When is it critical to use a primer in painting?

Using a primer in painting is especially critical when dealing with surfaces that are porous or stained. This is because a primer serves several important functions that enhance the overall quality and durability of the paint application.

When a surface is porous, such as raw wood or drywall, it can absorb paint unevenly, leading to a patchy finish and requiring more paint than necessary. A primer creates a seal that limits paint absorption, ensuring a smoother, more uniform application of the top coat. Additionally, primers are formulated to block stains from bleeding through the final coat. For instance, if you are painting over a nicotine-stained wall or one with watermarks, using a primer helps to prevent these blemishes from showing through the new paint.

While it is recommended to use primer on various surfaces, including metal or when using dark colors for better coverage, the critical aspect revolves around addressing porosity and stains to achieve the desired finish and protect the underlying surface.