The Differences Between Primer, Sealer And Undercoat Paint

The Differences Between Primer, Sealer And Undercoat Paint

Primer, sealer or undercoat? In the paint consumer market today, these three can paint a picture of confusion. But in order to maximize the final effect of your paint job and to ensure that the paint job is prolonged before any touch-ups are needed, you must know when to use each of these painting products. In this article, our Winnipeg exterior painting professionals break down the differences between primer, sealer and undercoat for you. We’ll explain when to use which so the next time these product names get tossed around, you’ll be in a position to make informed choices.

Undercoats are a subset of the primer category, and they both perform very different functions. Primers and sealers, on the other hand, are closely linked in terms of their functions, so real confusion can set in here. Let’s first learn the difference between primers and sealers.


The word primer comes from the Latin root word, prim, which means first. A primer then, is the first coat that should be applied directly to a bare substrate. Primers provide excellent adhesion and act as anchors for the new paint system. Good primers seal, hide and bond, forming a firm foundation for top coats. Since primers feature different binders as part of their ingredients, to provide the best adhesion, the primer should contain binders that are compatible with the substrate. Primers also inhibit moisture from reaching the substrate, thereby preventing subsequent coats of paint from sinking into the substrates. For staining timbers such as Cedar or Redwood, primers can help prevent stains from bleeding through into top coats and ruining the finished job


A sealer is designed to be used prior to, or as a substitute for a primer. Some sealer functions, like sealing off surface porosity and providing good adhesion between the substrate and the new paint, are very similar to that of primers. One of the biggest pluses of sealers, however, is that they can recondition an old surface that is unfit for painting. Traditionally the key role of a sealer has been to bind gypsum plaster. If you’re going to paint over weathered concrete or crumbly surfaces, we advise that you use a sealer as a base for the primer. Sealers can also be applied to serve as a barrier between incompatible finishing coats, particularly when coating previous finishes.


An undercoat is applied over a sealer or primer to further strengthen the functions of primers and sealers. These functions include providing a barrier to prevent moisture penetration, improving the bond between top coat and primer or sealer, providing a base that the top coat will stick to, and evening out small imperfections in rough surfaces. A general rule of thumb is that if you’re painting a new surface, always use a primer but if you’re painting over an existing surface that has been painted in the past, an undercoat will do well.

While painting a wall may seem simple enough at first glance, proper preparation and the right choice of products are extremely important. For the best results, you’ll want to hire experienced painting contractors who understand all the intricacies of different painting products.

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