Bubbles forming under joint tape are one of the most common frustrations when stopping plasterboard joints. The good news is that with the right preparation, the correct amount of compound, and proper technique, you can eliminate bubbles almost entirely and achieve a smooth, professional result.
Why Bubbles Form in the First Place
Understanding the cause is the first step to fixing the problem. Bubbles (also called blistering) occur when air becomes trapped between the tape and the plasterboard surface. This usually happens because:
- Too little joint compound was applied under the tape, leaving dry spots
- The tape was pressed down unevenly, trapping pockets of air
- The compound was applied too thinly or had already started to skin over before the tape was embedded
- The tape was applied to a dusty or contaminated surface
- Paper tape was used dry rather than being properly embedded into wet compound
Choosing the Right Tape and Compound
In New Zealand, most interior plasterboard work uses GIB plasterboard systems. GIB recommends using their own stopping compounds and tapes, and it's worth following their system specifications closely — mixing products from different systems can cause adhesion and drying issues.
You have two main tape options:
| Tape Type | Best Use | Bubble Risk |
|---|---|---|
| Paper tape | Flat joints, most interior joints | Low if embedded correctly |
| Fibreglass mesh tape | Corners, repairs, high-movement areas | Slightly higher — needs good compound coverage |
For most flat joints, paper tape embedded in a base coat compound gives the best results. Fibreglass mesh tape is self-adhesive and can be easier for beginners, but it requires a thicker compound bed and is more prone to cracking if not applied correctly.
Step-by-Step: How to Apply Joint Tape Without Bubbles
1. Prepare the Surface
Make sure the joint is clean, dry, and free of dust. Wipe away any loose plasterboard paper or debris. If the board edges are very absorbent, a light mist of water can help, but don't soak them.
2. Apply a Generous Bed Coat
Using a 150 mm broad knife, apply a smooth, even layer of base coat compound directly over the joint. This bed coat should be around 2–3 mm thick — enough to fully embed the tape. Don't skimp here; this is the most common cause of bubbles.
3. Embed the Tape Immediately
Cut your paper tape to length and centre it over the joint. Press it lightly into the wet compound with your fingers to hold it in place, then use your broad knife held at a 30–45 degree angle to firmly draw it along the tape from the centre outward. Apply consistent, even pressure.
4. Skim Off the Excess
After embedding, run the knife along the tape again to squeeze out excess compound from beneath. You want the tape fully wetted and bonded, with just a thin layer of compound visible through the tape surface. If you see dry patches or the tape lifts, apply a little more compound and re-embed.
5. Check for Bubbles Before It Dries
Run your finger or the flat of your knife lightly over the tape. Any bubbles will feel raised. Act quickly — slit the bubble with a sharp knife, inject a small amount of compound, and press flat. Once the compound skins over, you won't be able to fix bubbles without cutting the tape out entirely.
6. Allow to Dry Fully Before Top Coats
Don't rush. Base coats need to dry completely (usually 24 hours, depending on temperature and humidity) before you apply finish coats. New Zealand's humid conditions — particularly in Auckland, Northland, and coastal areas — can significantly extend drying times.
Common Mistakes to Avoid
- Applying tape over dried compound — always embed into wet compound
- Using old or lumpy compound — strain it or replace it
- Working in very cold or damp conditions — compound won't bond well below about 10°C
- Pressing too lightly — you need firm, consistent pressure to push air out
- Skipping the bed coat — never apply tape directly to bare board
Fixing Bubbles That Have Already Dried
If you've already got dried bubbles, you have two options:
- Small bubbles: Score through the bubble with a sharp knife, apply fresh compound, press flat, and feather smooth once dry.
- Large or widespread bubbling: Cut out the affected section of tape entirely, clean the joint back, and re-tape from scratch. It's more work, but a patched bubble will almost always show through paint.
When to Call a Professional
Stopping and finishing plasterboard is a skill that takes practice. If you're working on a large area, a new build, or walls that will be finished with a sheen or semi-gloss paint (which shows every imperfection), it's worth getting a qualified plasterer involved. Poor stopping is very difficult to hide once painted.
Stopping and plastering is not restricted work under the NZ Building Code, so homeowners can legally do it themselves. However, if your plasterboard work is part of a larger project involving structural changes, you may need a building consent — always check with your local council. You can find licensed plasterers and tradespeople in your area at tradedirectory.co.nz.
For health and safety, always work in a well-ventilated space and wear a dust mask when sanding dried compound. Check WorkSafe NZ for guidance on working safely with construction dust.
Master Painters NZ member
