Maintenance is defined as 'to keep in good condition or repair', and can be divided into four categories:
- Reactive
- Scheduled
- Preventative, and
- Special
COP v24.03:Maintenance;
- Section B2.3.1 of the NZBC requires components to satisfy the requirements of the building code, for 50, 15, or 5 years (according to their categorisation) with only Normal Maintenance.
- B2/AS1 section 1.2.1 defines 'normal maintenance' as: "work that is generally recognised as being necessary to achieve durability for a given building element…."
- B2/AS1 Section 2.1 states that it is the responsibility of the person specifying the building element to determine Normal Maintenance requirements which may be based on the manufacturer's recommendations
- B2/AS1 section 2.1.3 gives examples of Normal Maintenance as:
a. Following the Manufacturer's maintenance requirements.
b. Washing down surfaces, particularly exterior building elements subject to wind-blown salt spray.
c. Recoating exterior and interior protective finishes.
In general, NZ metal roofing materials exposed to rain washing can be expected to comply with NZBC B2 without manual washing, or replacement of protective finishes — but unwashed areas, which includes all wall cladding, may require maintenance.
Where access for maintenance of unwashed areas is impractical, the use of non-ferrous metal cladding may be advantageous in meeting NZBC requirements.
Whether or not regular washing is required by the manufacturer, inspection should be programmed to give early identification of any problem areas. This should occur at all washing intervals or at least annually. Observations from this inspection can be used to determine frequency requirements of general washing, and whether any high-risk areas, for instance around flues or outlets, sheltered areas of roofing, or areas contaminated by birds, require more frequent attention.
Reactive maintenance is the response to a maintenance need that is visually apparent.
The disadvantage of this model is that preventable permanent damage to the cladding may already have occurred. A proactive scheduled maintenance approach is preferable to achieve optimal life cycle costs of the cladding.
Spray cans should not be used for repairing scratches on pre-painted cladding. Minor surface scratches are best left because they become less noticeable as the coating weathers. If the scratch cannot be seen from the ground, it should be left alone.
Scheduled maintenance is routine maintenance that is performed at pre-planned regular intervals. Inspection should always be an included part of scheduled maintenance.
Washing Cladding
The accumulation of deposits on a metal surface may increase the time of wetness of that surface and also increase the corrosivity of the wetness. Most exposed metal roofing will be adequately cleared of dirt by rain washing, but that is not the case with unwashed areas. Unwashed areas include all wall cladding. It is particularly applicable to areas directly sheltered from the rain, which includes all surfaces that are above a line drawn at 45° to an overhang, such as a soffit, underside of a canopy, under spouting, or garage door head.
Manual washing is required to prevent the accumulation of dirt, debris or other material not removed by rain on these surfaces, carried out at intervals as prescribed by the manufacturer.
Generally, metal wall cladding subject to some direct rain should be washed:
- every 6 months in severe environments; and
- every 12 months in moderate environments.
Generally, other unwashed areas should be washed:
- every 3 months for severe environments; and
- every 6 months for moderate environments.
Washing can be carried out with water and a sponge, soft brush or broom, or water blaster up to 20 mPa, directed away from the overlap of the sheets. Detergent will help remove deposits if it can be applied without increasing the risk of slip and fall.
Preventative Maintenance is work that provides extra protection in high-risk and vulnerable areas and is intended to prevent or minimise later requirements for reactive maintenance. It can be achieved by enhancing the product before installation, or by maintaining such areas more regularly than the body of the cladding.
Where the underside of metal roof cladding is subject to contaminants such as salt at the gutter line, an eaves flashing should be inserted under the roof and over the gutter to prevent deposits which lead to 'inside out' corrosion. This flashing can assist where dissimilar metals are used for gutters, or spouting where splashes and contaminants can corrode the roof cladding. (See 8.5.5.4 Eaves Flashing). Where the gutter line micro-environment is likely to be severe, the exposed underside of metal cladding can be painted using a two-pack epoxy primer or elastomeric polyurethane paint before installation.
The most efficient protection of the eaves in severe marine areas is to use a high front spouting system where the front face of the spouting meets or exceeds the height of the roofing crests. These can be custom folded if necessary.
Seagulls perching on ridging, parapets or aerials on buildings can cause damage from rubbish dropped onto the roof, and from their alkali droppings. Discouraging devices such as wire or spikes can be used to prevent this. Unpainted aluminium or AZ coatings are particularly vulnerable to alkali.
Roof Cladding exposed to the elements from the underside should be included in the maintenance schedule for unwashed areas.
