There’s a lot of confusing information online as to whether or not primer is necessary. From years of experience, this is what I’ve learned about using primer when painting.
It’s recommended to use a primer before painting most surfaces. Without primer, porous materials such as plaster, drywall, and wood absorb paint before it’s able to dry. Using a primer creates a seal to enable the paint to adhere properly, resulting in a smooth, clean, and uniform finish.
As with most things, if you skip steps, you are going to regret it. The lack of a primer causes a range of issues that could end in a poor finish after the final coat of paint dries.
What Happens if I Paint Walls Without Primer?
Using primer saves you both time and money. Here are a few other consequences for not using it when painting walls.
Primer Seals the Drywall
Primer slows the drying of the paint and prevents the paint from soaking up into porous materials like plaster and drywall. Some new forms of composite drywall may not have the same issue with soaking up paint, but a primer is still advisable.
Most primers use a vinyl composite that seals the base material. It is also better to use two coats of primer than trying to use two coats of paint to protect the drywall from moisture. This means that you need to use less paint, which will flake off anyway if it goes on too thick.
Uniformity
Once the primer dries, you will notice that the vinyl in the primer evens out the surface – filling in scratches and dents in the wall. Since paint is much more expensive than a primer, it makes economic sense to fill these imperfections with the cheaper primer.
Adhesion
Primer helps the paint to stick to irregular, porous, and water-resistant materials. Drywall sticks much better to primer than paint, and paint sticks far better to primer than drywall.
The adhesion of paint on plaster or drywall is so bad that you may be able to rub it off with your hand. Primer also combats cracks and moisture that will push the paint off your wall.
Painting Damage Drywall/Wood
New wood will leach oils and moisture; this helps to keep the wood flexible and prevent cracking. You need to use a good primer to seal this moisture in and away from your paint.
Drywall with dents and cracks may need filling before you prime the surface since the exposed plaster will soak up the primer. Primer will cover smaller imperfections; it will help to smooth out the surface and make it ready for your paint.
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Is It Necessary to Prime Coat Wood Before Painting?
Old wood, more than new wood, will suck up most of your paint before it has a chance to dry on the surface. New wood will have chemicals present to prevent mold and to prevent the wood from cracking.
None of this is good for paint which needs a good base if you do not want chunks flaking off. Some primers can go over existing paint, giving you a new surface that covers up the color coming through from the old paint.
What Happens if You Don’t Prime Coat Wood Before Painting?
Standard woods, like pine, have deep and visible grains that are hard to sand flat. A single coat of paint will make the grain and knots more visible – a primer will fill in a lot of these imperfections.
If you try to fill voids in with paint, you will discover that you are getting through a lot of paint. Thick paint will also crack when it dries, look uneven, patchy. and it may even peel.
Why Is Primer Needed for Wood?
Primer smooths out wood grooves and fills in the small holes that you missed with the filler. The primer seals in the natural oils and moisture in the wood, keeping it from shrinking and splitting. Primer also forms a tacky surface that paint finds easier to cling to.
Is It Necessary to Prime Coat Metal Before Painting?
All metals corrode and form an oxide powder above the solid metal. Iron and steel will rust, and you will see over time that this rust will eat all the way through. Aluminum forms a thin layer of oxide powder that prevents the corrosion from progressing, which can make painting a challenge.
Many primers have a time limit on them; after 48 hours, there is a reduction in the adhesion offered by the primer. Though primer still offers a far better painting surface than no primer.
What Happens if You Don’t Prime Metal Before Painting?
Certain paint can also react to the metal and speed up the corrosion process, leading to flaking paint. If you decide to paint direct to the metal surface, then you need to use paint that states that it is for that purpose.
Using paint made for aluminum will reduce the chance of it peeling. But if you use an aluminum primer, it is going to be cheaper. If you use a primer, you can choose from a greater range of metal paints that will be less expensive than a metal-specific type.
Why Is Primer Needed for Metal?
Primer for metal is cheaper than special paints that do not need primer. The same as with painting woods, plaster, and other materials, a primer gets the surface ready for the paint. You save on good-quality paint by using more primer.
Metal primer will inhibit the corrosion from the surface reacting with the paint and give you a smoother surface to work with. The primer will also bond the paint to the metal better and make it less prone to scratches and chips.
What to Do if You Forgot to Prime Before Painting?
It depends on the type of paint and the surface it is on. Modern paints for metal include a form of primer that makes the surface ready. These ‘Primed Paints’ are often more expensive than the separate primer and paint, but it does mean that you are maybe able to get away with a single coat.
For a complete and consistent covering, you still want two coats of ‘Primed Paint’ on a metal surface. If the surface was clean and you used decent quality paint, the adhesion may still be good if you forgot to use a priming coat.
How to Fix Paint Without Primer
Metals without primers can form bubbles and peel off due to traces of rust, oil, or water. In some situations, you can fix paint by sanding the damaged area when dry and touching it up with new paint.
If the paint damage is over a small area, you will not want to be sanding everything off.
But if all the paint is peeling and bubbling up, the best thing to do is start again.
