to prevent buckling. Do not pick up by the ends.
The following practices should be used to avoid damaging prepainted GALVALUME panels during shipment and installation (Figure 8):
- Panels should be kept dry in transit.
- Panels should be handled and installed using clean, dry gloves.
- Panels should not be pulled over rough surfaces, or over each other.
- Panels should be stored off the ground on skids — at an angle for drainage — and protected with a loose-fitting waterproof cover.
- If bundles become wet, panels should be separated, wiped with a clean cloth without delay and stacked so that air circulation completes the drying process.
Figure 8 - Shipment And Storage Of GALVALUME Panels
- Where possible, do not leave uncovered coils or packs of panels lying in the open. Store indoors and always away from openings to the outside. However, if it is absolutely necessary to store GALVALUME panels outdoors, the n the following simple precautions are essential.
- If packs or coils cannot be kept under cover, erect a simple scaffolding around them and cover with a waterproof tarpaulin or plastic sheet. Leave space between the cover and the sheets to allow air to circulate.
- Store packs off the ground and on a slope so that if rain should penetrate the covering, water will drain away.
- Inspect the storage site regularly to ensure that moisture has not penetrated the pack.
Backfill and Foundations
Avoid backfilling with soil against prepainted GALVALUME siding surfaces. If backfilling is inevitable, the sheet surface needs to be isolated from the backfill by using barrier films.
Ideally, sill plates should be used when installing prepainted sheets over concrete foundations. However, the prepainted siding should not be in contact with the sill plate. Sill plates should be tilted slightly away from the building to avoid trapping water and providing for drainage away from the edge of the prepainted GALVALUME sheet.
Fiberglass blanket insulation with a vinyl vapor barrier is generally used on walls and under roofs on buildings with prepainted GALVALUME roofing and siding. Under circumstances in which insulation contacting prepainted GALVALUME panels gets wet, inside-out corrosion can occur on the panels. Vulnerable areas are at wall panel ends at the bottom sill or footing and at the eave. Insulation should be installed above the sill so that the insulation won’t get wet and act as a wick to cause inside-out corrosion (Figure 9). Likewise, insulation not properly tucked in under the roof and at the top of the wall panels can be exposed to condensation and wind-blown rain, causing underside corrosion of the roof panel.
Figure 9 - Typical Siding And Sill Plate Details
To avoid wet insulation at the footing, several inches of the fiberglass insulation should be removed from the vinyl vapor barrier at the end of the blanket. The vapor barrier should then be folded up and around the insulation, as illustrated, and placed between the panel and the sill plate or base angle, depending on the footing installation arrangement. A sill plate arrangement is recommended because it prevents entrapped water, wet insulation and contact with concrete. In addition, contact between the GALVALUME panel and the sill plate (or concrete) ideally should be avoided.
Installation practices that allow the insulation to become continually wet simply should be avoided. Fiberglass blanket insulation under GALVALUME roofs needs to be installed in such a way that all vapor barrier seams are sealed, and punctures, penetrations or holes in the vapor barrier are repaired. Condensation of water vapor on the underside of the roof, along with saturation of the insulation, can cause inside-out corrosion.
Certain types of field-applied spray-on insulation contain chemical fire retardants that may be corrosive to GALVALUME sheet. Check with insulation manufacturers before using such products.