Why 80% of Paint Failures Start Before You Open the Tin

I'm going to tell you something that might save you thousands of dollars: the actual painting is the easy part.

After 14 years painting homes across Central Otago, I can tell you with certainty that 80% of the work happens before any paint touches your walls. And 80% of paint failures? They happen because someone skipped the prep.

Last summer, I got called to a Queenstown property where the paint was peeling in sheets - just 18 months after a "professional" job. The painter had used quality Resene Lumbersider. Applied it properly. Good weather conditions.

But they'd painted over chalky, dirty weatherboards. Skipped the primer on bare patches. Didn't fix the gaps where moisture was getting in.

That homeowner paid twice for one paint job.

This guide is everything I know about preparing a New Zealand home for exterior painting - the steps that separate a paint job that lasts 15 years from one that fails in two.

Before You Start: Is Your House Actually Ready to Be Painted?

Not every house should be painted right away. Before you commit time and money, walk around your property and answer these questions:

1. Is there active water damage?

Look for:

• Soft or spongy weatherboards (poke them with a screwdriver)
• Black mould that keeps coming back
• Peeling paint that's bubbling from underneath
• Staining below windows or gutters

If yes: Fix the water source first. Painting over active moisture problems is throwing money away.

2. What's the condition of your existing paint?

Run your hand over the painted surface. If it comes away chalky (like white powder on your fingers), the paint has broken down and won't hold new paint without proper preparation.

3. Is the timber sound?

In Central Otago, we see a lot of:

• UV-damaged timber on north-facing walls
• Frost damage on south-facing areas
• Rot around windows and at the bottom of weatherboards

Minor surface damage can be prepped and painted. Structural damage needs repair first.

4. Pre-1970s home?

There's a good chance you have lead paint. This requires specific handling - not a DIY job unless you're trained. Get it tested before you start scraping.

The Complete Exterior Prep Process: Step by Step

Step 1: Set Up Your Work Area Properly

Time required: 1-2 hours

Before you touch the house, protect everything around it. Paint prep is messy - old paint chips, dust, cleaning solutions, and water go everywhere.

What to do:

• Cover your garden: Use breathable canvas drop cloths over plants, not plastic. Plastic in direct sun will cook your plants in hours.
• Protect your deck: Old paint chips and cleaning chemicals will stain timber decking permanently.
• Cover outdoor furniture: Or better yet, move it away from the house entirely.
• Remove items from walls: Light fixtures, house numbers, mailbox brackets, security cameras. Don't try to paint around them.
• Close windows and doors: Keep them shut during washing and sanding to prevent dust getting inside.

Pro tip: Take photos of where everything was mounted. You'll thank yourself when you're reattaching fixtures at the end.

Step 2: Wash the Entire Exterior

Time required: Half a day to full day (depending on house size)

Paint doesn't stick to dirt. It doesn't stick to mould. It doesn't stick to the fine layer of Central Otago dust that coats everything. The house must be clean.

You'll need:

• Pressure washer (hire from Hirepool for $80-120/day)
• House wash solution (30 Second Outdoor Cleaner, $35-40)
• Long-handled scrub brush for stubborn areas
• Garden hose for rinsing

The process:

1. Mix your cleaning solution according to the instructions. More isn't better - too strong and you'll damage timber.

2. Start from the top and work down. Wet the walls, apply the cleaning solution, let it sit for 10-15 minutes (don't let it dry).

3. Pressure wash from top to bottom. Keep the nozzle moving and maintain a consistent distance. Too close = damaged timber. Too far = ineffective cleaning.

4. Watch your pressure. For weatherboards, stay under 2000 PSI. For rougher surfaces, you can go higher.

5. Pay special attention to:

   • Under eaves (where spiders and cobwebs live)
   • South-facing walls (where moss and mould grow)
   • Around windows (where dirt accumulates in corners)
   • Bottom boards (where splashback from the ground deposits dirt)

Critical for New Zealand: Our UV breaks down paint into a chalky powder. You need to remove this chalking completely, or new paint won't adhere. If areas still feel chalky after washing, scrub them manually with a stiff brush.

Drying time: Wait at least 2-3 days of dry weather before moving to the next step. In Central Otago's dry climate, you might get away with 48 hours in summer. In Dunedin or coastal areas, allow longer.

Step 3: Inspect and Assess the Damage

Time required: 2-3 hours

Now that the house is clean, you can actually see what you're dealing with. Walk around with a notepad and categorise everything you find.

