Does High-Gloss Paint Need an Undercoat?

High gloss paint finish in a New York residence

Surfaces painted with a high gloss have a smooth, shiny and reflective appearance. High-gloss paint is ideal for adding dimension, detail and interest to any surface, including interior and exterior doors, cabinets, trim and high-traffic areas.

Preparation is crucial when using high-gloss paint. Undercoats, sanding and priming are often necessary to achieve a high-quality finish. Read on to learn more about undercoats and when to apply them.

Primer vs. Sealer vs. Undercoat

Primers, sealers and undercoats are three preparatory coatings that serve different functions. Let’s define each to help you understand their role and purpose in the painting process.


A primer is the first coat of paint applied to a surface. Primers improve porosity to ensure subsequent paint layers adhere strongly.

A coat of primer can also:

  • Neutralize stains
  • Prevent seeping or bleeding between layers of paint
  • Prevent the formation of rust on metal surfaces
  • Flatten out imperfections on uneven surfaces
  • Form a barrier so moisture can’t reach the topcoat
  • Prevent the development of mold and fungus


Sealers are a special prep coat to use with or in place of a primer. A sealer’s primary purpose is to provide good adhesion between the surface and the primer or topcoat. When using a sealer, apply it before the primer.

Sealers are excellent for reconditioning old surfaces to make them suitable for painting. Sealers fill in porous areas on the surface to prevent the topcoat from soaking in. They also create a water-resistant shield between the surface and topcoat.

Additionally, sealers can help retain any waxes on the surface and prevent the painted surface from staining.


An undercoat goes on after the primer. Undercoats fill any remaining imperfections, creating a flat, level and neutral-colored base for the topcoat to adhere to. Undercoats also help lighten a surface when transitioning from darker to lighter colors.

Undercoats are pigmented and work best with enamel topcoats. When layered over a primer or sealer, undercoats fortify and bolster their function. The resulting foundation is a robust and moisture-resistant barrier that forms a solid base for additional coats of paint.

Bucket of high gloss white paint

Does High-Gloss Paint Need An Undercoat?

It’s generally best to use an undercoat before applying high-gloss paint. Our professionals apply an undercoat before high-gloss paint in the following situations.

  • When there is a dramatic color change: Undercoats conceal the existing paint’s hue, preventing it from interfering with the new high-gloss paint color. You can choose shades of undercoat that closely match your topcoat to ensure the final color is full and rich.
  • When the surface is bare, in which case you’ll also need a primer: Bare surfaces need lots of preparation to support a quality, long-lasting paint job.
  • When the surface  is in poor condition: An undercoat will help the primer cover and fill in flaws in the existing paint.
  • When the existing paint is a gloss: Existing gloss needs some additional preparation before adding fresh high-gloss paint. An undercoat can help prevent it from peeling in the future.

In addition to using an undercoat, it’s almost always necessary to sand the surface before applying gloss paint. Sanding removes imperfections and adds adhesion by creating small, rough ridges for the color to bond to.

Regarding high-gloss paint undercoats, the bottom line is that it never hurts to apply one. If you’re unsure whether your circumstances warrant an undercoat, play it safe and use one.

Should You Prime Before Painting With High Gloss?

Whether you need to prime before painting depends on the surface. For example, metal surfaces need a primer before adding high-gloss paint. Otherwise, the color will flake off almost immediately.

Wooden surfaces may need priming and undercoating before painting, depending on their condition. For walls made from plaster or concrete, primer prevents them from absorbing the paint.

You usually only need to sand and coat previously painted before applying new high-gloss paint. You can spot-prime any bare or troublesome areas.

Following are a few additional scenarios in which a high-gloss paint primer is necessary.

If the Walls Are Porous

Primer is a necessity when painting porous surfaces. They can absorb moisture, oil, stains and odors if there isn’t a barrier to protect them.

Examples of porous surfaces include unstained or untreated wood and drywall. These will absorb paint without a coat of primer to seal them.

If the Walls Are Glossy

Paint cannot easily adhere to high-gloss walls. Whether your walls are shellacked wood paneling or covered with gloss paint or enamel, they’ll need priming and sanding before you apply indoor gloss paint on walls. This step ensures the surface has enough texture to grip the primer and paint.

If the Walls Are Stained

If your walls have stains from water damage, smoke or a kid’s art project, priming is a necessary first step. Primer acts as a blocker, sealing stains so they won’t permeate the new paint.

Before applying primer to stains, you must address the issue that caused them in the first place. If your walls have water stains, repair the leak before painting. Unaddressed leaks can cause mold growth, which is a health hazard.

If the Walls Have an Odor

If previous residents had pets, smoked, cooked pungent foods or dealt with a fire, the walls might have absorbed and retained those scents. A primer can seal in strong odors and eliminate them so they don’t return.

Regular paint formulations don’t permanently keep odors away, so don’t skip the priming step when sealing out strong smells.

If You Are Drastically Changing the Color

Priming is necessary when switching from a very dark to a very light color or from one vivid hue to another. Heavily saturated paint colors can show through paler, lighter shades. Priming these colors first means you won’t need several coats of paint later to cover them up.

High gloss paint contractor in New York

Trust Your Painting Needs to Shoreline High Gloss

We understand what it takes to produce a beautiful, long-lasting paint job at Shoreline High Gloss. Our family-owned company delights homeowners in New York City and Palm Beach, Fla., with our expertise and professionalism.

High-gloss finishes are our specialty, so if you’re ready to take your home to bold new heights, contact us today.