Bubbling or blistering paint is one of the most frustrating things to discover on your freshly painted walls or weatherboards. The good news is that it's usually fixable with the right approach — and understanding why it happened is the key to making sure it doesn't come back.
What Causes Paint to Bubble?
Paint bubbles (also called blisters) form when the paint film lifts away from the surface beneath it. There are several common culprits:
- Moisture — The number one cause in New Zealand homes. Water vapour pushing through walls, condensation, or painting over a damp surface all cause the paint film to lose adhesion.
- Heat — Painting in direct sunlight or on a hot surface causes the outer layer of paint to dry too quickly, trapping solvents underneath.
- Poor surface preparation — Painting over dirty, oily, dusty, or glossy surfaces prevents proper adhesion.
- Incompatible products — Applying water-based paint directly over an oil-based undercoat (or vice versa) without the correct primer can cause delamination.
- Applying paint too thickly — Heavy coats trap solvents that need to escape as the paint cures.
- Old or failing paint — If the existing paint is already peeling or chalking, new paint applied on top will bubble along with it.
In New Zealand's varied climate — from the humid north to the cold, damp south — moisture is by far the most common trigger. BRANZ research consistently identifies moisture management as critical to paint durability on NZ homes.
How to Diagnose the Type of Bubble
Before you reach for the scraper, work out what type of blister you're dealing with:
| Bubble type | Likely cause | What you'll find inside |
|---|---|---|
| Appears soon after painting | Solvent trapped / heat | Dry inside |
| Appears weeks or months later | Moisture from behind | Damp or wet inside |
| Only on exterior | Weather exposure or sun | Dry or damp |
| Only in wet areas (bathroom, kitchen) | Condensation / steam | Damp inside |
If the bubble is damp inside, you must find and fix the moisture source before repainting — otherwise the problem will return no matter how well you prep.
Step-by-Step: How to Fix Bubbling Paint
1. Find and fix the moisture source
Check for leaking pipes, blocked gutters, inadequate ventilation, or rising damp. In bathrooms and kitchens, make sure extractor fans are working properly. Healthy Homes standards (relevant to rental properties) also require adequate ventilation — see Tenancy Services for details.
2. Allow the surface to dry completely
Do not rush this step. Depending on the extent of moisture, this could take days or even weeks. Use a moisture meter if you have one — most hire shops stock them.
3. Scrape and sand back
Using a broad-bladed scraper, remove all loose and bubbled paint back to a firm edge. Sand the area smooth with medium-grit sandpaper (around 80–120 grit), feathering the edges so there's no hard lip.
4. Clean the surface
Wipe down with a damp cloth to remove dust, then allow to dry. If there's any grease or mould, treat it first — a diluted bleach solution works for mould, but let it dry fully before proceeding.
5. Apply a suitable primer
This is a step many DIYers skip — don't. A good adhesion primer seals the bare substrate and gives your topcoat something to grip. For bare timber, use a timber primer. For plasterboard or plaster, use a water-based sealer. Resene and Dulux both offer primers suited to NZ conditions — ask in-store for the right product for your substrate.
6. Repaint in suitable conditions
Paint when the temperature is between roughly 10°C and 30°C, humidity is moderate, and the surface is in the shade. Avoid painting in direct sun or on windy days. Apply thin, even coats and allow each coat to dry fully before applying the next.
Exterior Paint Bubbling: Extra Considerations
On the outside of your home — particularly on weatherboards, James Hardie fibre cement, or timber — bubbling is often a sign that moisture is getting in from outside or behind the cladding. Check that:
- All caulking around windows, doors, and penetrations is intact
- Flashings are correctly installed
- Paint film thickness is adequate (check the manufacturer's data sheet)
James Hardie provides specific painting guidelines for their products that are worth following to maintain warranties.
Preventing Bubbles in the Future
- Always prepare surfaces thoroughly before painting
- Use quality paint from reputable brands — it pays off in longevity
- Don't paint in extreme heat, cold, or high humidity
- Ensure good ventilation in bathrooms and kitchens
- Use the correct primer for your substrate
- Follow the paint manufacturer's recoat times — don't rush between coats
When to Call a Professional
If bubbling is widespread, keeps coming back, or is linked to a moisture problem you can't identify, it's time to bring in a qualified painter or building inspector. Recurring bubbles on exterior cladding can indicate a weathertightness issue — a serious problem that needs professional assessment. A licensed painter will also know which products and systems comply with the NZ Building Code for your specific situation.
You can find experienced, local painters on tradedirectory.co.nz who can assess the problem and give you a proper fix.