Interior-Painting Basics

Follow these tips for surface prep through top coat.


When applying a top coat of interior paint, mil thickness should be measured to ensure the correct dry-paint thickness.

Photo by: David Sacks

David Sacks

When applying a top coat of interior paint, mil thickness should be measured to ensure the correct dry-paint thickness.

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To avoid most of the headaches that can come with painting new interior walls, follow these basic guidelines for surface preparation, primer application and top-coat application:

Surface Preparation

Wall and ceiling surfaces should be completely dry before primer or paint is applied. Use a damp cloth to remove loose dust and dirt created during the drywall installation. If the drywall surface is wet, dusty or dirty, the paint may not coalesce, bond and flatten as it should.

Make sure the ambient temperature isn't too low for painting. Cold temperatures interfere with paint's ability to coalesce and bond; when it's too cold, the polymer particles don't have sufficient energy to move together. The air, the surface and the paint should all be at the manufacturer's recommended temperature, which is usually above 40 degrees Fahrenheit. Also, confirm that the temperature won't drop below recommended levels after painting for the time frame specified by the manufacturer.


Primer is the first coat of paint applied to the surface. It functions as an intermediary between the drywall and the top coat. A good primer seals the drywall to provide a more uniform surface for painting. Primer also helps prevent brush and roller marks in the top coat. When primer is used, the top coat is applied not to the drywall surface but to the primer. Think of primer as the foundation for a smooth, attractive interior paint job.

When priming drywall, the goal is to create a surface with uniform suction (absorption). The areas where joint compound has been applied don't absorb primer as quickly as the papered surfaces, and the result is a flatter finish in paper areas than in areas of joint compound. To solve this problem, primer has a lower solid content, which makes it less sensitive to the varying suction rates of different surfaces. In primer, the polymer particles coalesce and bond more easily than they do in paint, regardless of the surface they're applied to. Keep in mind that drywall primer doesn't hide flaws and isn't nearly as durable as paint. Its function is to create an even surface for paint by leveling out suction rates across the drywall surface.

Top Coat

The top coat is the last coat of paint applied to the surface. You may need to run the paint through a filter to remove dust and dirt from site work. Stir the paint and apply the manufacturer's recommended thickness of wet top coat, back-roll the paint and measure the mil thickness to ensure the correct dry-paint thickness. Back-rolling can enhance the uniformity of the paint coating. Depending on the paint system selected, applying two lighter top coats can provide a higher-quality and more durable finish than applying one heavy topcoat, which can run.

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