Why surface preparation before painting matters

When a paint job is done and dusted, it’s often not the paint itself that lets the finish down: it’s the surface underneath, from cracks and movement gaps to stains and uneven porosity.

These surface problems can lead to peeling, cracking and other visible defects, along with unhappy clients and costly callbacks – even when the paint has been applied correctly.

The good news? Surface preparation before painting, including cleaning, repairing, filling, sealing and priming a substrate so paint can adhere properly, will deliver a durable, even finish and help prevent defects and callbacks.

Key overview: Why is surface preparation important before painting?

Preparing the surface before painting is the foundation of a high-quality and long-lasting paint finish. Some of the reasons to undertake proper preparation before a job include:

• To ensure the final paint result is of a high standard: Common surface issues, including movement cracks, flaking surfaces, hidden water damage and surface contamination, should be repaired and prepared properly before you begin painting;
• Ensures a high-quality and lasting finish: Proper paint adhesion is essential, while paint preparation also hides imperfections, and prevents future peeling or blistering. This critical step creates a uniform base and avoids costly touch-ups or premature repainting; and
• Fewer callbacks: Better preparation and choosing the right repair products from the start can lead to a better end result and reduce the risk of callbacks.

Tip: Always wear the appropriate safety equipment (safety glasses, gloves and a mask, for example) when required on the job. Always follow the instructions for the product or equipment.

What causes paint failure on walls and plaster?

Paint only performs as well as the surface underneath, with many paint failures coming down to poor paint preparation, and inadequate wall and plaster repairs.

Common surface issues include:

• Movement cracks that reopen over time;
• Gaps that allow moisture ingress;
• Patched holes that show through paint;
• Flaking surfaces; and
• Uneven porosity that can cause flashing and uneven sheen.

Hidden water damage and mould can also affect paint performance, often only becoming apparent when the surface is prepared or coated. Untreated movement cracks can contribute to moisture damage, as they allow moisture to enter over time.

Dust, grease and other types of surface contamination can prevent fillers and sealants from bonding properly and cause paint adhesion failure.

These problems aren’t always obvious at handover. Unfortunately, they tend to become more visible over time, well after the job is done.

How to properly prepare a surface before painting?

While paint finish quality can be traced back to poor surface preparation, each issue doesn’t necessarily require the same approach to repair.

Using the right products for wall and plaster repair is essential when it comes to paint preparation before commencing any work. For instance, a rigid filler on a movement joint may look fine at handover, but once the joint moves, a crack can reappear through the paint.

“A common mistake is repairing a gap without first identifying why it has formed. If a joint is expected to move, it's important to use a highly elastic, paintable sealant that can accommodate that movement,” Scott Robinson, Head of Technical Services & Training at Selleys, says.

“Choosing the right repair product for the application helps reduce visible defects, improve durability and minimise costly callbacks.”

Here’s a rundown of some paint preparation products and what they should be used for:

• Stain blockers are designed to stop bleed-through;
• Joint compound is used for plasterboard joins;
• Patching compounds are better suited to repairing holes and other static damage; and
• Primer sealer undercoat creates an even surface for porous repairs, new plaster, timber and previously stained surfaces, reducing flashing and uneven sheen.

What painting mistakes lead to rework and callbacks?

• Ensure the right paint preparation and paint for the environment: The environment you’re working in is an important consideration, with outdoor jobs requiring products that can withstand moisture and UV exposure.
• Leave enough time between painting preparation and painting: Painting over a gap filler or sealant that hasn't been cured properly can lead to defects like mud cracking and crazing.

How can painters improve paint finish quality?

Paint prep might require a bit more time, effort and planning, but in the long run, it can lead to a more consistent result – one that’s higher quality and more durable, with fewer snags.

Taking the time to do paint preparation before painting will:

• Ensure the surface is clean, treated and primed before a lick of paint hits the surface, helping support paint longevity;
• Remove contaminants, imperfections and previous coatings that can affect adhesion and durability of the new paint finish;
• Support a smoother handover at the end of the job; and
• Help minimise callbacks, which can be costly and time-consuming, while also affecting client satisfaction and a tradie’s reputation for quality workmanship.

Diagnosing the cause and choosing the right repair product from the start can mean fewer defects, fewer callbacks and a finish that’s built to last.

Frequently Asked Questions: Paint preparation

How can you tell if a crack is cosmetic or a sign of a bigger problem?

Hairline cracks are often cosmetic, but persistent, recurring, widening or stepped cracks can indicate movement or structural issues. If the cause isn’t clear, investigate before repairing and painting.

When is it better to repair than replace damaged plasterboard?

Small holes and minor damage can usually be repaired, but plasterboard that’s severely weakened or has water or mould damage is often better replaced.

What causes repaired areas to flash after painting?

Flashing after painting can be caused by uneven porosity between the plaster repair and surrounding surface, skipping or using the wrong primer, or differences in texture or absorption becoming visible only after painting.

How can painters reduce snag items at handover?

Always perform a thorough inspection of the substrate before painting, then use the correct repair products and allow them proper time to cure.

What should painters look for before applying the first coat?

A thorough surface inspection should involve checking for cracks, movement gaps, holes, flaking paint, mould or moisture, stains, and identifying any areas that require cleaning, repair, priming or stain blocking before painting.

What about flooring preparation?

Like painting, it’s about what lies under the surface of a flooring job – get fewer callbacks with this expert flooring prep guide.