Painting wood: answering five important questions about paint choice

Wood surfaces come in all shapes and sizes. The way you paint wood depends a lot on what type of wood it is, whether it is located indoors or outdoors and its condition. We answer five important questions about painting wood.

Wood has some specific properties that determine how well paint will adhere to it, how durable the finish will be and how much paint you need to ensure good coverage. Those properties are porosity, dimensional stability, hardness, texture and tannin or oil content. They differ depending on the type of wood.

• Porosity is the degree to which wood has small openings or pores. Porous wood (such as oak and meranti) absorbs more paint, so a good primer and/or several topcoats are needed for good results. With less porous woods (such as mahogany), one coat may suffice, but we still always recommend applying two finishing coats. 

   

• Dimensional stability is the degree to which wood shrinks or expands under the influence of moisture and temperature fluctuations. Structures of non-dimensionally stable wood require flexible paint to prevent cracking. 

   

• Hardness is the degree to which wood resists denting or scratching. Soft woods (such as pine and spruce) require a more flexible paint or a thicker primer to keep the paint layer durable. Hard woods (such as teak and walnut) need less protection against damage. 

   

• Texture is the visible and tangible structure of the wood surface. Wood species with coarse textures (such as oak and Douglas fir) require thicker paint or several coats. Smooth wood (such as birch and poplar) requires less paint but good adhesion. 

   

• Tannin or oil content is the amount of natural chemicals found in the wood. Tannin-rich woods (such as oak) can bleed through the paint and thus require an insulating primer. Oily wood (such as teak) requires a special adhesive primer to ensure good paint adhesion.

That varies from wood species to wood species. This is because some wood species are more water-resistant than others. Wood species with a high tannin or oil content, such as oak, are not suitable for water-based paint because the tannins and oils will enter into a chemical reaction with the water. The tannins or oils will bleed through the paint, leaving stains or discolouration. 

For wood types where water-based paint should not be applied directly, you should either use a solvent-based alternative or apply an insulating primer first. In most cases, a primer is the best solution as it also provides certain protections. Below is a list of most common types of wood and whether they are suitable for water-based paint or not.

A film-forming paint is a paint that, once applied, forms an impermeable layer or ‘film’ on the surface of the material to which it is applied. This film protects the underlying material from external influences. In general, most types of wood require a film-forming paint, but again there are factors that influence the choice of a film-forming or non-film-forming paint. 

The most important factor is whether the wood is located outdoors or indoors. Wood outdoors is subject to moisture and temperature fluctuations that will cause it to shrink and expand depending on its dimensional stability. If you apply a hard film-forming paint to 
non-dimensionally stable wooden structures (e.g. a garden shed made of softwood), cracks will soon appear in the paint layer.

Absolutely! Interior wood is exposed to very different conditions than exterior wood. Indoor wood faces relatively stable temperatures and humidity, while outdoor wood is constantly affected by the weather. Think UV radiation, rain, wind and large temperature differences. Indoor or outdoor wood painting therefore requires a different approach and, above all, the right products. The elasticity of your paint is even more crucial than for other substrates.

Oak interior doors, pine garden fences, a teak terrace ... It can seem difficult to choose the right paint. Fortunately, Zinsser makes it easy for you: our products are suitable for most types of wood, you just need to take into account whether you are painting indoors or outdoors.

• Painting wood indoors 

  B-I-N Aqua is the best Zinsser primer for treating soft wood indoors. It is ideal for porous woods indoors and blocks stains from tannin, knots and resin. For hard woods, we recommend B-I-N. And PermaWhite, our mildew-resistant primer and topcoat in one, gives you a durable, washable, moisture-resistant and scratch-resistant finish. Follow these steps to paint wood indoors.  

• Painting wood outdoors

  The best water-based Zinsser product for painting exterior wood is Zinsser Allcoat Exterior. This primer and topcoat in one has a better elasticity than conventional varnishes or other moisture-regulating primers and will therefore not crack when the wood shrinks or expands. Follow these steps to paint wood outdoors.