What to know about repainting a corrugated COLORSTEEL® roof

Summer is time for a roof revival! The roof is your home’s crowning glory, and having it look spick and span infinitely increases street appeal and the overall look of your property. While it is certainly one of the more major home painting jobs, it can be undertaken by most enthusiastic DIYers armed with the right Resene products. 

Not all roofs are the same, so the guide below is focused on everything you need to repaint a COLORSTEEL® pre-coated roof. Preparation is hugely important here, so for the best results possible, do not skip any of the pre-painting steps. 

Depending on the roof’s age and location, there may be corrosion present – white and red rust and areas of flaking paint, with the possibility of mould and/or lichen infestation. Wind-blown salt deposits must be thoroughly washed off with copious amounts of water and the surfaces allowed to dry before painting commences. This work may need to be repeated daily depending on local wind conditions. Wind-blown salt and zinc corrosion products are hygroscopic (they absorb moisture from the air) and will draw water through the coating by osmotic effect. Along with wind-blown salts, all zinc corrosion products must be thoroughly removed before painting.

Note: The process for painting a COLORSTEEL® roof is similar to other painted roofing.

Treat moss and mould with Resene Moss & Mould Killer, using as directed on the label. Keep in mind that for heavy infestations, an additional application(s) might be needed here. 

For lichen infestations, carefully apply with a 1:1 mix of Resene Moss & Mould Killer and water onto the lichen. Leave it for 24 hours before scraping it off or mechanically removing. Alternatively, water blasting is effective at removing lichen (once killed) as well as other contaminants.

Clean up

For roofs coated in a standard acrylic system, use Resene Paint Prep and Housewash, and thoroughly scrub using a stiff nylon brush or broom. Rinse clean. Resene Paint Prep and Housewash will remove surface chalkiness, essentially degrading old paint more effectively than water blasting.

Due to the make up of many precoated metal roofs, a more powerful cleaner may be needed – use Resene Heavy Duty Paint Prep and Oil Remover.

Flake out

Any flaking or unsound paint must be removed by using mechanical methods, like a 3M Rust and Paint Removal Disc. High-pressure water blasting can also be used. It is not recommended to use wire brushing for this step of the process.

A note on corrosion

Where under-film corrosion is taking place, the existing paint must first be removed (as per the instructions above) and the corrosion products removed, taking care not to damage sound zinc-coated areas, and all paint edges must be feathered to a smooth finish using 180 grit sandpaper.

It is strongly recommended that any badly rusted sections of galvanised steel be replaced. The performance of the subsequent paint systems will be largely dependent on the thoroughness of this surface preparation stage. Immediately spot prime bare areas with one or two coats of Resene ArmourX GP Metal Primer.

Prime and paint

Once all your preparation is complete, apply one full coat of Resene Pre-Coated Steel Primer to the COLORSTEEL® roof. No primer is needed for sound existing acrylic-painted roofs. (although any bare areas should be spot primed with Resene Galvo One galvanised steel primer or Resene ArmourX GP Metal Primer).

Leave for a day, then apply the first coat of Resene Summit Roof, making sure to use a  Resene CoolColour formula for darker shades, and mix in Resene Hot Weather Additive on warmer days to help slow the drying time.

How to choose a paint colour

Often your roof colour will be a darker extension of the colour palette you’ve used on your exterior walls and trim. If you’ve chosen a neutral colour palette for your walls and trim, the roof may be the perfect place to inject a splash of colour. A rich red roof such as Resene Rustic Red looks excellent on a villa or cottage, while a moody blue such as Resene Coast could bring the wow factor to a recent build.

Depending on dry times, a second coat could be applied that same day, as long as there are a few hours of good sunlight left before the dew point of that day – otherwise apply the final coat the following day.

Top tips for painting your roof

• Consult our paint calculator below before you begin the job to ensure you purchase enough paint for the job. 
• Avoid painting in direct sunlight. 
• Continue to mix the pail of paint before decanting to ensure even colour throughout the project. 
• If in doubt about the adhesion of the previous coating, do a scratch test. If paint comes away, more preparation is required for a long lasting paint finish.
• Always have a friend help with this job for practicality and safety.
• Use safe ladders and at height equipment. 
• Do section by section – don’t look at the whole roof as a one-day project. 
• Consider using Resene Umbrella Additive if you’re worried about the forecast and if you are under time pressure

Advice note

On a more serious note, falls from roofs are one of the most common causes of injuries around the home. Professional contractors are required to take stringent safety precautions such as providing edge protection. These steps are not legislated for homeowners. Notwithstanding, this care is required to remain safe while working at heights. Any wet surface is inherently more slippery than a dry surface so wet roofs while cleaning them and stepping onto wet paint present real issues, even to the most careful DIY homeowner.

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