Corus has more than 40 years experience in the development and manufacture of pre-finished steel for use within roof and wall cladding systems. This supports the provision of best practice advice for the inspection and maintenance of metal envelopes. Good inspection and maintenance practice will repay the careful building owner with the best possible performance in terms of appearance, durability and lifespan.
How often should inspections take place?
Natural breakdown of the coating
Inspection and maintenance checklist
They should be carried out periodically through the building’s lifetime. It is difficult to quantify how often as different building locations and designs will demand different levels of maintenance. It is suggested that the building be inspected after the first year of occupation to assess future maintenance requirements and the duration required between inspections.
In line with Health & Safety Executive (HSE) latest Working at Height Regulations, every effort must be made to avoid having to go on to the roof to facilitate inspections. It may be possible to inspect the roof from a cherry picker, an access hatch or with binoculars from ground level or adjacent buildings.
Colorcoat HPS200® Ultra with its enhanced coating and optimised Galvalloy® substrate, is now maintenancefree for the whole of its Confidex® guarantee period. This means that it will not require any annual inspections for up to 40 years. This supports HSE guidance about minimising roof visits and reduces building service costs.
A build-up of dirt and debris can occur on all surfaces, on all elevations and on roof cladding. Such build-up will be particularly profound at any irregularity, such as at corners, penetrations and gutters. In some environments such as industrial estates and areas close to busy roads, dirt will build up more quickly than elsewhere. Rainfall will have a degree of washing effect. However, any area of the building sheltered from rain, for example the top of roller doors or overhanging eaves, will not benefit from this natural cleaning effect.
Cleaning should be carried out when dirt and debris are visibly apparent, not merely out of habit. The presence of dirt and debris not only affects the appearance, but may also lead to a breakdown of the coating. Furthermore, over many years, corrosion of the metal substrate may occur if a ‘poultice’ of debris, dirt, retained water and aggressive chemicals is allowed to build-up.
Large quantities of debris can also lead to the overflowing or ponding of water, particularly in guttering, which may also lead to corrosion. To avoid this, debris should be swept into a pile, using a stiff, soft-bristled brush and removed. Shovels or hard tools should be avoided. All dirty areas should then be washed down using clean water. Do not use salt water or high pressure jets with a hose. If necessary use a recommended cleaning product, or a 10% solution of a good household or industrial detergent, before applying a final hose down with clean water. A soft-bristled brush can be used for particularly stubborn deposits.
Oil can be removed by wiping the area with white spirit before cleaning and rinsing as for general dirt and debris.
In some areas birds can be a nuisance. A build-up of bird droppings can occur on roofs and this may significantly alter the pH of the surface water run-off. Buildings used as communal roosts, where an excessive build-up of bird droppings is possible, should be regularly monitored and cleaned down.
Graffiti can be removed with specialist cleaners, and over-paint systems are available. These fall into three categories:
- Specialist graffiti removal products such as solvents and gels.
- Waxy sacrificial anti-graffiti treatments can be applied to the pre-finished steel. These can be power-washed off, removing graffiti and the treatment at the same time. Re-application of the treatment would then be required.
- Permanent coatings can also be applied. These render any graffiti easy to clean off, using hot water or cleaning solutions and do not need re-application after the graffiti is removed.
Fungal growth can occur on virtually any surface when the micro-environment is conducive to it. Colorcoat HPS200® Ultra and Colorcoat Prisma® are formulated to be resistant to mould growth but in extreme circumstances this can still be problematic. In general, fungi grow as a result of certain conditions, such as the presence of fungal spores, moisture and also of nutrients from various types of dirt. As with dirt and debris, fungal growth will not only affect the appearance, but can also lead to a breakdown of the coating and ultimately result in corrosion of the sheet. Washing the surface can remove fungal growth. A basic solution may be applied to a pre-washed surface by means of a low pressure spray or brush containing:
- Household detergent - 0.5%
- Trisodium Phosphate - 3.0%
- 5% Sodium Hypochlorite solution - 25.0%
- Clean, fresh water - 71.5%
This should be rinsed thoroughly with clean water after treatment.
