Why is my exterior paint peeling?

The short answer: water behind the paint, or paint that never stuck

Peeling exterior paint traces back to water or poor grip. Dulux's exterior problem solver for peeling lists moisture seeping through uncaulked joints, worn caulk or leaks in the roof or walls. It also lists poor surface prep and lower quality paint.

Then there's grip. Dulux's technical note on adhesion loss says dirt, dust, salt, mould or any loose or powdery layer makes it hard for paint to stick, and that even high quality paint can fail on a dirty surface. Salt matters on the Coast. A Queensland Government painting note says peeling between coats often turns up on eaves, because rain doesn't rinse them often and salt from the air builds up. Paint over that and the new layer peels.

Then there's age. As paint gets older it gets less flexible, so it copes worse as the wall swells and shrinks, according to Dulux. That's when hairline cracks turn into flakes. Taubmans says Australia's harsh sun, heat and changing weather can make exterior paint crack and peel faster than expected. How long a paint job should last out here is its own question, covered in our guide to exterior paint lifespan.

Peeling, blistering, flaking or chalking: what you're looking at

These four failures look alike from the driveway, but each one has a different first thing to check. Here's how to tell them apart, based on how Dulux and the Queensland Government describe each one.

Some chalking isn't a failure. Dulux says some chalking is a normal way for paint to wear. It turns into a problem when it's heavy, or when someone paints straight over it without washing it off. A Queensland Government note says heavy chalking and visible defects are the signal that maintenance is due. Rendered walls have a few extra quirks, covered in our guide to painting rendered walls.

Cause by cause, with a simple check

Each cause of peeling paint has a quick check you can do from the ground. Work down this list before you buy a single tin.

• Water getting in. Look for peeling next to joints, cracked caulk, or under a roof or wall leak. If that's where it starts, Dulux says to find and fix the moisture before you touch the paint.
• Blisters. Cut one open with a sharp blade. The Queensland Government painting note says that if you can see the bare surface underneath, it's probably moisture. If you see another layer of paint, it's more likely solvent blistering. That's more common with dark paints, and not painting in direct sun helps prevent it.
• Wet weather too soon. Dulux lists dew, high humidity or rain shortly after the paint dries as a cause of blistering, especially with poor prep. Timing matters, so see the best time to paint a house exterior.
• Chalk underneath. Rub a dry hand over a sound part of the wall. Dulux uses the same hand test. Powder on your palm means the chalk has to be washed off, then primed or sealed if some stays behind.
• Gloss underneath. If the paint has come away from an older shiny coat, it may not have been sanded first. Dulux lists painting over high gloss without sanding as a prep failure, and Taubmans says to sand back rough or glossy sections.
• Sun and heat. Compare your sunniest wall with your shadiest one. Dulux says darker paints absorb more UV and heat, which puts more stress on the paint and the wall underneath.
• Soft timber. Press a screwdriver into the board where the paint's lifting. If it sinks in, the timber is soft, and Dulux lists weathered, unsound timber as a reason paint fails.

Soft timber is a repair job before it's a paint job. That's why we price weatherboard that needs timber repair first differently to a render repaint.

Can you paint over peeling paint? Not until the loose paint is off

You can't paint over peeling paint and expect it to last. The new coat is only as good as the layer it sits on. Dulux's adhesion note says it's unreasonable to expect a coating to stay stuck when it goes straight over unsound paint, and that paint which is blistering, cracking, flaking or peeling should be completely removed.

How far you go depends on how deep the damage is. Dulux says cracking that hasn't reached the bare surface may be fixed by scraping off the loose paint, sanding the edges smooth, priming bare spots and repainting. Peeling gets the same kind of prep. Loose paint off with a scraper or wire brush, rough spots sanded, bare timber primed. Then a top quality water-based exterior paint over the lot.

Sealing over flaking paint to hold it down doesn't work, for the same reason. A primer grips the layer under it. If that layer is letting go, the primer goes with it. Sound paint is a different story. Dulux says that if little or no chalk remains and the old paint is sound, it can be repainted with a quality exterior paint without a primer.

Built before 1970? Don't scrape or sand anything yet. The Queensland Government says a home built before 1970 has probably got lead-based paint on it, and that lead poisoning can happen when sanders and grinders are used to remove paint. Have the paint tested by a qualified professional first. We test older houses before anyone starts sanding.

When it needs more than a touch-up

A small patch on a ground floor wall, with the cause fixed, is a fair DIY job. Call a painter when any of these apply:

• The peeling is on more than one wall. Dulux warns that isolated failures can be a sign of a wider adhesion problem.
• It's up high. A two-storey home on a slope can need scaffold, and that's a painter's job.
• The house is pre-1970 and the paint hasn't been tested for lead.
• The timber is soft, or the peeling keeps coming back in the same spot.

On a full exterior repaint our prep runs wash, scrape, sand, fill, seal, undercoat. Then Dulux Weathershield or Taubmans All Weather go on as the default. Taubmans backs All Weather with a lifetime guarantee against blistering, flaking and peeling, but only on properly prepared surfaces (terms on the Taubmans site). Most full exteriors take us five to ten working days, depending on access.

Those are guide ranges from our instant estimate, not quotes. Paint in poor condition needs more prep, so the estimate adds 25 percent to the low end and 40 percent to the high end. A two-storey home adds another 20 percent to the low end and 40 percent to the high end. We set the firm price after a free site visit anywhere across the Sunshine Coast. For the full breakdown, read what an exterior repaint costs.