How to Prepare Walls Before Painting

Preparation determines whether paint looks smooth and remains attached. The correct process depends on the existing coating and the cause of each defect, so inspect before filling everything in sight.

Check the surface condition

Look for loose paint, powdery areas, cracks, water marks, grease, mould, raised filler and movement around joints. Press suspect areas gently rather than coating over them. A stain with an active leak behind it must be solved before decoration.

Older buildings can contain lead paint or other hazardous materials. Avoid uncontrolled dry sanding or heat until the risk has been assessed. Current HSE guidance explains controls for work that may disturb lead-containing coatings.

Clean before repairing

Dust, cobwebs and general dirt reduce adhesion. Kitchens, fireplaces and high-touch areas may need a suitable degreaser. Rinse where the product requires it and allow the wall to dry.

Do not soak plaster or use a strong chemical without checking that it is compatible. Mould and damp need their cause addressed rather than being hidden by paint.

Remove loose material

Scrape only what is unsound and feather the edge of remaining firm paint. Deep cracks, repeated movement and blown plaster may need more than ordinary surface filler. If a repair continues opening, identify the reason before repeating it.

Fill in controlled layers

Use a filler suitable for the substrate and depth. Apply deep repairs in the way the manufacturer specifies instead of bridging a large void with one surface layer. Slightly proud, controlled filling is normally easier to sand than a wide mound.

Allow repairs to dry completely. Drying time changes with depth, temperature and ventilation, so colour alone is not always a reliable guide.

Sand and control dust

Sand enough to remove ridges and blend the edge without unnecessarily damaging the surrounding surface. Use extraction or another appropriate dust-control method, ventilate and wear suitable protective equipment for the task.

Vacuum and wipe dust away before coating. Paint applied over fine sanding dust can have poor adhesion even when the wall looks clean from a distance.

Prime problem areas

Bare plaster, filler, stains, glossy surfaces and porous patches may need different primers. Choose a system described as compatible with both the substrate and finish coat. A random coat of leftover paint is not a substitute for checking the specification.

Inspect under useful light

Use side lighting to reveal ridges and pinholes, but judge the final finish in normal room lighting too. Confirm walls are dry, stable and dust-free before the first full coat.

When preparation becomes specialist work

Extensive coating failure, suspected lead, ongoing damp, structural movement or major plaster repairs need the right diagnosis. JP Whyte Decorators can assess ordinary preparation as part of an interior decorating quote and identify when another specialist trade should be involved.

Inspect in good light

Look along the wall rather than only straight at it. Side light shows dents, ridges, old drips and poor previous repairs. Mark defects lightly, then decide whether each area needs cleaning, filling, sanding, sealing or specialist investigation. Active damp and movement cracks should not be hidden under filler.

Work in the right order

• Protect floors, fittings and nearby furniture
• Remove loose material and deal with the cause
• Clean dirt, grease and residue with a suitable method
• Fill only sound, dry areas and allow the filler to cure
• Sand safely and remove dust
• Prime bare or problem surfaces where required

Test the existing coating

A new coat needs a stable base. If old paint is powdery, peeling or poorly bonded, painting over it transfers the weakness to the new finish. Test a small area and follow the primer or top-coat data sheet. Newly plastered walls need the coating system specified for fresh plaster; do not guess the dilution.

Keep dust under control

Use suitable respiratory and eye protection, ventilate the room and connect extraction where the tool allows. Older coatings may require extra precautions. When the wall is ready, it should be clean, dry, stable and uniformly prepared—not merely smooth in the most visible patch.