Preparing a surface for paint: what the labels mean

Look at the surface before the colour chart

Paint can change the appearance of a room, but it cannot make every underlying problem disappear. Loose coatings, damp, greasy deposits and damaged surfaces each need a suitable response. Start by identifying what you are painting and whether the existing surface is sound.

If there is an unresolved cause behind staining, peeling or deterioration, covering it may only hide the evidence for a while. Work out what needs repair or professional assessment before choosing products to improve the appearance.

Cleaning is part of preparation

Surface preparation can include cleaning as well as repairs and abrasion. A degreaser is intended to remove oil and grease, but it still has to be suitable for the material and used according to its instructions. More aggressive cleaning is not automatically more effective.

Read the paint system’s preparation advice alongside the cleaning product’s directions. Surfaces may need residues removed and time to dry before further treatment. Do not mix cleaning products or invent a stronger recipe to speed things up.

Filler, sanding and a suitable key

Filler repairs small holes or uneven areas; wood filler is formulated for suitable timber repairs. Check the material, repair size and intended use rather than assuming one tub fits every defect. A cosmetic filler does not establish that a structural crack has been repaired.

A keyed surface has been prepared to help the next coating adhere. That might involve a specified treatment or suitable abrasion, depending on the surface and product. It does not mean every wall should be sanded as hard as possible.

Before abrading older paint or unfamiliar materials, check what they may contain. Lead paint and asbestos-containing products need appropriate assessment before disturbance. Do not sand a suspect coating simply to see what is underneath.

Primer, sealer and undercoat are different jobs

A paint primer helps prepare the substrate for subsequent coatings. A primer sealer is designed to seal a suitable porous or problematic surface. An undercoat helps provide an appropriate base and appearance before the finishing paint. A product can combine roles, but only within its stated uses.

These names are useful clues, not a universal recipe. Check the proposed products as a compatible system for the exact surface. Do not add extra layers just because several tins are available, or skip a specified preparation coat because the finish paint looks thick.

• Identify the substrate and any existing coating.
• Read compatibility and preparation instructions for the chosen system.
• Check whether the product is intended for interior or exterior use.

Allow for the time between stages

Recoat time is the period recommended before applying another coat. It should not be confused with a promise that the finish has reached its full durability. Conditions and product instructions matter; a surface feeling dry does not settle every question about what comes next.

New plaster has its own requirements. A mist coat is an initial coat of suitably diluted paint used on new, fully dry plaster where the manufacturer specifies it. There is no dilution ratio or waiting period that can be safely assumed for every plaster and paint combination.

Buy a preparation plan, not a pile of tins

Make a short list of the surface, its condition, the chosen finish and the preparation products that system actually requires. Include suitable tools, protection and ventilation arrangements in the plan. This makes it easier to ask a supplier a specific question when a label is unclear.

A low-VOC description does not remove the need to follow handling and ventilation advice. Keep product instructions available, and get competent help where the condition of the building or the material is uncertain.

The takeaway

• Preparation depends on the substrate, its condition and the chosen paint system.
• Primer, sealer and undercoat have different roles; follow compatibility instructions.
• Identify hazardous old finishes and allow the specified drying and recoat times.