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How to prepare a metal roof for successful coating.
Why Metal Roofs Require Surface Preparation.
Metal roofs always require a degree of preparation before they can be painted.
Thorough surface preparation results in a more successful metal roof coating project.
The roof of a building is the element most exposed to the elements and is also the most often negelected area of a building, simply because roofs are difficult to access.
Over a number of years, the roof surface becomes soiled and can also be affected by fungal growth, with moss, lichen and black-spot mould being common.
The protective layer of a metal roof is provided by a factory-applied finish, most often being Plastisol, a thick, leather-grained or similarly emobossed plasticised coating.
The original finish is designed to last 20+ years, but in reality, the actual life can be reduced by a number of factors such as UV radiation, envirnomental conditions and mechanical damage.
Additionally, metal roofs are often affected by cut edge corrosion, a defect that causes the protective finish to peel back from the steel substrate, leaving it susceptible to rust. This is commonly seen at overlapping roof sheet joints and at the eaves.
Cut edge corrosion occurs because the sheet edges are cut to length, leaving the cut edges without any surface protection.
Metal Roof Surface Preparation Methods
Fungicidal Wash: A fungicidal wash is applied to the metal roof surface and left for 24 hours before being rinsed off. A fungicidal wash is recommended where stubborn black-spot staining and lichen is present. Jet washing is also necessary as a fungicidal wash does not clean the surface.
Jet Wash Cleaning: Usually, metal roofs are cleaned before they are coated. This involves using powerful jet washing equipment with rotating jets of water. This method effectively removes surface soiling and most fungal growth.
Coating Removal: Sometimes, a metal roof is being washed, the riginal protective coating starts to come away from the steel substrate. When this happens, it is very important to remove as much of the coating as possible, making sure that any residue is firmly adhered to the surface. This is a time-consuming process that will increase your cleaning costs.Failure to remove loose coatings will adversely affect any new coating.
Blasting: Sometimes, jet washing isn’t enough. If the existing coating is coming away, it can be more cost-effective to use a blasting system to take the surface back to bare metal and completely remove the existing finish.
Cut Edge Corrosion: Where cut edge corrosion or spot corrosion is present, the affected areas need to be abraded back to bare metal, to ST3 standard, meaning a non-polished bare metal appearance. Rust can appear within hours, so abraded surfaces need to be treated with a corrosion primer as soon as possible.
Repairs: In addition to the surface preparation, any additional repairs should also be carried out, so all roof lights, fixings, details and protrusions must be inspected and brought into repair prior to roof coating works commencing.
Conclusion
The most effective way of ensuring a metal roof coating project is successful, is to involve the roof coating manufacturer as early as possible in the process.
Liquasil’s team is made up from our team of building surveyors and we are happy to attend site with professional specifiers, to determine the condition of the metal roof and make any site-specific recommendations to be included in your roof coating specification.
Correct cleaning and surface preparation will result in a more aesthetically pleasing metal roof coating installation and will extend the life of the coating system.
Liquasil Approved Installers will be happy to provide you with more information.
For more information regarding durface preparation for your metal roof coating, please call one of our friendly & knowledegable building surveyors on 0121 709 5352
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