Here are scenarios when you need to use paint primer before applying the paint:
When Switching Color Shades
When you are going from a dark shade or colour to a lighter shade, you need to use paint primer to cover and prevent the darker shade from affecting the finish.
Also, when you are going from a bright colour like yellow or orange to a light colour, you need to use paint primer to prevent the brighter colour from reflecting through the finish.
Tip: When you want to switch colour shades, go for a grey primer.
When Switching Paint Sheens
Also, when you are switching paint sheens like when going from a higher sheen like semi-gloss to a lower sheen like matte or eggshell finish, you need to use a primer first.
When Working On A Fresh Material
When you are working on fresh material like fresh wood, concrete, plaster, or drywall, you should always prime it before painting.
This is because fresh materials are usually riddled with patches, imperfections, and sometimes, moisture. A coat or two of the right primer will prevent moisture and patches from affecting the finish.
When The Material Is Stained
If you are working on a material that is stained, filthy, or greasy, you should prime it first. For this, always use a stain-blocking or moisture-resistant primer.
When Panting Wood Trim
Wood trims usually need at least a coat of primer for the paint to last long on the wood.
When Painting A Slick Or Polished Surface
When painting slick or polished surfaces, always use a primer with good bonding qualities as the paint will not stick well to polished surfaces.
When Painting Porous Materials
Materials like wood, plaster, and drywall are porous meaning that paint can be easily sucked in. So to prevent wastage, seal the porous material with a few coats of paint primer.
When Painting Uneven Surfaces
When painting a rough or uneven surface, always use a paint primer first. If not, the finish will also come out rough.