Why Timber Joinery Fails – And It’s Usually Not the Joinery
Understanding the Critical Role of Correct Painting on Timber Windows and Doors
By Aaron Dando – Owner, Dando Doors and Windows
At Dando Doors and Windows we manufacture high-quality timber windows and doors designed for New Zealand conditions.
Our joinery is carefully crafted using proven systems and quality materials, and is built to provide many years of reliable service.
However, once our products are installed on site, their long-term durability depends heavily on one final stage:
The quality and completeness of the painting system applied by others.
Over many years we have seen the same pattern repeat:
Well-made timber joinery fails prematurely not because of manufacturing defects, but because essential painting requirements are not followed on site.
The Reality: We Don’t Control the Painter
Every set of joinery we supply includes written care and warranty instructions.
These instructions clearly state what must be done to protect timber joinery from moisture and weather exposure.
But as the joinery manufacturer we do not:
engage the painter
supervise the painter
control their scope of work
apply the coatings ourselves
That responsibility sits with the builder or homeowner.
When those instructions are not followed, the consequences are predictable:
early paint failure
swelling and movement
moisture ingress
deterioration of glazing beads
reduced lifespan of double glazing units
and eventually – timber decay
This is frustrating for everyone involved – particularly when the root cause is avoidable.
Two Critical Painting Requirements That Are Often Missed
There are two simple but essential requirements that protect timber joinery from moisture ingress.
Both are clearly stated in our warranty documentation. Both are supported by NZ standards and industry guidance.
And both are regularly overlooked.
Requirement 1 – Paint Must Overlap Onto the Glass
Our Care, Maintenance and Warranty document states:
“The paint skin should overlap onto the glass 2mm on the exterior surface to ensure a proper seal.”
It also requires:
“A complete waterproof paint skin must be maintained at all times on all edges.”
This overlap detail is not cosmetic – it is functional.
Why the Paint Overlap Matters
The junction where glass meets timber – at the glazing bead – is one of the most vulnerable moisture points in any window or door.
Even with modern glazing tapes and sealants, there is still a fine interface where moisture can sit or slowly track into the timber.
To protect this junction, best practice requires a continuous paint film that bridges from the timber onto the glass.
Paint that stops neatly at the edge of the bead may look tidy, but it leaves a microscopic pathway for water.
This Is Confirmed by Resene Technical Guidance
New Zealand’s leading paint manufacturer Resene advises:
“Ideally, you need to overlap the primer and topcoats up onto the glass by 2–3mm. This provides a watertight seal so moisture cannot get between the glass and putty.”
Although modern joinery uses timber glazing beads rather than traditional putty, the technical principle is identical:
Seal the timber-to-glass junction with a paint overlap.
“But We Don’t Use Putty Anymore”
Correct – and that does not change the requirement.
Whether the interface is:
putty to glass, or
timber glazing bead to glass
…it remains a critical moisture entry point.
The paint overlap requirement applies to both systems equally.
Requirement 2 – Tops and Bottoms Must Be Fully Sealed
The second common failure is even more basic.
Painters frequently omit:
the top edges of doors
the bottom edges of doors
the tops and bottoms of window sashes
Because these areas are not readily visible, they are often left uncoated.
Unfortunately, they are also the areas most prone to moisture uptake.
Industry Guidance Agrees
The Master Painters NZ Association advises that:
“Failing to seal the top and bottom edges of the door is likely to void the door manufacturer’s warranty.”
Unsealed edges are a well-recognised cause of:
swelling
paint breakdown
moisture ingress
premature timber decay
This Is Backed by NZ Building Code and Standards
New Zealand Building Code durability provisions and NZ Standards require that:
Timber components must be protected from moisture
Protective coatings are applied to all surfaces
Finishes are applied in accordance with manufacturer specifications
AS/NZS 2311 – Guide to the Painting of Buildings – reinforces the need for complete coating systems to protect timber joinery from weather exposure.
When coatings are incomplete, the building element is no longer adequately protected.
It Also Affects Double Glazing Warranties
Many people don’t realise that poor painting can also affect the warranty on insulating glass units.
Double glazing warranties generally require that joinery is maintained in accordance with the joinery manufacturer’s standards and care instructions.
Painting is therefore critical not only to the timber, but also to the long-term performance of the glazing.
Why This Is a Difficult Issue for Joinery Manufacturers
We invest significant time and effort producing joinery that is designed to perform for many years.
When painters do not:
overlap paint onto the glass, or
seal tops and bottoms
…the joinery is left unprotected.
Years later, when problems appear, we are often asked to assess issues that are the result of incomplete or incorrect painting, not manufacturing defects.
What Builders and Homeowners Need to Ensure
If you are responsible for painting timber windows and doors, it is essential to ensure the following:
At the glazing bead:
Primer, undercoat and topcoats extend onto the glass by approx. 2mm
A continuous paint film bridges timber to glass
This applies to modern timber glazing beads as well as traditional putty systems
On doors and sashes:
Tops and bottoms are fully sealed
All six faces are coated
No raw timber edges remain
General requirements:
Coatings applied in accordance with AS/NZS 2311
Manufacturer specifications followed
Quality exterior-grade paint systems used
Our Position
At Dando Doors and Windows we stand fully behind the quality of our manufacturing.
However, we cannot be responsible for:
painting carried out by others
incomplete or incorrect coating systems
instructions that are not followed
Timber joinery will only perform as well as the protection applied to it.
Our Recommendation
To ensure long-term durability and full warranty protection:
Overlap paint onto the glass by approximately 2mm at all glazing beads
Fully seal tops and bottoms of all doors and window sashes
Follow our written painting instructions in full
These are small details, but they have a major impact on performance and lifespan.
Need Advice?
If you are unsure about:
correct painting requirements
warranty conditions
maintenance obligations
best practice for timber joinery
…please contact us before painting begins.
We are always happy to help clarify what is required.
📍 Auckland showroom
🚚 Nationwide
🧾 Free estimates & technical guidance
Browse: