Metal
Bare, previously painted or lightly corroded steel.
Preparation & Spraying
How to Prepare a Surface Before Applying Aerosol Paint
Good preparation is the key to a smooth, durable finish. Follow these practical steps to make sure the surface is clean, sound and ready for primer and paint.
The foundation of a lasting finish
Why surface preparation matters
Even the best coating can fail when it is applied over dirt, grease, rust, loose paint or an unsuitable existing finish. Correct preparation improves adhesion, reduces the risk of peeling and corrosion, and helps the final coats look smoother and last longer.
The aim is not simply to make the surface look clean. It must be sound, uniformly keyed, free from contamination and compatible with the primer and topcoat you plan to use.
Suitable substrates
This guide applies to
The exact preparation and primer will depend on the material and the condition of the existing finish.
Aluminium
Bare or previously painted aluminium.
Plastic and uPVC
Suitable rigid plastics, flexible plastics and uPVC.
Wood and MDF
Bare, sealed or previously painted timber products.
Powder coat
Sound powder-coated metal and aluminium surfaces.
Mixed substrates
Projects containing more than one material or coating type.
Preparation essentials
What you will need
Use clean, suitable materials. Contaminated cloths, worn abrasives and poor masking can spoil an otherwise good job.
Abrasives
Abrasive paper, sanding sponges or a suitable wire brush.
Degreaser
A compatible panel wipe or surface degreaser.
Clean cloths
Fresh lint-free cloths and a tack cloth where appropriate.
Masking materials
Quality masking tape, paper and protective sheeting.
Correct primer
A primer chosen for the substrate and topcoat system.
PPE
Gloves, eye protection and suitable respiratory protection.
Step-by-step
Surface preparation process
Work methodically. Do not move to the next stage until the surface is sound, clean and ready.
Inspect and identify the surface
Confirm what the item is made from and whether it is bare, previously painted, powder coated, galvanised or plastic. Look for rust, blistering, cracks, silicone, wax, grease and previous repairs.
If the existing coating is unknown, test a hidden area before applying a complete system.
Remove fittings and protect the work area
Remove handles, seals, trims and other fittings where practical. Protect floors, walls and nearby objects from dust, cleaner and overspray.
Remove rust and loose coating
Remove all loose rust, flaking paint, blistered coating and failed filler. Use an appropriate abrasive, scraper, wire brush or mechanical method without damaging the sound substrate.
Repair damage and feather the edges
Repair chips, dents, cracks or deep scratches with a compatible repair product. Sand the repair level and feather the surrounding paint edges so no hard ridge remains.
Sand and key the full surface
Abrade the complete area evenly so the primer or topcoat can adhere. Use a grade suited to the material and coating system, refining coarse scratches before painting.
Avoid sanding through sound coatings unless the substrate needs to be exposed.
Clean and degrease thoroughly
Remove sanding dust, grease, oil, wax, polish and silicone using a compatible degreaser and clean lint-free cloths. Change cloths frequently rather than spreading contamination around.
Allow the surface to dry fully and avoid touching it with bare hands afterwards.
Mask the surrounding areas
Use quality masking tape and paper to protect everything that must not be painted. Press tape edges down firmly and avoid placing tape where it will leave a hard paint edge in a visible area.
Apply the correct primer
Prime exposed substrate, repaired areas and any surface that requires additional adhesion or corrosion protection. Apply the primer exactly as stated on its label and Technical Data Sheet.
Allow it to dry, then refine it if required before applying the colour coat.
Primer selection
Choose a primer for the substrate
Primer is not one universal product. It should be compatible with both the substrate and the topcoat system you intend to use.
Bare or rusted steelUse a compatible anti-corrosive metal primer after all loose corrosion has been removed.
Aluminium or galvanised metalUse the adhesion or etch primer specified for the coating system and substrate.
Plastic or uPVCUse a compatible plastic or adhesion primer where the paint system requires one. Confirm the plastic type first.
Wood or MDFUse a compatible sealing or high-build primer, paying particular attention to porous edges and repaired areas.
Sound existing paint or powder coatThoroughly key and clean the coating. Use an adhesion primer if required by the chosen topcoat system.
Important: A product described as direct to metal may still benefit from primer on bare, corroded or mixed substrates. Always follow the label and Technical Data Sheet for the complete coating system.
Useful answers
Frequently asked questions
Do I need to remove all the existing paint?
No. Sound, well-adhered paint can normally remain if it is compatible, thoroughly cleaned and properly keyed. Remove all loose, flaking, blistered or poorly adhered material.
What grit abrasive should I use?
The correct grade depends on the substrate, the amount of damage and the coating system. Coarser grades remove rust and defects, while finer grades refine the surface before primer or paint. Always avoid leaving scratches that the next coat cannot fill.
Can I paint directly over rust?
Loose and active corrosion should be removed before painting. Some specialist systems tolerate tightly adhered residual corrosion, but only when their instructions specifically allow it. For a dependable result, prepare the steel and use the recommended anti-corrosive primer.
Do direct-to-metal paints need primer?
Not always, but primer can still improve corrosion protection, adhesion and uniformity, particularly on bare, repaired, rusted or mixed substrates. Follow the exact instructions for the direct-to-metal product you are using.
How do I know the surface is ready to paint?
It should be dry, stable, uniformly keyed and completely free from dust and contamination. There should be no loose coating, active rust, glossy unabraded areas or visible residues from cleaner.
Ready to start your project?
Prepare carefully, use the correct primer and follow the product instructions. A little extra time at this stage can make a major difference to the final result.