FAQs

Condensation forms under/on roof sheeting when the sheeting becomes colder than the air in contact with it. Water vapour carried in the air then condenses on the colder surface of the roof sheet. To minimise the risk of water damage to ceilings or corrosion related to condensation under steel roof sheeting, a vapour barrier should be provided under the sheeting to prevent contact between the moist air in the building and the roof sheeting.

Reflective foil laminates (sarking) which are commonly used to provide heat insulation under roof sheeting can serve a dual function as a vapour barrier, by thoroughly sealing the foil overlaps with moisture impervious adhesive tape.

The laps should be about 100 mm and kept in close contact when positioning the laminate so the tape can be readily applied.

The laminate must be allowed to drape between the roof supports so that the cold temperature of the roof sheeting will not be transmitted to the laminate by contact. If this were to happen condensation could form on the underside of the laminate and may drip into the ceiling space.

Ventilation of the ceiling cavity may assist in the reduction of condensation however it has been shown that ventilation will not completely eliminate the condensation cycle. In certain marine situations ventilation may also carry salts into the roof cavity which will, in the presence of condensation, lead to accelerated corrosion attack.

For more information, please Download Corrosion Technical Bulletin CTB 11 - Condensation and Insulation.

View our page How To Insulate Steel Roofs.

Please view our page Choose fasteners for cladding.

Yes. But before you do, clean the surface. This can be done using a mop or soft bristle brush with non-ionic detergent (such as kitchen detergent) and water. The surface should then be hosed down thoroughly with water and allowed to dry.

If the surface is new, it may contain some residual lubricants from the roll forming process. These should also be removed using the procedure outlined above. If possible, new surfaces can be sanded lightly to enhance paint adhesion. This is not required on older, weathered COLORBOND® steel.

Once the surface is clean, you can directly overpaint it using two coats (preferably) of a good quality water-based exterior acrylic. Please follow the manufacturer's instructions. If the steel is being used to catch drinking water, also check with the manufacturer that the paint is suitable for this purpose.

It's important to note that overpainting COLORBOND® steel will void any warranties issued by BlueScope Steel. Should, for any reason, overpainting be undertaken on behalf of and under instruction from BlueScope Steel, then a future warranty (if any) position will be negotiated between the customer and BlueScope Steel.

This information is intended as a guide only. For more information, Download Technical Bulletin TB 2 - Overpainting and Restoration of Exterior BlueScope Coated Steel Products.

The use of uncoated steel supports for ZINCALUME® steel or COLORBOND® steel is discouraged as the possibility of corrosion of the overlying sheeting may be greatly enhanced. Where heavy steel sections such as hot rolled steel angles are necessary for structural requirements, the steel sections must be post painted with an appropriate high build industrial coating system or galvanised.

Such procedures are regarded as imperative to prevent the deterioration of the steel member and consequently, the rapid degradation of the sheeting. Advice should be sought from reputable coating manufacturers in regard to the specification of an appropriate coating system which will offer suitable corrosion resistance for the particular exposure environment.

For more information, please Download Corrosion Technical Bulletin CTB 9 - Contact With Unprotected Steel Supports.

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Green timber or timber treated with copper chromium arsenic (CCA) should not come into direct contact with galvanized steel, ZINCALUME® steel or COLORBOND® steel because acidic substances from these timbers have a corrosive effect on the metallic coating. The time of wetness of the metal surface is a factor in the overall corrosion mechanism (the longer the product is wet, the greater the corrosion).

Even run off from CCA treated timber can contain corrosive leachate which will cause corrosion if it contacts galvanized steel, ZINCALUME® steel or COLORBOND® steel.

BlueScope Steel recommend against the use of CCA treated timbers for high moisture situations such as roof and ceiling batons, composite fence constructions and built up flooring or external decking which may utilise a metallic coated steel structural support system.

If CCA treated timbers must be used, the timber and/or steelwork must be sealed by fully painting the material prior to installation.

The use of kiln dried or appropriate dried timber species is recommended for any situation where intimate contact between the metallic coated steel and timber is considered.

For more information, please Download Corrosion Technical Bulletin CTB 13 - Contact With Timber

When sheets need to be cut on site the most suitable technique is with nibblers or power saws with metal cutting blades (tin snips can be used although they are difficult to use on profiled sheeting). The use of cutting discs and grinding wheels is not recommended as they generate very hot particles which can damage the coating.

BlueScope Steel recommends the use of cold cutting saw with appropriate blades

• Don't forget to clean up each day. Offcuts and other metal scraps, such as pop rivet stems and fasteners, if left on COLORBOND® steel, may cause rust stains which detract from the finished appearance. Swarf (steel debris produced by drilling and cutting etc) should be swept or hosed from the job each day.
• Care should be taken if hosing off a roof into gutters already installed. The swarf should not be left to sit in the gutters. Maximum care should be taken when attempting to detach swarf which has become stuck. This can be done, but no action which is likely to remove the paint or metal coatings should be attempted. For critical applications, inspection of the job should be made after two weeks when rain or condensation will have caused any remaining swarf to rust, and will highlight affected areas for a more thorough cleanup.
• Sheets should not be dragged across others as scratching will result. Spray packs should not be used to repair any scratches. The paint fades differently. Small scratches are best left alone. If the damage is severe it is best to replace the panel.
• Never use black lead pencils for marking galvanised, ZINCALUME® steel or COLORBOND® steel. Black lead pencils are made from graphite which will react with the coating on these products resulting in corrosion of the coating. The answer is to use any colour pencil but black and clean off any markings as soon as possible.
• This information is intended as a guide only. For detailed assistance with your particular application, please contact us.

When brickwork is completed it is usual to clean excess mortar from the brick surface with an acid solution. If this acid contacts prepainted steel sheeting and gutters, early failure of the paint and corrosion of the metal can occur. The acid can pass through the paint coating at tension bends and attack the metallic coating below.

Acid leaching of pigment directly from paint coatings subjected to acid splash will result in unsightly "bleached" stained areas which will further deteriorate and lead to corrosion.

Acid cleaning of brickwork associated with two storey construction may often pick up lead from lead flashings and re-deposit with sand from the mortar, within the roof gutters. Corrosion of the guttering rapidly follows.

BlueScope Steel recommends that wherever possible acid cleaning should not be conducted after the installation of metallic coated and prepainted steel building components (eg roofing & guttering). However, when this is not possible it is recommended that the areas be appropriately masked during the acid cleaning operation. Where the possibility of splashing the steel component with acid appears to be present, the item should be thoroughly wetted prior to the application of the acid to the adjacent brickwork and then thoroughly washed a number of times, working from the top of the brickwork to allow complete removal of the spent acid products.

For further information, please Download Corrosion Technical Bulletin CTB 15 - Acid Cleaning Brickwork.

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