Primer Paint: Everything You Need to Know

Whether painting a brick wall or a wooden chair, primer is essential for creating a smooth and adhesive surface for a topcoat. Primer paint will adhere to a variety of materials, ensuring the long-term stability of your painted surface. In this guide from Building Materials Nationwide, we’ll explore the different types of primer paint sold in the UK, and look at what types of primer are the best for various types of materials.

What is Primer Painting?

When painting any surface, an undercoat of primer paint helps to create a consistent and durable base. Primer paint is applied much like traditional paints, creating an even coverage over a variety of materials. It is designed with adhesion in mind and will come in a neutral colour, typically white, that won’t interfere with the colour of the topcoat.

In addition to adhesion, primer paint will obscure imperfections on a surface, such as different coloured bricks on a wall, or non-original elements within a piece of furniture. It will also cover stains, meaning they won't be visible through the finished paint. By adhering to the surface and creating a smooth base, the paint will attach to the wall better and fewer coats will be required. If you are looking to paint over an existing coloured surface, a primer will help neutralise the underlying colour.

Is a Primer Undercoat Before Painting Essential?

Primer brings a range of benefits when painting and paint manufacturers will argue that it is essential in all cases, helping their paint to look its best and offering great long-term performance. 

Some DIYers however would argue that it is not essential in every instance, adding time and cost to an ongoing job. There are also self-priming paints that claim to offer broadly comparable benefits to using a standalone primer. 

Here are some situations where using a primer would be considered essential:

• Poor condition surfaces: Whether it’s a crumbling and uneven wall or an older piece of furniture, surfaces that are in some way damaged or uneven can benefit from an undercoat of primer to ensure the paint fully adheres.
• Masking imperfections: If a wall has issues with staining or discolouration, opting for a base coat of primer can help obscure this within a finished wall.
• Changes in hue or sheen: When painting over existing paint, choosing a radically different hue or sheen can cause issues with colours crossing through to the new topcoat. Whether moving from white to black or from gloss to eggshell, using a base layer of primer paint will ensure that only the topcoat is visible.
• Painting an absorbent surface: Whether painting a bare masonry wall or an unvarnished wooden panel, absorbent surfaces can make it difficult to apply paint, requiring extra coats to avoid a patchy finish. Primer paint will cover an absorbent surface, creating a secure base upon which paint can be applied.
• Painting a humid area: In bathrooms, kitchens, and areas with high humidity, using an undercoat of primer can provide further protection against dampness and mould. 

If you are painting a bare, flat surface, or covering one paint colour with another similar colour, then you may not need to use primer.

What Types of Primer Paint Are Sold?

When shopping for primer paint you’ll have several options, which bring specific benefits and drawbacks for certain projects and topcoat paints.

Oil-Based Primer

Oil-based primers can be used on a variety of surfaces, and perform well with oil-based or emulsion topcoats. An oil-based primer will cover stains well and handle temperature fluctuations with ease. It will be commonly used on wood and metal, bringing benefits to any surface that will be touched like doors and cabinets, though it can also be used on plasterboards. 

Oil-based primers should not be used on bare masonry. Drawbacks to keep in mind include the complex application, as it requires mineral spirits for thinning and cleanup, unlike some other options. There will also be a 24-hour drying process for oil-based primers, during this time it will release high levels of VOCs (volatile organic compounds) that may pose health risks.

Water-Based Primer

Water-based primers are effective on masonry, concrete, wood, metal, and plasterboarding. They dry quickly, with a 3 to 4-hour window making them much faster to apply than oil-based varieties. 

In addition, water-based primers are easier to apply and clean, are less brittle, and will not emit any VOCs. The drawback of water-based primers is that they are less effective at covering stains than oil-based options. Water-based primers are sometimes sold as acrylic primers, which can contain organic solvents to improve adhesion.

Shellac Primer

Another option is shellac primer, which is a solvent-based primer that can be used on wood, metal, plastic, and plaster, offering excellent stain blocking. They dry in under 1 hour and can be used with oil-based and emulsion paints. Shellac primers will need to be mixed with denatured alcohol before use, and like oil-based primers, they will emit dangerous VOCs.

Self-Priming Paints

Self-priming paints are thicker and designed to offer both the benefits of primer and the colour of topcoat paint. While some DIYers will be satisfied with the results, particularly on walls or surfaces in a reasonable condition, professionals would typically avoid this option. Especially when trying to paint an absorbent or uneven surface, the base coat of primer has a different function from the topcoat, and combining them can offer an inferior version of both.

The Best Primer Paint For Different Materials

Whether looking to paint wood, masonry walls, or plasterboarding, the best primer option can differ. 

Priming Paint For Wood

While oil-based primers would be the more common choice for wood, water-based options will also work well. If priming a wood that is damaged or weathered, you should sand down and remove as much of its imperfections as you can. Specific wood primers are sold, which will be designed to create a smooth and adhesive surface on wood, be that a door, a chest of drawers or a shed. Another point to keep in mind is that redwood timber, like Douglas fir and cedar, should be primed with an oil-based option. This is because the red from the wood can sometimes bleed through a water-based primer and affect the surface colour.

Priming MDF

Using a solvent-based primer like shellac on your MDF can create a uniform surface. Water-based primers may cause the disconnected fibres of MDF to swell, giving an uneven final appearance.

Metal Primer

Regular paint will struggle to bond with the surface of a metal, making priming an important step. An oil-based primer would be the most common choice, offering an adhesive and strong base. If you are using emulsion paint as a topcoat, it’s essential to use an oil-based primer as the water within the emulsion can cause rusting if applied directly to metal. There are several specific metal priming paints available, designed for different metals, conditions of metal, and surrounding environments.

Primer Painting on Masonry Walls

Using primer paint for an undercoat on bricks is a necessity, with the uneven and porous surface of bricks absorbing much of any topcoat paint applied to them. There are specialist primers available for masonry surfaces, typically water-based, alongside primers specifically for exterior masonry.

Priming Plaster Walls

Water-based primers would typically be used over a plaster wall. It’s important to let a freshly plastered wall dry for around a week before painting. An alternative to primers for plastered walls is to create a mist coat, which is a mixture of three parts emulation and one part water, intended to allow some of the coat to absorb into the plaster wall, creating a surface that the topcoat can adhere to more easily.

Priming Plasterboards

Provided the joins between boards have been sealed you can paint directly onto plasterboards. Like a plastered wall, you can apply a mist coat of emulsion as an alternative to primer. A water-based primer would otherwise be the standard choice.

How is Primer Applied?

Primer is applied in the same way as topcoat paints, with paint rollers giving the quickest application. Spray primers are also available, which can apply a better coating on complex shapes such as metal elements. You’ll need to ensure that the walls are clean and free of debris beforehand. Priming coats should be fully dried before topcoats are added.

Building Supplies Delivered Across the UK

Building Materials Nationwide works with professionals across the UK, providing them with a comprehensive range of building supplies, delivered at a competitive price. Through our website, we offer trade accounts, through which you’ll gain access to the services of a dedicated account manager. 

Our dedicated account managers are there for you, helping you to source whatever supplies you need through our massive network of suppliers. Whether looking for primer paint, topcoat paint, or specialist paints for wood, metal, or exterior use, your dedicated account manager will be able to get it delivered to you at great trade prices. Sign up for a trade account through our website today, or tell us what you need through the form below to get started.