weathered wood

Paint vs Primer – What’s the Difference?

As professional painters, we field a lot of questions about the details of our industry. The most common one might be, “when do you need primer,” and right behind it is the related question, “what’s the difference between paint and primer, anyway?” Laying down a coat of primer beneath your final coat of paint might not seem like a big deal, but it is. A good primer can dramatically improve the look, finish, and longevity of the paint.

To clearly explain the difference between paint and primer, we’ve taken the time here to break down all the differences between the two products. Read on to learn about what separates the two, as well as the benefits and appropriate uses of primer coats. We’re also exploring how primer reacts to different surfaces, and how to use it to get the best results on any painting job.

The key difference that makes primer distinct from finish paint is that its important ingredients are its resins. Primer lacks the pigments that give paint its distinctive colour. Primer is intended to seal and stabilize the surface to be painted. The resins in a primer for wood make the painting surface non-porous and provide a uniform layer that the finish paint can bond with evenly.

The pigments that distinguish finish paint have additional benefits beyond colour. They also make paint long-lasting and washable. White pigments are very important for delivering this durability, even in non-white paint colours. High-quality products typically use titanium dioxide as their primary white pigment; this makes these paints spread farther, last longer, and look better when properly applied. Cheaper paints often make do with ‘filler pigments’ such as talc. The economic trade-off is inevitable; for a lower price tag, you get a less durable product.

As noted above, one of the main jobs of a primer coat is to seal the painting surface. This is particularly important when you’re painting porous surfaces, like wood. A porous surface is bad for a single-coat painting because the pores of the material trap air underneath the paint. That air will try to escape, putting stress on the paint and causing it to crack and peel relatively quickly. A coat of primer stops this problem in its tracks and creates a more appropriate surface for paint application.

Primer is also helpful (and economical!) because it reduces the total amount of paint you need to achieve your desired results. Without primer, you have to apply more paint. Since paint costs more than primer, attempting to save money by skipping the primer will often have the opposite outcome.

Many people believe that all primers or clear or neutral-coloured. Although the lack of pigment does tend to make primers relatively dull, they can also be tinted with basic colours of their own. This can be quite helpful when you are aiming for a strong finish colour or are moving between very dark and light tones. A tinted primer will help you achieve a satisfying, opaque finish coat while once again reducing the total amount of paint you have to apply.

The Main Types Of Primer And Their Ideal Uses

Choosing between the different types of primer often depends more on the other products being applied than on the material being painted. Latex paints, oil based paint, high-intensity colour pigments, and stains all call for a primer product formulated specifically for their needs. Do not get primer mixed up with masonry primer which isn’t recommended for wooden surfaces.

Oil-Based Primers

An oil based primer deliver a very smooth finish and they are extremely durable because the product remains elastic even after it is completely dry. You can use oil primers indoors or outdoors, and their durability makes them particularly suited to application in high-traffic areas (like decks, entryways, or main halls) where painted wood surfaces are likely to take a lot of abuse. Oil primers are also heavier than other products, making them ideal for covering up a surface that is stained or discoloured with products like stain blocking primer.

Oil primers adhere best to bare wood and metal and are less effective on stone. Oil primers also work poorly on galvanized metal; they will begin to flake quickly on such surfaces. A latex-based primer is required for galvanized metal.

Applying an oil-based primer is more time-consuming than using other products. These primers dry slowly, particularly if the air is humid. If you need to apply an oil primer, you should try to do so in the warmest, driest possible weather.

One situation where an oil primer becomes an absolute necessity is when you are applying water-based latex paint to a surface that has old oil-based paint on it. No matter how old oil paint is, it can still release its oils into the newer layer above. In the same way that greasy foods will discolour a paper or cardboard wrapper, oil-based paints can ruin the look of latex paints applied on top of them.

Oil primer is the solution to this problem. It seals the oils in the old paint in place, and its own oil concentration is much lower — it will not discolour a water-based finish coat in the way that oil paint would.

Latex-Based Primers

With water-based latex paints being the industry standard today, it’s only logical that a similarly-formulated primer product is best for use with them. Latex primer dries quickly and has ample flexibility to resist cracking and peeling. Latex-based primers work well on most bare wood surfaces, including plasterboard, softwoods, concrete, brick, and metal. A latex primer will even out minor imperfections in the painting surface and conceal small stains (e.g. smoke, burn marks, ink, crayon, makeup, and so forth). They are a great way to paint new wood or bare wood surfaces.

Being water-based, latex primers are easy to clean up. They are also easier and safer to work with than other forms of primers. Many latex-based products are available in low or no-VOC (Volatile Organic Compound) formulations, giving off fewer fumes in the application process.

Shellac Primers

Shellac is a centuries-old sealing product that adheres extremely well to most interior surfaces, including new wood or when you paint bare wood, plaster, metal, and even plastics. Shellac primers dry quickly and work equally well with latex and oil-based finish paints. Shellac primer is a powerful sealant; it can cover serious stains like those produced by water and smoke damage. Shellac will even seal away the smoke smell left behind after a fire. Shellac is also great at protecting finish paint from the tannins that can seep out of raw wood.

The great downside to using shellac primers is that the application process is time-consuming and demanding. Shellac-based primers give off strong fumes; ample ventilation is a must. Using a shellac primer also obliges you to use denatured alcohol for thinning and cleaning during the painting process.

Applying Primer To a Wood Surface

Wood is the surface homeowners are most likely to want to paint and prime. Primer can be applied with a variety of tools, including brushes, rollers, and sprayers. Sprayers are the fastest, though they will need several passes to achieve adequate coverage. Brushes are the slowest, but they stretch the primer farther and achieve an even surface with minimal product required. Be sure to remove any note of the surface having been previously painted.

Any quality primer product will come with its own usage instructions; you should always follow these for the best results. Here are the steps involved in a typical primer application:

1) Thin the primer as per product directions.

2) Apply the first coat of primer with your preferred tool.

3) Let the primer dry for at least six to eight hours.

4) Lightly sand the dried primer using fine-grit sandpaper. If the directions call for the use of polishing paste, apply it now.

5) Apply two coats of primer.

6) When the second coat is dry, the wood is ready for finish painting.