What you're looking for:

Peeling or flaking paint:

• Small areas (under 1m²) = scrape and sand
• Large areas (over 1m²) = might need complete strip
• If paint is peeling in sheets = adhesion failure, need to identify why

Bare or exposed timber:

• Note locations for spot priming later
• Check if timber underneath is sound or damaged

Soft or rotten timber:

• Poke suspect areas with a screwdriver
• If it goes in easily, the timber is compromised
• Small areas can be filled, large areas need replacement

Gaps and cracks:

• Around windows and door frames
• Between weatherboards
• Where trim meets walls
• At corners and junctions

Nail holes and fastener issues:

• Popped nails that need resetting
• Rusted nail heads bleeding through paint
• Missing or damaged flashings

Mould or mildew:

• Black spots that survived the wash
• Areas that stay damp longer than others

Make a list and prioritise: What must be fixed before painting? What can wait? What needs professional assessment?

Step 4: Remove Loose and Failing Paint

Time required: 1-3 days (depending on condition)

This is the hard work. There's no shortcut. Paint won't stick to loose paint, so every bit of failing coating needs to come off.

You'll need:

• Paint scraper (carbide blade stays sharp longer - Bahco from PlaceMakers, about $45)
• Heat gun for stubborn areas (hire from Kennards, $40-50/day)
• Sanding block and various grits (60, 80, 120)
• Orbital sander for large areas (hire for $80-100/day)
• Dust mask (P2 rating minimum)
• Safety glasses

The process:

1. Scrape all loose paint - work with the grain, not against it. You're removing paint that's already failed, not creating new damage.

2. Focus on edges - where good paint meets bad paint, you need to create a smooth transition. No sharp edges or ridges.

3. Use heat carefully - the heat gun softens old paint for easier removal. Keep it moving to avoid scorching timber.

4. Sand the transitions - where you've scraped back to bare wood, the edge between old paint and bare timber needs to be feathered smooth. Start with 60-grit, finish with 120-grit.

What you're NOT trying to do: Remove all old paint. If it's firmly adhered and in good condition, leave it. You're only removing what's failing.

Central Otago specific: Our dry climate means paint tends to crack and peel more than it flakes. Look for the fine "alligator skin" cracking pattern that indicates paint breakdown - this needs removal even if it seems stuck.

Step 5: Make Repairs

Time required: 1-2 days (depending on damage)

Now you fix everything you found in your assessment.

For small areas of rot (under 50mm):

1. Scrape out all soft material until you hit solid wood
2. Treat with a wood hardener (Selleys Wood Rot Hardener, $25)
3. Fill with exterior wood filler (Selleys Knead It, $20-30)
4. Allow to cure completely (check product instructions - usually 24 hours)
5. Sand smooth

For larger rot or structural damage:

This is where you need to make a call. Replacing a weatherboard or section of trim is better than patching something that'll fail again. If you're not confident, get a builder to assess.

For nail pops and fastener issues:

1. Reset popped nails below the surface
2. Punch all nail heads slightly below the surface
3. Fill holes with exterior filler
4. For rusted nail heads, apply rust converter first

For gaps and cracks:

Use paintable exterior caulk (Selleys No More Gaps, Sikaflex) for:

• Gaps around window and door frames
• Cracks between weatherboards
• Joints where trim meets walls
• Any gap where water could penetrate

Apply caulk neatly, tool with a wet finger, and wipe excess immediately. Messy caulk looks amateur.

Do NOT caulk:

• The bottom edge of weatherboards (they need to breathe and drain)
• Weep holes in window frames
• Any gap that's intentionally there for ventilation

Step 6: Sand All Surfaces

Time required: 1-2 days

Even surfaces that don't need paint removal need sanding to create a key for new paint.

The purpose of sanding:

• Creates "tooth" for new paint to grip
• Removes any remaining chalking
• Smooths transitions between repairs and existing paint
• Removes any remaining gloss from old paint

What to use:

• 80-120 grit for general scuff sanding
• 60-80 grit for smoothing filler and repairs
• Orbital sander for large flat areas
• Hand sanding for detail work and corners

Technique:

• Sand with the grain, never against
• Keep the sander moving - don't dwell in one spot
• Wipe dust off regularly so you can see what you're doing

After sanding:

The house is now covered in fine dust. This must be removed before priming. Use:

• Leaf blower to remove bulk dust
• Soft brush on all surfaces
• Damp rag (not wet) for final wipe-down
• Allow to dry completely

Step 7: Prime Bare and Problem Areas

Time required: Half day to full day

Primer is the bridge between your substrate and your topcoat. It's not optional.

Where you must prime:

• All bare timber (new or exposed by scraping)
• Repaired areas (filler, wood putty, new timber)
• Stain-blocked areas (tannin bleed from cedar/rimu, old stains)
• Areas where you're changing dramatically from dark to light colours
• Galvanised metal (gutters, flashings) that will be painted

Primer selection for New Zealand conditions:

For most exterior timber:

• Resene Wood Primer (oil-based) - excellent adhesion, blocks tannin
• Dulux 1 Step Prep (water-based) - easier cleanup, good all-rounder

For problem areas:

• Resene Sureseal - stain blocking, good for tannin bleed
• Zinsser B-I-N (shellac-based) - heavy-duty stain blocking

For bare timber in Central Otago: I prefer oil-based primers on exterior wood in our climate. They penetrate better and provide more durable adhesion. Yes, cleanup is harder. Yes, they smell. The results are worth it.

