Cracks around door and window frames in new GIB plasterboard are one of the most common complaints in new builds and renovations — but they're largely preventable with the right preparation, products, and technique. Understanding why they form is the first step to stopping them for good.
Why Cracks Form at Frames
The main culprit is differential movement. Timber framing shrinks and moves as it dries out, especially in new construction where framing may still have a relatively high moisture content. GIB plasterboard is rigid, so when the timber frame moves, stress concentrates at the junction between the plasterboard and the door or window frame — and a crack opens up.
Other contributing factors include:
- Inadequate or missing control joints — without a deliberate break, stress has nowhere to go
- Rigid jointing compound applied directly into the corner — hard-set compounds don't flex
- Skipping backing tape — tape reinforces the joint and distributes stress
- Painting too soon — applying paint before the plaster has fully cured can trap moisture and cause movement
- Seasonal humidity changes — New Zealand's varied climate means timber and plasterboard both expand and contract with the seasons
Use the Right Stopping System at Frames
GIB recommends a specific approach for internal angles and frame junctions. Follow their published stopping specifications rather than improvising:
- GIB Grabber screws should be fixed no closer than 12 mm from the board edge at frames, and boards should be cut cleanly so they sit flush without being forced
- Apply GIB Tradeset 45 or similar setting-type compound as a base coat, embedding paper tape or fibreglass mesh tape into the wet compound
- Allow each coat to fully dry before applying the next — rushing this is a leading cause of cracking
- Finish with a flexible acrylic-based finishing compound rather than a hard-set compound in the final coat at frame junctions
Consider Flexible Sealant Instead of Stopping Compound
At the direct junction between GIB and a door or window frame (the shadow line or rebate), many experienced plasterers recommend not filling with stopping compound at all. Instead:
- Leave a 2–3 mm gap between the board edge and the frame
- Once stopping and painting are complete, fill this gap with a paintable flexible acrylic sealant (sometimes called a gap filler or flexible caulk)
- Tool it smooth and paint over once skinned
This approach allows the frame and board to move independently without cracking. Products from Sika and other manufacturers offer suitable paintable acrylic sealants — always check the product datasheet confirms it is paintable and suitable for interior use.
Tape and Coat Properly
Proper tape embedding is non-negotiable at stress points:
| Step | What to do |
|---|---|
| 1. First coat | Apply compound, embed paper tape, feather edges |
| 2. Dry fully | Allow 24 hrs minimum (longer in humid NZ conditions) |
| 3. Second coat | Sand lightly, apply wider coat, feather further |
| 4. Third coat | Fine finish coat, sand smooth when dry |
| 5. Sealant | Apply flexible sealant at frame junction last |
In damp or humid conditions — common in many parts of New Zealand — drying times can be significantly longer. Never rush the process with heat guns or fans blowing directly on wet compound, as this causes surface cracking.
Control Moisture in the Framing
If you're involved in the build from the start, push for kiln-dried or well-seasoned framing timber. BRANZ research consistently shows that high-moisture framing is a primary driver of plasterboard cracking in new homes. If framing is wet, allow it to dry as much as possible before lining.
Also ensure the building is weathertight before GIB is fixed — water ingress after lining causes swelling, movement, and cracking that no amount of stopping technique will fix.
Priming and Painting
Once stopping is complete, apply a quality sealer/primer before topcoats. This stabilises the surface and reduces the risk of paint pulling moisture unevenly from the compound. Resene and Dulux both offer interior primers suited to new plasterboard — check their product guides for the right choice.
Allow the primer to fully cure before applying topcoats, and use low-sheen or flat paints in areas where minor imperfections are more visible, as high-sheen paints highlight any surface irregularities.
When to Call a Professional
While a competent DIYer can handle basic stopping and painting, achieving a Level 4 or Level 5 finish (the standard expected in most NZ homes) around frames takes real skill and practice. If you're seeing cracks in an existing home that keep returning after repair, this may indicate ongoing structural movement, a framing issue, or even moisture ingress — all of which warrant a professional assessment.
A licensed plasterer will have the tools, compounds, and experience to diagnose the root cause and apply a durable fix. You can find qualified local plasterers on tradedirectory.co.nz. For any concerns about structural movement or building envelope issues, consult a Licensed Building Practitioner.
Safety note: When sanding stopping compounds, always wear a P2 dust mask. Stopping compounds may contain silica — check the Safety Data Sheet and refer to WorkSafe NZ guidance on respirable dust.
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