Painting Wood Wool Acoustic Panels: RAL Colours Without Killing the Acoustics

One of the quiet advantages of wood wool cement board, or fibrolite as it is known in much of Europe, is that it takes paint well. The open fibre structure that absorbs sound also holds pigment, so a painted wood wool ceiling keeps its texture and character. The catch: paint applied the wrong way closes the pores that make the panel work acoustically. Here is how to get colour without losing performance.

Start from the factory colour if you can

Sonablock panels come in five standard finishes: Natural, White, Light Grey, Dark Grey and Black, with other RAL tones available on request for volume orders. A factory finish is applied under controlled conditions with the right paint load, so absorption values are preserved and every panel matches. If your project simply needs white, grey or black, order it that way rather than painting on site. It is cheaper than the labour of painting and removes all risk.

When on-site painting makes sense

Repainting is the right tool when an existing wood wool ceiling looks tired, when a brand colour is needed for a fit-out, or when cut edges and fixings should blend in after installation. Wood wool has been overpainted in Northern European schools and halls for decades; panels from the 1970s are still in service under several coats. The material itself does not mind paint. Its acoustics do, eventually.

Spray, do not roller

The rule that matters most: use an airless spray with a light, even pass. A roller pushes paint into the fibre mesh and bridges the gaps between fibres, and those air paths are exactly where sound enters the panel. One rolled coat can visibly fill the surface; two can turn an absorber into a reflector.

• Use a matt, water-based emulsion. Avoid thick elastic or vinyl paints that form a skin.
• Thin the first coat slightly and keep the gun moving; the goal is colour on the fibres, not a film across them.
• Two light spray coats are the practical maximum per repaint if absorption matters in the room.
• Let each coat dry fully. Wood wool holds moisture briefly in its surface fibres, and rushing coats leads to blotching.

How much absorption do you lose?

Industry testing on wood wool products generally shows that one or two properly sprayed coats reduce absorption only marginally, in the order of a few percent, while heavy or rolled application can cut mid and high frequency absorption dramatically. Treat every repaint as spending from a limited budget. A ceiling that has already been painted three or four times over the years should be assessed honestly: if the surface looks clogged and smooth rather than fibrous, replacement panels will restore both looks and acoustics, and at that point a factory-coloured panel is the sensible route.

Painting cut edges and screw heads

Exposed cut edges can be touched up with a small sprayer or even a brush, since edges contribute little to total absorption. The same goes for screw heads. This is the one place where brush application is fine.

A note on fire classification

Sonablock carries a B-s1,d0 reaction to fire classification as delivered. A thin coat of standard emulsion does not normally change how the product behaves in practice, but the tested classification formally applies to the panel as manufactured. For projects where the fire certificate must hold on paper, specify the colour from the factory instead of painting on site. That keeps the documentation clean for the fire engineer.

Explore the standard colours and panel formats in the Sonablock wood wool collection. If you need a specific RAL tone for a larger project, contact us and we will quote a factory finish.