Flashing and lap marks are two of the most common complaints after painting a wall, and the good news is they're almost always fixable. Flashing refers to uneven sheen or dull patches where the paint looks inconsistent, while lap marks are visible ridges or lines left where wet paint overlapped dried paint. Both problems usually come down to technique, timing, or product choice — and with the right approach, you can get a smooth, even finish.
What Causes Flashing and Lap Marks?
Understanding the cause helps you fix the problem properly and avoid it next time.
- Lap marks happen when you paint over an edge that has already started to dry. The dried edge creates a raised ridge that shows through the finished coat.
- Flashing is often caused by uneven porosity in the wall surface — for example, patched areas absorbing paint differently from the surrounding surface — or by applying paint too thinly in some areas.
- Both problems can be made worse by painting in direct sunlight, hot or windy conditions, or using a roller with the wrong nap thickness.
- Low-quality paint or paint that has been over-thinned can also contribute.
Step 1 — Let the Paint Cure Fully
Before you do anything, wait. Trying to fix lap marks or flashing while the paint is still fresh will almost always make things worse. Most interior water-based paints are touch-dry within an hour or two, but they need at least 24 hours (sometimes longer in humid NZ conditions) before you sand or recoat. Check the manufacturer's data sheet for your specific product — brands like Resene and Dulux publish full technical data on their websites.
Step 2 — Assess the Severity
- Mild flashing or slight sheen variation: A single well-applied topcoat may be enough to even things out.
- Visible lap ridges: These need to be sanded back before recoating, otherwise the new coat will simply follow the same ridges.
- Severe flashing over patched areas: The patch may need a coat of sealer or primer before repainting.
Step 3 — Sand Back the Affected Area
For lap marks, lightly sand the affected area with 180–220 grit sandpaper or a fine sanding sponge. The goal is to knock back the raised ridge, not to remove all the paint. Work gently in a circular motion, then feather the edges outward so there's no hard boundary between the sanded and unsanded areas.
Wipe away all dust with a damp cloth and allow the surface to dry completely before painting.
Step 4 — Prime Patched or Porous Areas
If flashing is caused by a repaired area (filled holes, skim-coated patches, etc.), apply a coat of water-based primer or a dedicated sealer to those spots before repainting. This evens out the porosity so the topcoat absorbs consistently. Wattyl and Resene both offer suitable interior primers for this purpose. Allow the primer to dry fully per the product instructions.
Step 5 — Repaint Using Good Technique
This is where most lap marks originate, so technique matters:
- Work in sections and always maintain a wet edge. This means moving quickly enough that you're always blending into paint that hasn't started to dry.
- Roll in a 'W' or 'M' pattern, then back-roll to even out the paint without lifting it.
- Avoid stopping mid-wall. Plan your breaks at natural breaks in the surface (corners, door frames, etc.).
- Use a roller sleeve with the correct nap — typically 10–12 mm for smooth interior walls, 15–20 mm for textured surfaces.
- Don't overload the roller, and don't press too hard. Let the paint flow on rather than forcing it.
- Paint in cooler, stable conditions where possible. The BRANZ guidelines recommend avoiding painting in temperatures above 35°C or in direct sunlight, as paint dries too fast to blend properly.
Step 6 — Apply a Full Recoat if Needed
If the flashing or lap marks are widespread, the most reliable fix is to repaint the entire wall from corner to corner rather than spot-patching. Spot repairs almost always show, especially in raking light. Use the same paint (same batch if possible), and apply it in one continuous session so you maintain a wet edge throughout.
Choosing the Right Paint Finish
Flat and low-sheen paints are far more forgiving of lap marks and application inconsistencies than semi-gloss or gloss finishes. If you're repainting a wall that's prone to showing marks, consider stepping down to a low-sheen or matte finish. Higher-sheen paints require more careful application and are generally better left to experienced painters.
Preventing the Problem Next Time
| Common Mistake | Better Practice |
|---|---|
| Stopping mid-wall for a break | Plan breaks at corners or natural edges |
| Painting in hot sun or wind | Paint in the morning or on overcast days |
| Skipping primer on patches | Always prime repaired areas first |
| Overloading the roller | Load lightly and back-roll evenly |
| Using old or poor-quality paint | Use a quality paint suited to the surface |
When to Call a Professional
If you've repainted the wall twice and the flashing or lap marks are still visible, it may be time to bring in a qualified painter. Persistent flashing can sometimes indicate a deeper issue — such as moisture in the wall, an incompatible paint system, or a surface that needs professional preparation. A licensed painter will be able to diagnose the problem and apply the right solution efficiently. You can find experienced local painters on tradedirectory.co.nz.
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