5 DIY house-washing mistakes we see all the time in Wellington
DIY house washing is fine for the right property. These 5 mistakes turn a $200 weekend job into a $5,000 paint repair.
DIY house washing is fine for the right property, single-storey, safe access, basic equipment.
The 5 mistakes below turn a $200 weekend into a $5,000 paint repair. James fixes about 10 of these every year. All preventable if you know what to avoid.
- 5mistakes James fixes most
- $200typical DIY cost
- $5,000cost when it goes wrong
- 50–80cmsafe wand distance from wall
DIY house washing is a perfectly reasonable Saturday job for single-storey properties with safe access. Most Wellington homes don’t need professional cleaning every time, the question is whether you have the right gear and the right method. We get called in to fix DIY jobs about 10 times a year. The same five mistakes show up over and over.
Mistake 1: Standing too close with the wand
By a long way, the most common DIY mistake.
Right distance
50–80 cm from the surface. Fan spray, broad pattern, even pressure across the boards.
Wrong distance
10–20 cm from the surface. Concentrated jet, visible strip lines, paint micro-fractures.
DIY units run 1,500–2,500 PSI, which is plenty to damage paint if you stand too close. The instinct when something isn’t coming clean is to move closer, exactly the wrong move. The fix is dwell time with chemistry, not more pressure.
Mistake 2: Wand-up under weatherboard laps
Weatherboard sheds water down. Spraying up from below drives water into the cavity between cladding and framing, where it then takes weeks to dry out.
The rule: always spray weatherboard from above or level, never from below. Water needs to follow gravity off the boards, not be forced behind them.
Mistake 3: No chemistry, just water
Mould and lichen are organisms. Water moves them around; chemistry kills them. A water-only DIY wash leaves the moss alive on the surface, and it regrows in 2–4 weeks.
A simple fix: hardware stores sell exterior-cleaning concentrate (Wet & Forget, Spray & Walk Away, similar). Mix at label rates, apply with a garden sprayer, wait 15 minutes, then rinse. That’s how the pros do it; the gear and the chemistry are both available retail.
Mistake 4: Ignoring the roof
Most DIY jobs do the walls and skip the roof, either because the roof is high or because moss isn’t visibly bothering anyone yet.
Problem: moss on roofs is what shortens roof life. Walls are cosmetic; roofs are structural. If you’re going to DIY your exterior, the roof is the one to invest in (either DIY with a long extension wand, or hire out the roof while doing walls yourself).
Mistake 5: Wrong day of the week (and wrong time of day)
DIY washes work better when:
- Overcast but dry. Direct sun dries chemistry too fast before it can work.
- Not the day before rain. Wash today, rain tomorrow = chemistry rinsed off before it had time to dwell.
- Morning start. Gives you all day for the chemistry, dwell, rinse cycle plus drying.
- Mild temperature. Hot days dry too fast; cold days slow chemistry action.
The classic mistake is starting at 2 PM on a Saturday after lunch, finishing in the dark, and going to bed wondering if it worked.
When to call in someone
If any of these apply, DIY isn’t worth it:
- Two-storey property
- Steep hillside section
- Concrete-tile or Decramastic roof needing attention
- Coloured-press concrete driveway
- Heritage timber over 50 years old
- You’d rather not climb a ladder twice in one day
Get a quote, most Wellington jobs come back the same day.
James, Clear Water Blasting.
Written by James · Clear Water Blasting Services
Owner-operated since 2001 from Johnsonville. James does every quote and every job himself across Wellington, the Hutt, Kapiti, Porirua and the Wairarapa.
From the blog
Most recent posts
House washing in Wellington's coastal suburbs, Lyall Bay, Kilbirnie, Seatoun, Island Bay and Miramar
Why coastal Wellington homes age twice as fast, and what to do about it. A practical guide to salt-spray, southerly exposure and the cleaning regime that actually works.
Read →
Soft wash vs water blasting: which does your house actually need?
Same trade, two very different tools. Soft wash protects painted surfaces; water blasting strips them. Knowing the difference matters.
Read →
Moss treatment in Wellington: soft wash, spray, or scrape, which actually works?
Wellington's damp climate grows moss faster than almost anywhere in NZ. Three treatment methods, which one fits your roof and walls, what each costs, and how long results last.
Read →
