Primers, sealers and finishes

Applying finish on primed metal fence.

A paint job from start to finish

As many know, a perfect finish often requires several layers of different products. The first layer applied on untreated surface is often a sealer or a primer paint. If one is applied, the other one is not needed. A finish is the top layer which is “finishing” the work. The finish can be applied for one or more layers depending on the product. Even though there are different types of products for different materials, their purposes are the same. That is why you should use primers, sealers and finishes products.

  • Sealer
    seals by forming a barrier between the substrate and finishing layer(s) preventing an unwanted effect of the substrate on the finish.
  • Primer
    forms the first layer when sealer is not applied and makes the surface even and ready for the finish. Often primers also increase adhesion and improve the finish’s properties.
  • Finish
    is the top layer(s) of the complete paintwork. Finishes come in many forms such as stains, varnishes, lacquers, paints, waxes etc.

Reasons to use primers, sealers and finishes

Wood

Applying wood primer on an outdoor fence

Applying wood primer on a fence

Bare wood is a difficult substrate material when it comes to applying only a finish. Therefore, use of a sealer or primer is a must. Wood is a porous material, which makes hard finish applications almost impossible without a sealer or primer. The best wood primer is usually oil-based due to the fact that it soaks into the wood and it sticks better than other primer types. The only disadvantage of most oil based primers is that they take a long time to dry: some even up to 24 hours. Fortunately, there are other faster drying high-quality primers on the market.

Metal

Sealers are useful when bare metal surface may have undesirable effect on the finish. Sealers also fill in gaps and holes in the surface more effectively than primers. Primers are also suitable for metal. A finish on bare metal tends to flake. Metal primers are designed to stick well to the surface and form a bond with the finish to let it adhere properly. Additionally, primers protect metals from corrosion for they do not let moisture through to the surface. Rusting untreated metals often require a sealer. Pre-treated and non-rusting metals (e.g. tin) only require a primer to improve adhesion.

Masonry

There are mainly two reasons to apply a sealer or primer on masonry work. Firstly, masonry often has a high pH level which may prevent a finish from adhering. Secondly, masonry sometimes forms efflorescence: white crystalline deposits that can occur on any masonry surface. Most masonry primers are resistant to efflorescence and prevent it from forming.


Easy to apply; just follow these 5 steps

Most sealer, primer and finish applications are done by roller, brush or spray. The big lines for the applications are similar. However, it is important to follow the product specific instructions. The following steps describe the basic process:

  1. Clean the substrate from dust and dirt preferably with a lint free cloth.
  2. If you are painting on top of old paint, sand the surface to let the first layer adhere better.
  3. Apply a primer or sealer on the completely dry surface and let it dry.
  4. Depending on the product, sand the surface and remove dust from it once the sealer/primer is dry.
  5. Apply finish on the dust free primed surface. Some finishes should be applied in several layers.

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