How to prepare walls before painting is the single most important factor in determining whether your paint job looks professional or patchy. Preparation accounts for roughly 70 percent of the total effort in any quality paint job, yet it is the step most commonly rushed or skipped by DIY painters and inexperienced contractors. Proper wall preparation involves inspecting the surface for damage, removing loose or flaking paint, filling holes and cracks with appropriate filler, sanding the entire surface to create a smooth and even substrate, cleaning the wall to remove dust and contaminants, masking edges and protecting surrounds, and priming bare or repaired areas before the topcoat is applied. Skip any of these steps and the paint will show every imperfection, adhere poorly, and fail significantly earlier than it should. At Quality Painting Sydney, thorough wall preparation is built into every project because we know from experience that the finish is only as good as what is underneath it.
Why Preparation Matters More Than the Paint Itself
Paint is transparent in a way most people do not realise until they see the result. Every bump, crack, hole, rough patch, and uneven surface underneath the paint shows through the finished coat. A premium paint applied over a poorly prepared wall looks worse than a mid-range paint applied over a properly prepared one.
This is because paint conforms to whatever is underneath it. It does not fill holes, bridge cracks, or smooth out texture differences. It highlights them. Under certain lighting conditions, particularly raking light from windows or downlights, imperfections that were invisible on the bare wall become glaringly obvious once painted.
“The most common complaint we hear from homeowners who have had a bad painting experience is ‘the walls look worse than before.’ Almost every time, the issue is not the paint or the colour. It is the preparation underneath. The previous painter rushed the prep or skipped it entirely.”
This is why professional residential painters spend more time preparing than painting. The preparation is invisible once the job is finished, but its absence is not.
Step 1: Inspect the Wall Surface
Before anything else, examine every wall surface carefully under good lighting. Look at the wall from different angles, particularly with light raking across the surface from the side, as this reveals imperfections that are invisible when viewed straight on.
What you are looking for includes nail holes and screw pops from picture hooks, shelving, and fixtures. Hairline cracks along joins, corners, and around door and window frames are common in Sydney homes due to building movement and seasonal temperature changes. Dents and gouges from furniture, door handles, and general wear over the years are typical in lived-in spaces. Flaking or peeling paint from previous coats indicates adhesion failure that must be addressed. Water stains from past leaks or condensation suggest moisture damage that needs investigation before painting over. Uneven texture from previous poor repairs, roller marks, or brush strokes from earlier paint jobs creates an inconsistent surface that will show through new paint.
Note each issue and its location. Different problems require different repair approaches, so a thorough inspection saves time by ensuring you fix everything in one pass rather than discovering problems after the first coat has gone on.
Step 2: Remove Loose and Flaking Paint
Any paint that is no longer firmly bonded to the wall must be removed before new paint is applied. Painting over flaking paint is one of the most common preparation mistakes because the new paint bonds to the loose old paint rather than the wall itself. When the old paint continues to peel (which it will), it takes the new paint with it.
Use a paint scraper or putty knife to remove all loose, bubbling, and flaking paint. Work the scraper under the edges of any peeling areas and remove everything that comes away without excessive force. Sand the edges of the remaining sound paint to create a smooth transition between the bare surface and the intact paint layer so there is no visible step or ridge.
For walls with extensive flaking across large areas, the old paint system may have failed completely and the entire wall may need stripping back to the substrate. This is common in older Sydney homes, particularly where oil-based paints were previously used and have become brittle with age. For properties with very old paint layers, check whether lead paint is present before disturbing the surface.
Step 3: Fill Holes, Cracks, and Damaged Areas
Once the loose material is removed, every hole, crack, dent, and gouge needs filling to create a smooth, even surface.
| Damage Type | Best Filler | Application Method |
|---|---|---|
| Small nail holes and pin holes | Lightweight spackling compound | Press into hole with finger or putty knife, wipe smooth |
| Screw holes and medium dents | General purpose wall filler | Apply with putty knife, slightly overfill to allow for shrinkage and sanding |
| Larger holes and gouges | Two-part filler or setting compound | Build up in layers, allowing each to dry before adding the next |
| Hairline cracks | Flexible gap filler or acrylic caulk | Run a bead along the crack, smooth with a wet finger |
| Wider structural cracks | Setting compound with fibreglass mesh tape | Apply tape over the crack, then cover with two coats of compound |
| Damaged plasterboard corners | Corner bead and setting compound | Replace damaged corner bead, then skim with compound |
Apply filler slightly proud of (higher than) the surrounding surface. Most fillers shrink slightly as they dry, and having a small excess allows you to sand back to a perfectly level finish. Underfilling means the depression will still be visible after painting.
