Priming a wall: when is it needed and how do you do it?

Short answer: you need to prime a wall if it is highly absorbent or powdery. That almost always applies to new plaster, plasterboard, aerated concrete, bare masonry and filled patches. A well-painted, sealed wall usually does not need a primer. You can test it in a minute with the wet finger test and the rub test. Without priming, the wall absorbs the paint unevenly, you get stains and streaks and you need more coats of paint.

👷 For large areas, high stairwells, damp problems or a facade at height, a painter or plasterer is the best choice. Calling in a professional is never unnecessary: they recognise the cause of damp or peeling and choose the right system.

Does your wall need priming? Two tests

• The wet finger test: wet a sponge or your finger and stroke the wall. If the spot darkens immediately and the water soaks in quickly, the wall is highly absorbent.
• The rub test: rub a dry, dark cloth or your hand over the wall. If white powder comes off, the wall is powdery.

If the wall is highly absorbent, use a primer. If it is powdery, you need a stabilising primer that binds the loose particles. If in doubt, prime: an overly absorbent wall causes more problems than an extra coat.

Which walls need it?

• New plaster: let it dry completely first. Read about repairs in our blog on repairing plaster.
• Plasterboard with filled joints: without priming the joints show through.
• Aerated concrete, sand-lime brick and bare masonry: these are very absorbent.
• Patches that have been filled: priming locally prevents dull spots.
• Old, powdery wall paint: stabilise first.
• Facades: use a primer that matches the facade paint, such as Kerakover Acrilex Primer for facades or Kerakover Silox Primer for facades.

Which product do you choose?

For interior walls a water-based universal wall primer is a good choice. On highly absorbent or sandy surfaces a deep-penetrating primer penetrates deeply and strengthens the surface. If mortar or plaster will be applied to the wall later, use a bonding primer for mortar and plaster for better adhesion. Always read the technical data sheet: it states the consumption per m², the dilution and the drying time.

How to prime a wall in five steps

1. Protect the room. Lay masking film on the floor and mask frames and skirting boards with blue painter's tape. Read more in our blog on masking tape and protective film.
2. Clean and smooth the wall. Scrape off loose material with a putty knife with aluminium blade, fill holes and sand unevenness with a sanding block grit 120. Then dust the wall.
3. Stir the product and pour it into a paint tray or 12-litre bucket. Only dilute if the instructions say so.
4. Apply the product with a velour roller on a telescopic pole from 1.1 to 2 metres for large areas and a acrylic brush for corners and edges. Work wet-on-wet and saturate the surface without puddles or drips. No glossy layer may remain on the wall; that actually causes adhesion problems. Read which roller suits which job in our blog on paint rollers and brushes.
5. Let it dry thoroughly as stated on the packaging and then paint the wall. You will find the step-by-step plan in our blog on painting a wall; for the ceiling read our blog on painting a ceiling.

💡 When priming a ceiling, work from a sturdy wooden painter ladder and start at the window. That way the light shows you straight away where you have already been.

⚠️ If damp patches, mould or peeling layers keep coming back, priming is not the solution. First have the cause of the damp investigated by a professional.

Common mistakes

• Too much product: a glossy film means the paint adheres poorly.
• Painting too early: the product must be completely dry.
• Priming over dust or grease: the product then sticks to the dirt instead of the wall.
• Treating new plaster too early: moisture still in the wall gets trapped.

Working safely

Wear safety goggles when working overhead: drops of primer in your eyes are painful. Use work gloves with nitrile coating to protect your skin and ventilate the room well during and after the work. Only work at height from a sturdy ladder or mobile scaffold, never from a chair or table. Keep children and pets out of the room until the product is dry.

Can I use diluted wall paint as a primer?

On a slightly absorbent wall some paint manufacturers recommend a diluted first coat. On highly absorbent or powdery walls a proper primer or stabilising primer works better.

Do I need to prime before wallpapering?

Yes, on absorbent surfaces. The wallpaper then adheres better and is easier to remove later.

How long does the primer need to dry?

That differs per product, temperature and humidity. Follow the drying time on the packaging.

With two simple tests you know whether your wall needs a primer. That way your paintwork turns out even and fewer coats of paint are needed.

Read also: How to paint a wall · How to paint a ceiling · Repairing plaster: fixing cracks and holes

Where can you find everything for this job?

At Saniso, the online store for DIYers and professionals, you will find tools, materials and personal protective equipment for your job.

• Browse our construction tools and our workwear and safety.
• Create a customer account and order easily.
• Working on a bigger project or want to hand over the job? Request a project quote.
• Book a showroom visit, at least 24 hours in advance.
• Not sure which material suits your job? Get in touch with us.

In doubt about the approach? Feel free to call in a professional.

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