A primer is a base coat applied to a surface before painting. It is made up of resins and solvents but lacks the pigments found in finish paints. Mix the clear primer with dyes to obtain a tinted primer with better coverage. The primer base layer creates a uniform surface, improves adhesion, and blocks stains. It seals the porous surfaces from water absorption and provides a smooth finish. It also helps to apply a lighter paint over a darker one without any smudge marks. Primer saves your time and money as it covers the surface in fewer coats. It is widely used on drywall, wood, metal, masonry, and plastic surfaces.
| Property | Description |
|---|---|
| Purpose | Prepares and seals surfaces to ensure better paint adhesion and durability |
| Base Types | Available in water-based (latex), oil-based, and shellac-based formulations |
| Adhesion | Provides a binding layer for paint to adhere properly to various surfaces |
| Stain Blocking | Seals in stains (e.g., smoke, grease, watermarks, tannins) to prevent bleed-through |
| Surface Sealing | Seals porous surfaces (like new drywall or bare wood) to prevent uneven absorption |
| Rust Inhibition | Some primers (especially for metal) prevent rust and corrosion |
| Odor and VOCs | Water-based primers have low odor and VOCs; oil- and shellac-based ones may be stronger |
| Drying Time | Typically 30 minutes to a few hours, depending on type and surface |
| Sandability | Dries to a smooth, sandable surface for a flawless topcoat |
| Tintability | Can be tinted to match the topcoat color, improving coverage and final appearance |
| Compatibility | Designed to work under both oil-based and latex paints (check label for specifics) |
Here are the six most common types of primer:
Latex primer, also known as acrylic primer, is a low odor, less brittle, and fast-drying undercoat. This water-based primer is flexible and easy to clean. It contains low volatile organic compounds, which makes it best for indoor use. Latex-based primers remove the imperfections from concrete and brick surfaces to provide an even finish.
Oil-based primer is also called an alkyd primer due to alkyd resins as its primary binder. Unlike latex primers, it requires an extended drying time and also has high volatile organic compounds. These acrylic primers adjust according to temperature with contraction and expansion abilities. Oil-based primers are also known as “Stain Killers” due to their stain-resistant barrier. It is suitable for wood (especially tannin-rich woods like cedar), metal, and previously painted surfaces with superior adhesion. Don’t apply these acrylic primers on masonry surfaces due to their alkaline pH.
Shellac-based primer is famous for its stain-blocking characteristics. It is a fast-drying, odor blocker, highly adhesive, and durable base coat. Shellac-based primer is used under oil and water-based paints, though it can only be thinned with thinning agents. It is used to trap and block the smell of pet urine if it gets absorbed into porous surfaces. Shellac-based primer also minimizes the char marks, soot, and burnt smells after fire damage.
Bonding primers are made up of resin (polymer), hardener (polyisocyanates, amines, anhydrides), and solvent (water, acetone, ethanol). It also contains additives like silanes to promote adhesion and catalysts to speed up the curing time. Bonding primer is applied on glossy, slick, and hard-to-paint surfaces to ensure the paint lasts long. It reduces the need to sand the previously oil-painted surfaces.
Rust inhibiting primer blocks the supply of oxygen and moisture to prevent metal corrosion. It is made up of binders (alkyd, epoxy), pigments (zinc phosphate, red iron oxide, titanium dioxide), and extenders to adjust consistency. Rust-inhibiting primers contain corrosion-resistant chromates and form sacrificial anodes to protect the iron layer from rust. It is widely used to protect automotive parts, metal roofings, and industrial equipment.
Multi-surface or All-in-one primers stick well to all surfaces, including metal, wood, and plastic. It is composed of strong resin, solvent, pigments, defoamers, and biocides. It also contains binder, filler, and stain-blocking agents to prevent stains from bleeding through the topcoat. All-in-one primers are easy to apply as they are water-based undercoats.
Here is when and why to use a base coat:
New Surfaces: Use primer on new surfaces to prevent paint absorption and for a uniform appearance. It speeds up the drying time, leading to an even sheen finish. Water-based primers are also used to prime softwood (pine, fir, and spruce) due to their low density. Apply latex primers on plaster and masonry surfaces (brick, concrete, stone, and stucco) to reduce the moisture absorption and peeling paint.
Stain or Odor Issues: Primers contain stain-blocking agents to trap smells and hide the stains. Use latex-based primers to seal the stains of ink, crayon, lipstick, and smoke damage. Oil-based primers and shellac-based primers also prevent watermarks, nicotine, and tannin bleed.
Surface Color Change: Primers work as a barrier between two paint layers. It hides existing colors, especially when applying a lighter tone over a darker paint. Primers ensure the new color is true to its intended shade without any shadowing.
Glossy or Slick Surfaces: Primer contains high-density resins than regular paints, which promotes adhesion. It works well on tile, glass, vinyl, PVC, and laminates due to its quick drying time. Applying paint directly without primers leads to a non-reflective and dull finish.
Exterior Surfaces: Prime the exterior surfaces before painting to protect against moisture, UV rays, mildew, and temperature changes. It has a low porosity and doesn’t allow water to seep into the surfaces easily. Primers also prevent the efflorescence (salt deposits), making them best for the coastal residential areas.
Here are the four limitations of the primer:
No, paint primer is only good for repair and repainting work on small areas. It does not provide adhesion and sealing like dedicated primers due to its composition. Primers contain resins as their primary components, whereas paint primers also have binders, pigments, and additives with less resin quantity.
It requires 1 to 4 hours for a primer to set before painting, depending on the humidity and weather conditions.
Primer is not made to be a final coat. It’s not durable, washable, or UV-resistant. It leaves surfaces dull, chalky, and unprotected without a topcoat paint.
Yes, apply the primer to previously oil-painted or silk surfaces for durability and adhesion.