Physical damage may occur for a number of reasons such as impact and abrasion. If there is minor damage, such as scuffing of the paint coating less than the depth of any emboss, then no remedial action is required. If there is more serious damage, such as breaching of the paint coating, then remedial action is suggested. If the coating has been breached, then the metal substrate will be vulnerable to corrosion. The repair of breaching should be carried out by removing any loose or flaking paint, cleaning the area and, when dry, covering the breach using a recommended touchup paint. If the zinc coating has been breached, exposing the underlying steel, then application of an air-curing zinc rich paint can be used to replenish the sacrificial protection layer. It is important to ensure that any applied paint is no wider than the original scratch.To achieve this, the paint should be applied with a medium-to-fine artist’s paintbrush. If the damage is extensive, the panel should be replaced, which is easy to do with pre-finished steel.
In the case of natural breakdown of the coating, a decision must be made as to the severity of the breakdown. Ultimately, over-painting or re-cladding may be necessary. The minimum Period to Re-paint Decision (PRD) is the minimum length of time before any such decision will be necessary for a given prefinished steel product. Caution must be exercised as over-painting is not simply a case of applying proprietary paint to the surface of the cladding. It is important that a compatible coating solution is defined and the use of an approved contractor will ensure correct application. Corus can recommend appropriate over-paint solutions.
Metallic debris, such as swarf, rivet stems or other debris that may remain after construction or modification to the building will be vulnerable to corrosion, leading to an unsightly staining of the cladding. Debris of this nature should simply be removed at as early a stage as possible carefully so as not to damage the underlying coating.
Staining caused by the corrosion of construction debris can be removed using a 5% Hydrochloric acid solution. This should be followed by thorough washing and rinsing as with general dirt and debris. Specialist cleaning products may be required for particularly stubborn marks.
Other debris may include expanded foam, bitumen, tar and mastics, all of which require specialist cleaners. Concrete, cement and plaster may also be present as debris and can be removed with a 5% phosphoric acid solution. This should be followed by thorough washing and rinsing as with general dirt and debris.
If strippable film is left in place for too long then, under the action of Ultraviolet radiation from sunlight, the adhesive sets and the tack increases to the point where the removal of the film becomes difficult and sometimes impossible. This can also apply to UVopaque black films if left for long enough. The removal of bonded film or residual adhesive can typically be carried out using WD40 or white spirit, followed by thorough washing and rinsing as with regular dirt and debris. It is important that manufacturers’ specific advice on film removal is always followed.
Fasteners which are faulty through damage or corrosion should be removed and replaced. Corrosion can lead to unsightly staining and potential corrosion of the cladding. Caps, if used, should be placed over uncovered fasteners, or replaced if damaged. Inappropriate fasteners of incorrect material or design should also be replaced as again they could lead to corrosion of the panels.
A cut edge is an area of exposed substrate where a pre-finished steel cladding panel has been cut. All exposed, site-cut edges must be produced to an optimum standard. Where it is not possible to protect the site cut edge from weathering by a cover flashing, they should be treated with a suitable edge protection paint or lacquer. The requirement for this sort of protection is particularly important in:
- Highly aggressive environments such as marine and industrial.
- Low and very low-pitched roofs.
Burrs at cut edges should be minimised by effective shearing practice. Where possible the down burr edges should be on the down slope edge of the roof pitch. On damaged edges, remedial treatment is achieved by abrading back the effects of corrosion and then applying a suitable primer and topcoat to match the colour of the existing cladding.
Check around existing penetrations, such as pipe-work and rooflights where the panels have been breached. Clearly, these penetrations have a significant cut edge and so should be treated as for site cut edges, or sealed using recommended solutions. These areas will be vulnerable to corrosion and ponding, which should be avoided by using the appropriate weather protection.
| Check for | Action |
| Build-up of dirt and debris | Remove debris and wash these areas. |
| Build-up of fungal growth | Remove growth and wash these areas. |
| Physical damage and natural coating breakdown | Assess the extent of the damage or breakdown and either repair it with touch-up paint, replace the panel or over-paint using a specialist contractor. |
| Construction debris | Immediately remove all debris. |
| Strippable film | Remove the film and wash these areas with an appropriate solution. |
| Faulty fasteners | Replace the fasteners and any missing caps. |
| Site cut edges | Use approved maintenance products. |
| Penetrations | Use specialist contractors and approved maintenance products. |