Application:

• Apply primer generously to bare timber - it should soak in slightly
• Feather edges where primer meets existing paint
• Two coats on end grain (cuts, edges) where timber absorbs more
• Allow full cure time before topcoat (usually 24 hours, longer in cool weather)

Step 8: Final Inspection and Touch-Ups

Time required: 2-3 hours

Before you start painting, walk the entire house one more time.

Check for:

• Any spots you missed during prep
• Primer that didn't cover properly (needs second coat)
• Dust or debris that's settled since cleaning
• Caulk that's cracked or pulled away
• Any repairs that need final sanding

Also check:

• Windows are properly masked or taped
• Door hardware is removed or protected
• Drip edges and weatherboards are clean underneath
• Gutters and downpipes are protected if not being painted

Weather check:

Don't start painting unless you have:

• Minimum 48 hours of dry weather forecast
• Temperatures between 10-25°C
• Humidity below 85%
• No strong winds forecast

In Queenstown/Wanaka, this typically means painting season runs November through March, with occasional windows in October and April.

Timeline: How Long Does All This Take?

For a typical 3-bedroom weatherboard home in average condition:

Total: 6-10 days of work, spread over 2-3 weeks (allowing for drying time)

This is why professional painters charge what they do. Prep is time-intensive, physically demanding, and absolutely critical.

Tools and Materials Checklist

Equipment (Hire)

• Pressure washer (2000+ PSI)
• Orbital sander
• Heat gun (for stubborn paint)
• Extension ladders
• Scaffolding (for two-storey homes)

Equipment (Buy or Own)

• Paint scrapers (various sizes)
• Sanding blocks and paper (60, 80, 120, 180 grit)
• Wire brush
• Caulking gun
• Brushes for primer (50-75mm)
• Rollers for primer (10-13mm nap)
• Drop cloths
• Masking tape
• Safety gear (dust mask P2, safety glasses, gloves)

Materials

• House wash solution
• Exterior wood filler
• Paintable exterior caulk
• Wood hardener (for rot treatment)
• Exterior primer (oil-based for bare timber)
• Stain-blocking primer (for problem areas)

Estimated Cost (DIY)

For a typical 150m² home in average condition:

• Equipment hire: $300-500
• Materials: $400-600
• Total prep cost: $700-1,100

This doesn't include the paint itself - that's a separate calculation. But it shows you where your money goes when you hire a professional: mostly labour.

When to Call a Professional

Prep is DIY-friendly for most homeowners who are:

• Comfortable working on ladders
• Physically capable of manual labour
• Patient enough to do it properly
• Working on a single-storey home in reasonable condition

Call a professional if:

• Your home is two-storey or has difficult access
• You suspect lead paint (pre-1970s homes)
• There's significant rot or structural damage
• The existing paint is failing severely (multiple coats, complete adhesion failure)
• You simply don't have the time to do it properly

A professional will prep faster, identify problems you might miss, and know exactly what products and techniques work in your local conditions.

In the Queenstown/Wanaka area:

• Painters Wanaka handles everything from prep through to final coat
• Little Dog Decorating offers full exterior services in Queenstown

The Prep Mistakes That'll Cost You

After 14 years, I've seen every shortcut and every failure. Here's what not to do:

1. Painting over dirt or mould - Paint will peel within months. Always wash first.

2. Skipping the primer on bare timber - Paint soaks into unprimed timber unevenly, leading to patchy coverage and early failure.

3. Painting in the wrong conditions - Too cold, too hot, too humid, or rain coming = paint failure.

4. Not removing chalky old paint - New paint can't bond to chalking. It'll peel in sheets.

5. Caulking gaps that should breathe - Trapped moisture causes rot. Some gaps are intentional.

6. Rushing the drying times - Whether it's after washing or between primer coats, patience is required.

7. Ignoring the south side - In NZ, north gets UV damage, south gets moisture and mould. Both need attention.

Final Thoughts: Prep Is Where Paint Jobs Are Won or Lost

I know this guide is long. I know the process seems like a lot of work. But here's the truth:

The difference between a paint job that lasts 5 years and one that lasts 15 years is almost entirely in the preparation.

Do it right, do it once. Skip it, and you'll be doing it again in half the time - at twice the cost.

Got questions about prepping your specific property? Drop a comment below or get in touch. I'm always happy to help Kiwi homeowners protect their biggest investment.

Cheers, Brad

Related Reading

• What I've Learned Painting Weatherboard Homes Across Otago for 14 Years
• A Kiwi's Guide to Picking the Right Primer
• The Kiwi Guide to Sorting Out Peeling or Bubbling Paint
• DIY or Hire a Pro? The Honest Cost Breakdown