Exterior cleaning looks simple on the surface. Many homeowners assume it’s just a matter of spraying water, scrubbing a few stains, and moving on. But in reality, incorrect exterior cleaning causes more damage to homes than neglect itself.
Every year across New Zealand, homes suffer premature paint failure, water intrusion, cracked concrete, damaged timber, broken window seals, and roof issues — not because they weren’t cleaned, but because they were cleaned incorrectly.
This guide breaks down the most common exterior cleaning mistakes, explains why they’re dangerous, and shows how professional methods like soft washing, controlled water blasting, and targeted treatments protect your home and save thousands in long-term maintenance.
Why Exterior Cleaning Mistakes Are So Expensive
Your home’s exterior is made up of multiple materials, each with different tolerances:
- Painted cladding
- Stucco and plaster systems
- Fibre cement
- Weatherboards
- Brick and block
- Concrete and exposed aggregate
- Timber decks
- Roof tiles and metal roofing
- Gutters and downpipes
Using the wrong cleaning method on even one surface can lead to:
- Paint stripping
- Water forced behind cladding
- Timber swelling and rot
- Roof leaks
- Cracked concrete
- Permanent surface etching
- Accelerated mould regrowth
Most of these problems don’t appear immediately — they show up months later, long after the damage is done.
Mistake #1: Using High Pressure on House Walls
This is the single most damaging exterior cleaning mistake.
High-pressure washing is not suitable for:
- Painted walls
- Stucco or plaster
- Fibre cement
- Weatherboards
- Modern cladding systems
Why It’s Dangerous
High pressure can:
- Strip paint and protective coatings
- Force water behind cladding
- Damage weather seals
- Crack plaster systems
- Cause hidden moisture issues
Many homeowners mistake a temporarily “clean” look for a successful job — but the damage often appears later as bubbling paint, damp patches, or mould inside the home.
The Correct Method
Soft washing uses low pressure combined with detergents to kill mould and lift dirt safely, without forcing water into the structure.
Mistake #2: Confusing Water Blasting With Soft Washing
Pressure washing and soft washing serve very different purposes, yet they’re often used interchangeably.
Water Blasting Is For:
- Driveways
- Paths
- Patios
- Concrete
- Pavers
- Brick walls
Soft Washing Is For:
- House walls
- Roofs
- Soffits and fascia
- Window frames
- Fences
Using pressure where soft washing is required can permanently damage surfaces. Using soft washing where pressure is needed can leave slippery algae behind.
Knowing the difference is critical.
Mistake #3: Ignoring Mould Root Systems
Many people remove the visible surface mould but ignore what’s underneath.
Why This Fails
Mould, algae, and lichen have root structures that embed into paint, concrete, and roofing materials. Simply rinsing the surface:
- Leaves roots alive
- Causes rapid regrowth
- Makes stains return within weeks
The Correct Approach
Professional cleaning uses detergents or treatments that kill growth at the root, allowing rain and time to wash it away naturally.
This is why soft washing lasts much longer than plain water cleaning.
Mistake #4: Cleaning Roofs With High Pressure
High-pressure roof cleaning causes massive long-term damage.
Common Roof Damage From Pressure Washing
- Tile coatings stripped
- Coloursteel paint damaged
- Water forced under tiles
- Broken ridge capping
- Voided manufacturer warranties
- Shortened roof lifespan
Safe Roof Cleaning Methods
- Moss and lichen treatment
- Soft washing (for suitable roofs)
- Low-pressure application only
Roofs are designed to shed water from above — not withstand pressure from below.
Mistake #5: Skipping Gutter & Downpipe Cleaning
Homeowners often focus on visible surfaces and ignore gutters.
Why This Is Costly
Blocked gutters cause:
- Overflow onto fascia boards
- Water entry into roof cavities
- Foundation erosion
- Interior dampness
- Mould growth inside walls
Gutter cleaning is one of the cheapest exterior services — and one of the most important.
Mistake #6: Using Household Chemicals Incorrectly
DIY cleaners like bleach, vinegar, or harsh degreasers are often misused.
Common Problems
- Bleach lightens stains but doesn’t kill roots
- Vinegar damages paint and seals
- Strong chemicals stain concrete
- Incorrect dilution burns surfaces
- Runoff damages landscaping
Professional detergents are biodegradable, surface-safe, and purpose-designed.
Mistake #7: Over-Cleaning With Excessive Frequency
Cleaning too often can be just as harmful as not cleaning at all.
Examples
- Over-washing paint accelerates wear
- Aggressive deck cleaning causes timber splintering
- Repeated pressure washing weakens concrete
Best Practice
- House washing: annually
- Driveways: every 12–24 months
- Roof treatments: every 2–3 years
- Decks: every 12–18 months
Proper scheduling protects surfaces instead of wearing them down.
Mistake #8: DIY Deck Cleaning With Too Much Pressure
Decks are particularly vulnerable.
Damage Caused by High Pressure
- Raised timber grain
- Splintering boards
- Accelerated rot
- Shortened deck life
Decks should be cleaned using low pressure, controlled flow, and correct direction — never blasted aggressively.
Mistake #9: Failing to Consider Shade & Climate
Different areas of the same home behave differently.
South-Facing Walls
- Stay damp longer
- Grow mould faster
Shaded Areas
- Encourage algae and moss
Coastal Areas
- Accumulate salt residue
Tree-Covered Areas
- Drop organic debris
Cleaning must be adapted to each micro-environment around the property.
Mistake #10: Treating Exterior Cleaning as Cosmetic
Exterior cleaning is often seen as optional — but it’s actually preventative maintenance.
Regular cleaning:
- Extends paint life
- Prevents timber rot
- Protects roofs
- Keeps gutters flowing
- Reduces slip hazards
- Maintains property value
Neglect turns minor issues into expensive repairs.
Why Professional Exterior Cleaning Prevents These Mistakes
Professional services combine:
- Correct pressure control
- Surface-specific methods
- Root-killing treatments
- Safe detergents
- Experience with multiple materials
- Full property assessment
This ensures every surface is cleaned correctly — the first time.
When DIY Cleaning Is Acceptable (And When It’s Not)
DIY May Be Okay For:
- Light surface rinsing
- New concrete
- Small, accessible paths
Professional Cleaning Is Essential For:
- House washing
- Roof cleaning
- Decks
- Stucco or plaster
- Multi-level homes
- Heavy mould or algae
- Gutter and downpipe work
The higher the risk, the more important professional handling becomes.
How to Avoid Exterior Cleaning Damage
Before any cleaning:
- Identify surface type
- Choose the correct method
- Use appropriate pressure
- Apply treatments correctly
- Allow dwell time
- Rinse thoroughly
- Avoid shortcuts
If you’re unsure — don’t guess.
Exterior Cleaning Done Right Saves Thousands
Avoiding these mistakes can prevent:
- Early repainting
- Roof repairs
- Deck replacement
- Internal water damage
- Concrete restoration costs
Correct exterior cleaning isn’t an expense — it’s an investment.
Book Professional Exterior Cleaning With Confidence
If your home exterior needs cleaning — or you’re unsure which method is safe — professional assessment and cleaning will protect your surfaces and your budget.
📞 Call anytime: 0800 997 997
📩 Request a Quote: https://www.metrowaterblasting.co.nz/request-a-quote/