Allow all filler to dry completely before sanding. Drying times vary by product and thickness, but as a general rule, give lightweight fillers at least two hours and heavier setting compounds at least four hours or overnight for thicker applications.
Step 4: Sand the Entire Wall Surface
Sanding is the step that transforms a repaired wall into a paintable surface. It serves two purposes: smoothing the filled and repaired areas level with the surrounding wall, and creating a slight texture (tooth) on the existing painted surface so the new paint adheres properly.
For filled areas: Use 120-grit sandpaper to level the dried filler flush with the surrounding wall. Run your hand over the area after sanding. If you can feel any ridge, depression, or texture difference between the filled area and the surrounding surface, it will show through the paint. Sand until it feels completely smooth and seamless.
For the rest of the wall: A light scuff sand with 180 to 220-grit sandpaper or a sanding sponge removes the gloss from the existing paint and creates a mechanical bond for the new coat to grip. This is especially important when painting over previously glossy or semi-gloss surfaces, as new paint does not adhere well to a smooth, shiny surface without this step.
Sand in smooth, even strokes. Avoid pressing too hard in one spot, which creates depressions. For large wall areas, a pole sander or electric orbital sander with dust extraction speeds up the process significantly.
Step 5: Clean the Wall
After sanding, the wall is covered in fine dust that must be removed before priming or painting. Dust sitting on the wall surface prevents paint from bonding to the substrate and creates a gritty, rough finish.
Vacuum the wall using a brush attachment to remove the bulk of the dust. Follow with a damp (not wet) microfibre cloth wiped across the entire surface to pick up any remaining fine particles. Allow the wall to dry completely before proceeding to priming.
For walls in kitchens and bathrooms, additional cleaning may be needed to remove grease, soap residue, and mould. A solution of sugar soap dissolved in warm water is the standard cleaning agent for painted walls. Wipe the wall with the sugar soap solution, rinse with clean water, and allow to dry. For bathrooms with mould history, the best paint finish for bathrooms guide covers how to treat and prevent mould before repainting.
Step 6: Mask and Protect
Before any primer or paint goes on, all edges, fixtures, and surrounding surfaces need protection.
Apply painter’s masking tape along the edges of skirting boards, architraves, window frames, door frames, and ceiling lines. Press the tape edge down firmly so paint cannot bleed underneath. Use quality painter’s tape (not standard masking tape, which bleeds and leaves residue).
Lay drop sheets or plastic sheeting over floors, furniture that cannot be moved, and any surfaces below the painting area. Paint drips and roller splatter are inevitable, and cleaning paint off floors and furniture is far more difficult than laying protection beforehand.
For broader guidance on protecting the rest of the house during a painting project, read preparing your house for painting.
Step 7: Prime Before Painting
Primer is the bridge between the prepared wall surface and the topcoat. It serves multiple critical functions.
Primer seals porous surfaces (new plaster, bare timber, filler patches) so the topcoat does not sink unevenly into the wall, creating dull spots called “flashing.” It provides a uniform base colour and sheen level so the topcoat dries consistently across the entire wall. It improves adhesion between the wall surface and the topcoat, ensuring the paint bonds firmly rather than sitting loosely on top. It blocks stains (water marks, smoke damage, tannin bleed from timber) from bleeding through the topcoat.
When to use primer:
Always prime over bare plaster, bare timber, new filler patches, repaired areas, surfaces where old paint has been stripped, and when changing from a dark colour to a significantly lighter colour. If you are repainting over a sound, well-adhered existing paint in a similar colour, a dedicated primer may not be needed, but a light scuff sand is still essential for adhesion.
For interior painting projects, a quality water-based primer-sealer works for most situations. For stain blocking (water marks, smoke), use a dedicated stain-blocking primer. For exterior walls, use an exterior-grade primer matched to the surface type. The exterior house painting Sydney guide covers exterior-specific primer requirements.
Common Preparation Mistakes
Avoiding these mistakes prevents the most common causes of paint failure. Rushing the drying time between filling and sanding results in filler pulling out of the repair during sanding, leaving the hole partially unfilled. Waiting until the filler is fully cured before sanding ensures a clean, level result.
Skipping the scuff sand on existing paint means the new coat has nothing to grip. It may look fine initially but will peel or flake within months, especially in high-humidity areas like bathrooms and laundries.
Not priming bare patches creates visible dull spots (flashing) where the topcoat has been absorbed unevenly. These spots are most visible in raking light and cannot be fixed by adding more topcoats. The only fix is to prime and start again.
Using the wrong filler for the damage type leads to cracking and re-opening of repairs. Rigid fillers in flexible areas (such as along expansion joints or timber-to-plaster transitions) will crack as the building moves.
