BeginnerAbout 30 min
When you need primers, sealers, stain blockers and undercoats, and how to avoid compatibility problems.
What you'll achieve
Choose the right first coats for each surface so the topcoat sticks and looks even.
Suitable surfaces and conditions
Bare wood, MDF, new plaster, bare metal, stains, glossy existing paint, strong colour changes.
Tools and materials
- Correct primer/undercoat for the surface (check data sheet)
- Brushes and roller
- Abrasive paper for denibbing
Safety precautions
- Ventilate the room while painting and drying.
- Wear eye protection when working overhead or with chemicals.
- Keep paint, solvents and tools out of reach of children and pets.
- Read the safety data sheet for solvent-based and specialist primers.
Step by step
- List each surface and its condition from your Lesson 1 plan.
- Bare softwood: seal knots with knotting solution if recommended, then apply a wood primer.
- MDF: use a primer suitable for MDF; edges are very absorbent and may need extra attention.
- New plaster: once fully dry, apply a mist coat or the paint maker's recommended plaster primer — some emulsions should be thinned for this and some must not be; follow the data sheet.
- Bare metal: remove rust and use a metal primer suited to that metal (Lesson 9).
- Stains (water, smoke, marker): apply a stain-blocking primer and let it dry fully.
- Glossy existing paint: clean and sand to a key, then use an adhesion primer if the topcoat maker requires it.
- Large colour change or dark to light: use an undercoat or the recommended number of topcoats.
- Allow each coat to dry as the data sheet says, lightly sand any nibs, dust off, then apply the next coat.
Common mistakes and how to avoid them
- Skipping primer on bare surfaces — uneven sheen and poor adhesion.
- Water-based over unprepared gloss — peeling.
- Mixing brands whose data sheets don't confirm compatibility.
Troubleshooting
- Patchy 'flashing' on walls: filler or bare areas weren't primed — spot-prime and recoat.
- Stain coming back through: it needs a proper stain blocker, not more emulsion.
Final quality check
- Every bare area primed
- Stains fully blocked
- Surface lightly sanded and dust-free before topcoat
Drying and recoating
Drying, recoating and curing times depend on the product, temperature, humidity and ventilation. Use the times on the product data sheet; cooler or damper conditions usually mean longer waits. A coat can feel dry well before it is ready for another coat or for use.
Always follow the manufacturer's instructions and technical data sheet — they take precedence over general guidance here. This is educational guidance only, not a qualification or certificate.