Exterior painting preparation
There are some key points to note when preparing to paint exterior areas. Taking shortcuts or using low quality equipment can cost more time and expenses in remedial work. Using the correct technique will result in a painting job that is faster, cheaper and easier to use than alternative methods.
Exterior – Filling and Patching
Like your interior, starting with a good exterior base is key.
Before painting, remove and replace any rotten or decaying timber. Any holes and cracks in your exterior surface should be filled with a good quality filler such as Polyfilla Exterior Timber. Apply the filler with a putty knife, overfilling to compensate for shrinkage as it sets. Where movement is likely to occur, use a flexible exterior grade filler such as Selleys No More Gaps Exterior & Weatherboard.
Exterior – Masonry and Brick
Prep your masonry and brickwork for painting by scraping away any loose paint. Fill holes with an exterior masonry filler, such as Polyfilla Large Cracks, using a broad-bladed knife or scraper. Using a brush or rag, roughen the filler before it dries completely to match the texture of the surrounding surface.
Exterior – Sanding
If your paintwork is already in good condition, a light but thorough sand should be sufficient.
Any small areas of peeling or cracking can simply be sanded back. Larger holes and defects should be filled and spot primed. If you’re dealing with painted brick or masonry, wash it with a high-pressure cleaner and a stiff bristled brush.
For paintwork and wood all that’s needed is a general purpose sandpaper. For bare metal, a cloth backed emery paper will last longer and get the job done quickly.
Pro tip: if you have a lot of sanding to do, consider using a mechanical sander.
Exterior – Bare Timber & Nail Heads
Before painting, any timber that has been exposed to the elements for more than four weeks should be sanded back to a fresh, new surface. A grey or weathered surface makes an unsound base that promotes peeling and flaking. Simply sand the surface back to remove all greyed timber.
Replace old steel nails with galvanised nails for improved strength and durability. Ensure any nails are punched at least 3mm below the surface, then spot prime and filling holes with a flexible wood filler and then sand smooth
Exterior – Tannin Staining
Some common building timbers contain a natural staining material called tannin. Timber tannins can often break up and carry through to the timber’s surface via moisture in the wood.
Dulux Weathershield has superior blocking properties that prevent tannin from bleeding through the paint film.
Exterior – Bare Masonry, Bricks and Cement Sheeting
Before painting any porous surfaces like bare masonry and cement, it’s important to remove all loose material with a stiff brush. Next, prime the surface to improve adhesion and durability. We recommend using Dulux 1 Step Acrylic Primer Sealer Undercoat, or Dulux Prepcoat Sealer Binder if your substrate is particularly powdery.
Cement render, concrete bricks and mortar must be allowed to cure for a minimum of four weeks, and concrete for a minimum of 8 weeks, before painting with an acrylic paint. If you plan to use an oil-based paint, even longer is required.
While it takes time, curing your cement is vital. It protects against excessive moisture loss and makes for strong, sturdy foundations by reducing the chance of cracking.
Exterior – Bare Metal
Ferrous metals like wrought iron and steel are prone to rust. Before painting, ensure they are free of rust by sanding or wire brushing the surface and treating with a Rust Remover. Then use Dulux All Metal Primer before applying the topcoat.
Non-ferrous metals like galvanised iron and and Zincalume should never be painted directly with oil based enamel paints. Instead, prime with Dulux All Metal Primer first.
As for aluminium, copper, brass and stainless steel, paint will not stick directly to them. Instead, prep the surface by scrubbing with a scouring pad and water before wiping down with a clean rag. Then prime the surface with Dulux All Metal Primer before applying the top coat.
Exterior – New Plastic Down Pipes and Spouting
Plastic down pipes and spouting need a clean surface for paint to stick to. Wipe them down with a cloth dampened with turps, then lightly sand to provide a sound key for the paint.
Immediately before painting, wipe down once more with a water dampened rag.
Exterior – Previously Painted Surfaces
Want to freshen up an existing paint job?
Start by testing the paint in several areas. Cut with a sharp knife and press 10 cm or so of adhesive tape firmly across the middle of the cut. Remove the tape quickly. If any pieces of paint come with it, you will need to strip the loose paint off before applying the new top coat.
Exterior – Stripping
If you need to strip back any existing paint, use a heat gun or a chemical stripper such as Selleys Kwik Strip. Only need to strip a small area? A manual or drill mounted wire brush or dry scraper should do the trick.
Exterior – Blistering, Flaking and Peeling
Blistering, flaking and peeling on wooden surfaces is usually caused by moisture trapped beneath the paint. You’ll find that it almost always happens on the north and west sides of the surface as these areas receive the most sunlight. It’s also common with dark colours that have been applied over old paint.
The first thing to do is remove the source of the moisture. Around windows and doors, look for cracks and seal them. When it comes to walls, the problem may be condensation. Ensure the area has adequate air-flow and consider installing additional vents.
Strip back as much paint as possible then sand the surface smooth and prepare it for a new top coat with Dulux 1 Step Acrylic Primer Sealer Undercoat.
Exterior – Chalking
New Zealand’s high UV sunlight means that oil based enamel breaks down over time, leaving a chalky or powdery surface. Before repainting, the chalking should be scrubbed off and the adhesion of the old paint tested.
Exterior – Mould
Remove mould from your exterior surfaces by diluting 1 part Dulux Prep Wash with 1 part water. Ensure your eyes, skin and clothing are well protected, then apply the solution to the mould with a thick scouring pad, brush or broom to any areas that are to be repainted.
Leave the solution on the surface until mould and mildew stains disappear or soften (approximately 10 minutes), then scrub as required before rinsing with water. Persistent mould growth may require repeated treatments.
Exterior – Acrylics or Enamel?
Acrylics are better for most exterior situations than oil based enamels. As enamels age, they become brittle and chalky, causing surface cracks and flakes. Acrylics retain their colour better and provide a longer lasting, more durable finish.
For all exterior painting we recommend Dulux Weathershield. It’s backed by a guarantee that promises it won’t blister, flake or peel for as long as you live in your house.
In the New Zealand sun the paint is touch dry in twenty minutes at 25 degrees and 50% humidity. This means that during the summer months the drying process is accelerated and the chance of flaking increased.
To slow down the drying rate, add Dulux Hot Weather Thinner to the paint at the rate of 50ml per litre. Another good tip for painting in summer is to avoid painting in direct sunlight or onto a hot surface. Follow the shade wherever possible. You can also add up to 5% water to the paint.
Finally – don’t forget about your brushes. Keep two brushes on hand, one in a bucket of water, and alternate between then to stop them drying out.