Special maintenance is related to preventative maintenance in that is focusses on vulnerable areas.
High-risk areas such as those around flues, near fumes from exhaust fans, under television arials or overhanging trees, or sites prone to mould, lichen, and bird droppings or debris may deteriorate faster than surrounding areas. Proximity to a motorway can cause the collection of contaminants and fine dust, as can nearby earthworks. Shavings from wood processing plants are often blown into crevices under flashings; the shavings retain moisture and can create poultice corrosion. Such areas may require more frequent maintenance than adjacent areas.
Details that trap debris against the roof, such as loose cables or gutter leaf guards, can be removed to allow free draining of these areas. Soil or lush vegetation at the base of wall cladding can also be removed to prolong the life of the cladding material.
Regular washing of pre-painted and metallic-coated roofing products increases their durability by reducing attacks from airborne salts and pollutants.
Washing may be carried out with a hose and a soft bristle brush, using fresh water or a 10% solution of household detergent and water followed by a thorough rinse with clean water. Alternatively, low-pressure water blasting can be used at pressures up to 20 MPa, with the jet directed away from openings and sheet laps.
Stronger concentrations of cleaners than those recommended can damage coating surfaces, and avoid using organic solvents and abrasive cleaners. When cleaning coated surfaces, tar and similar substances may be removed with mineral turpentine, but the surfaces should then be washed thoroughly with detergent and water.
Always clean coated surfaces from top to bottom, and rinse immediately and thoroughly with fresh, clean water avoiding over-cleaning or scrubbing, which can damage painted surfaces.
Hard scrubbing of un-weathered bare AZ-coated steel cladding can remove the thin factory-applied clear acrylic film and cause differential weathering, affecting appearance.
If water runoff is used for drinking water, roof outlets must be disconnected before washing any roof or wall cladding using detergents. Care must also be taken not to contaminate waterways.
Lichen is a naturally occurring phenomenon with its spores being dispersed by the wind. Lichen will grow even on inert materials such as G.R.P., glass, and painted or unpainted metal roofs.
Time of wetness of a surface affects lichen and mould growth. Sheltered and shady environments are particularly conducive to its growth and although light-coloured roofs may stay wet for longer than dark roofs, it can equally proliferate in open areas on dark coloured roofs.
Lichen and mould retain moisture, are acidic, and have tiny roots that can penetrate a paint coating. Removal is necessary to prevent damage to the organic coating, but recolonisation is very likely. Where lichen has been treated, regular inspection should be undertaken to curtail spread of re-growth.
Lichen growth can be removed by washing down the roof or wall cladding, and applying a 2% solution of sodium hypochlorite to all surfaces by low-pressure spray, broom or brush. The surface should be left for 5 minutes but should then be rinsed and thoroughly washed down with cold water. Household bleach contains various concentrations of sodium hypochlorite; therefore, it may be necessary to dilute it.
For example:
- One brand has 30 g/L solution (3%) — to obtain a 2% solution, 2 parts of bleach should be diluted with 1 part of water. (3 - 2 = 1).
- Another brand has 40 grams/L solution (4%) — to obtain a 2% solution, 2 parts of bleach should be diluted with 2 parts of water. (4 - 2 = 2).
- Another brand has 50 grams/L solution (5%) — to obtain a 2% solution, 2 parts of bleach should be diluted with 3 parts of water. (5 - 2 = 3).
Another option is using benzalkonium chloride products which are less corrosive, although slower acting.
Metal wall cladding, like most vertical surfaces, is subject to being defaced by graffiti. Graffiti removal is likely to affect the pre-painted finishes on metal roof and wall cladding, and before removal is attempted a small area should be cleaned as a trial. Graffiti removers may soften the paint, remove the gloss or cause permanent damage.
Do not use MEK (methyl ethyl ketone), toluene, acetone or thinners. Overpainting or replacement are the alternative options.
There are clear anti-graffiti coatings available, but their compatibility with the pre-painted cladding must be checked with their supplier.
As with all surfaces, the overpaint performance on profiled metal surfaces is dependent on correct surface preparation as well as application. This clause provides generic recommendations; in all cases, the advice of the paint supplier should be studied and followed.
- Thoroughly clean the surface with fresh flowing water and a medium stiff nylon bristle broom, or water blast at 20 MPa. When cleaning the profile to remove dirt, lichen, mould, or algae, care should be taken not to drive water under laps or flashings. Detergent or proprietary roof wash may be added (if safe) to aid dirt removal, but if used should be flushed off with fresh water before drying.
