Wood is naturally a porous material so it is important that the surface is sealed to ensure that solvents within subsequent coats are not absorbed too readily which will cause premature drying and potential failure of subsequent paint layers. A first coat of primer will also consolidate loose fibres on the wood’s surface which will enable sanding to a smooth finish before applying finishing coats.
There are a range of wood primers available, all with different qualities, and the choice can be confusing.
Water Based Wood Primers
Water based primers are often acrylic based, are more pleasant to use than solvent based alternatives and can perform well if used correctly. The advantages of water based primers are quick drying, good opacity (covering power), low VOC content and brushes can be cleaned with water.
Water based paints can not be used where the risk of rain is imminent and another disadvantage is that these kinds of paint can clog up abrasive paper which makes it difficult to get a really smooth finish. Some water-borne stains can also bleed through the surface of acrylic paints.
Quick Drying Primer/Undercoat is a general purpose acrylic wood primer and combined undercoat suitable for interior use in a range surfaces including softwoods, hardwoods and building boards including plywood.
MDF Primer is an acrylic primer formulated for use on MDF which is typically more porous than regular softwood. It is quick drying and can be used as an undercoat.
Rubol Primer Plus is a premium quality acrylic primer/undercoat for use on exterior timber. You can use regular water based primer outdoors but it’s worth spending a little extra to get the best result.
Oil Based Wood Primers
Solvent or alkyd based primers (commonly known as oil based primers) have been used traditionally to prime new wood. The advantages are that they dry to a hard finish that can be rubbed down to provide a smooth surface.
Oil based primers are compatible with traditional undercoat and gloss paint and will contribute to achieving a high sheen finish. The disadvantages are slow drying times and they can be messy and unpleasant to use.
Aluminium wood primer is an oil based primer with a high aluminium pigment content. Used for some hard woods which contain high amounts of resin which discolors traditional wood primer. Can also be used for very knotty timber where the use of patent knotting isn’t practical.
One problem with aluminium wood primer is that the bulk of the pigment will settle in the bottom of the can if left for even moderate periods of time so it’s essential that it is thoroughly stirred before use.
There are some other kinds of specialised wood primers but this covers the basics. The general rule with all types of primer is that thorough preparation will always yield good results and when selecting a primer for the job you should always use the best quality primer you can afford.