- Bare wood (interior): Use a suitable wood primer/undercoat for good adhesion and an even finish.
- Previously painted wood: Clean/degrease, key the surface, then use a bonding primer/undercoat if needed.
- Knots / resin / tannins: Use a stain-blocking primer to prevent bleed-through.
- Interior vs exterior: Exterior wood needs a primer that supports weather resistance and long-term durability.
- Water-based vs oil-based: Water-based is often quicker-drying/low odor; oil-based can offer stronger sealing on some timber and stains.
When you think of primer, the first thing that comes to mind is probably not a home. But what many people don’t know is that primer can be an essential part of any home renovation. Primer for wood, walls and ceilings can help prep your surface for the best finish possible.
These products are available in both latex and oil-based formulas and can be used on all three surfaces in your home. Primers ensure that the new paint or stain you plan to apply will look good and last longer than it would without primer as a base coat. The type of primer you use depends on the surface you’re working with, as well as your personal preference regarding the smell and ease of application.
An undercoat acts as a base layer for your surface ready for its finish coat. So it will provide neutral canvas in terms of color or providing a smooth base, covering minor inconsistencies. Primers on the other hand can act as:
- a binding medium for subsequent coatings
- a corrosion preventer or rust inhibitor in ferrous metals
- a seal on porous surfaces
- a protection for surfaces prior to painting
- an adhesive mechanism to allow top coats to adhere to non-porous (shiny etc) surfaces
- a barrier between the surface and finish coat, for example were surface is heated (such as hot water pipes)
- a seal for surfaces (especially in wood) to cover stains and prevent bleed-through of subsequent top coats
- a barrier where a surface has chemical properties (such as high alkaline content) which might react and affect application of the top coat
Which Primer or Undercoat do I Need?
- Your surface – what it’s made of
- Whether it has been painted or treated previously
- The quality of the surface
- What you hope to apply as a finish coat
Wood Primers
Wood almost always needs a primer unless the surface is in good condition and has been previously painted. In this case you can usually get away with a light sanding and then overpainting with a similar finish coating. Bare or new wood (that hasn’t previously been painted) is highly porous, so a primer is necessary to seal it before applying paint. A primer will also prevent moisture from getting into the wood and will mask any knots. Tannins present in new wood can seep through paint, as can stains in previously painted wood, so again, primer helps to avoid this. The type of wood you’re planning on painting may absorb a primer in different ways as hardwoods and softwoods have different properties. In terms of primer, treat surfaces like chipboard in the same way you’d treat softwood.
How to Apply Wood Primer to Bare or New Wood
Although it might look smooth, always sand new or bare wood before priming. Follow the direction of the wood grain, if you sand across the grain you risk damaging the fibres of the wood and your surfaces will not be smooth. If there are obvious knots, seal them with a knotting solution or an aluminium primer depending on the type of wood.
Paint doesn’t soak into knots in the same way as the rest of the wood. Knots can also leak sap which may penetrate subsequent paint coatings and look unsightly.
Apply your wood primer (or dual purpose primer/undercoat) with a brush or roller in smooth strokes and allow to dry before sanding then apply further coat if needed.
Once dry, apply undercoat or your top coat if you’ve used a dual undercoat/primer.