- Rinse the profile thoroughly, as any remaining dirt will impair subsequent paint adhesion. Particular attention should be given to the drip edge (where the final 15 mm is prone to heavy dirt build-up), and to the coating at the front edge of tile profiles, as dirt collects in this area leading to mould, algae, and lichen growth.
- Fallout around flues and vents needs to be removed before painting.
- Allow the roof to dry.
Thorough washing will remove most light deposits, and coating loss may be compensated for with metal-rich primer. Heavy deposits may require the same treatment as rust.
Manually abrade the red rust down to bright metal, being careful not to overly remove adjacent metallic coatings. Prime with a metal-rich primer and overcoat with an anti-corrosive primer and compatible topcoat.
The use of rust neutralisers is an alternative but must be used with caution. Many are aggressive to remaining metallic coatings, some retain corrosion salts which may cause undercut corrosion in the future, and some, if not completely removed after application, will accelerate corrosion. If considering this path, use it strictly according to the manufacturer’s recommendations and requirements.
High-quality, 100% acrylic paint can give a service life of up to 10 years or more when applied to specification on correctly prepared metal surfaces. This lifespan will vary with colour, roof orientation and the aesthetic requirements of the situation. Poor paint curing will downgrade durability.
For many paints, a 50µ dry film build is required to achieve optimal thickness, and typically this requires two layers of top-coat.
Paint should not be applied on wet days when condensation has not completely dried, or when ambient temperatures are expected to reach less than 10° or more than 30° within the drying period. Windy days are also not recommended, as curing is impaired.
Ridge ladders should be fitted with protective buffers or rubber pads as they can cause abrasion damage to pre-coated metal cladding. Where it is possible the painter should walk in the pan, but when it is necessary to step on the rib, (only at the purlin line) attention should be paid to sheet overlaps as these may spring up after a painter's weight is removed and reveal an unpainted line.
Decking profiles have a tight roll-formed bend at the top of the upstand and care is necessary to ensure the specified film build is applied in this area.
Brush Application:
The use of nylon brushes is advisable, and these should be wetted with water prior to use to avoid clogging, and in warm weather should be washed out completely at every rest break, or wrapped in cling film and refrigerated.
Roller Application:
Roller application is not preferred for profiled metal roofing as it tends to apply an uneven paint film thickness. The combined use of brush and roller can give good results with tray profiles.
Dampen the roller prior to use, apply with even pressure, and do not over-roll.
Spray Application:
Spray application in the hands of a skilled applicator can achieve the most consistent film builds. However, airless spray equipment can produce very high film builds giving rise to runs and uneven coatings. When using spray equipment on hot or windy days, the paint spray may dry before it has reached the metal, which leaves a sandy appearance and feel. This is not aesthetically acceptable and will not provide the even coating or durability required.
The practice of leaving metal-coated roof cladding to weather before painting is no longer required. With the latest developments in primers, roofs can now be painted immediately after installation.
- For un-weathered AZ-coated cladding, only acrylic galvanised iron primers should be used, as solvent-borne primers may damage the coating. A solvent-borne corrosion-resistant galvanised-iron primer should, however, be used for optimum performance on weathered AZ or galvanised-coated cladding. Wash and allow to dry (see preparation above.
- Apply primer.
- Apply two coats of acrylic roofing paint in the selected colour to provide the required paint thickness. (Typically two brush-applied coats achieve 50 µm).
Repainting painted cladding should be regarded as part of the maintenance programme to extend the life of all metal cladding.
The optimal time to overpaint weathered pre-painted cladding is when the colour has faded excessively, or the topcoat has eroded to the point that the primer is becoming exposed.
The gloss and weathering characteristics of oven-cured and air-dried paints are different, and over time a significant difference in colour may become apparent. Variations in natural light conditions will emphasise these differences producing unacceptable aesthetic variations. For this reason, the whole roof area should be painted and not patch-painted.
- If the over-painting is carried out while the topcoat is still in sound condition, there is no need to use a primer.
- Apply two coats of acrylic roofing paint in the selected colour to provide the paint thickness. (Typically two brush-applied coats achieve 50 µm ).
It is not easy to obtain adhesion to unweathered pre-painted metal cladding. To prepare such surfaces for painting, abrade all surfaces with fine grit sandpaper, stiff nylon bristle broom or similar, to improve the adhesion. Care should be exercised not to sand through the existing paint surface on external bends.
If the purpose of overpainting new cladding is to obtain a colour finish that is not available in pre-painted material, it is often more economical to order pre-primed material rather than try to overpaint an un-weathered pre-painted surface.