Mist Coat vs. Primer – Is This the Same? We Explain the Difference

Though a mist coat is used to prime and seal fresh plaster in preparation for the top coat application, it would be incorrect to call it a primer. If this sounds confusing, you are not alone.

Many consumers do not know what to buy at the hardware store when confronted with rows and rows of primers, sealers, and undercoats. These terms should not prevent one from making an informed choice. This article will help clear that up.

You probably know that it is wise to prime any bare surface before painting it. You may also need clarification on the different types of primers, sealers, and undercoats in the market. Which one does what, and most important, which is the best choice for you?

If you wonder about the difference between mist coat and primer, this article has you covered. We will discuss that and a lot more to ensure these products no longer have you puzzled. Read on to learn more about:

  • The different terms used to describe prep coat products – primer, sealer, and undercoat
  • What is a mist coat?
  • What type of paint should you use for a mist coat?
  • How to mix a mist coat
  • How to apply a mist coat

The Difference Between Primer, Sealer, and Undercoat

Primers, sealers, and undercoats are collectively referred to as prep coats. The term is used to refer to all preparation coats that are applied on a surface before the paint. As the name suggests, these products are used to prepare the surface for the topcoat application.

1) Primer

Primers are the first coat that is applied to an unfinished surface like wood or metal. Most primers are off-white or white. White primers can be tinted to give the topcoat a richer shade.

Primers guarantee optimal adhesion by evening out your surface’s porosity and stabilizing powdery surfaces. Their job is to ensure that paint has no trouble adhering to the surface.

Different types of primers work best on various surfaces, e.g., wood, plaster, or drywall. Contractors use primers to serve many purposes, including:

  • Smoothing out any imperfections on the surface, e.g., cracks or pits
  • Stopping corrosion from damaging paint on metallic surfaces
  • Blocking out tannins and stains from affecting the appearance of the top coat.
  • Ensuring that the paint job is waterproof by preventing moisture from the surface from blistering or peeling away the top coat.
  • Preventing paint from suffering water damage due to fungus and mold.

2) Sealer

Sealers are types of primers that are typically used on masonry or plaster. They are usually clear or lightly pigmented. Sealers are manufactured to be used alongside or in place of a primer. Sealers to be used without a primer are intended to save time and money. Most sealers can perform all the essential functions of primers, with the added feature of sealing the surface.

The primary function of sealers is to prevent the topcoat from coming into contact with the surface. They also create a waterproof layer between the topcoat and the surface. When buying a sealer, be sure to ask whether it must be used after priming the surface.

3) Undercoat

Undercoats are used after the application of a sealer or primer. It serves to create a smooth surface for applying the top coat. Undecoats also come in handy when painting a surface from dark to pale. Technology has made it so that you can buy a three-in-one primer, sealer, and undercoat to spare yourself the hassle of these steps.

What is a mist coat?

A mist coat is a term used to refer to the first paint coat applied on bare plaster. It is made of a mixture of water, and Its purpose is to seal and prime the plaster surface to prepare for the topcoat. Plaster is very porous and needs to absorb the water for your topcoat to cover the wall evenly.

Anyone who attempts to paint plaster without beginning with a mist coat will end up with an ugly paint job due to adhesion issues. The bare plaster will absorb. You should avoid applying a mist coat on bare plaster that has been sanded.

Sanding plaster before applying a mist coat will leave a layer of dust that will reduce your top coat’s adhesion. If you need to get rid of lumps or drips of plaster, it is best to scrape them off. You can sand the surface after applying the top coat.

What is the Best Paint to Use When Making a Mist Coat?

Most contractors use contract matt for mist coats. Cheap paint will do the job right because all you need is a base for the top coat. You can spend all the money you save on a mist coat on a high-quality top coat.

Ensure you read the manufacturer’s instructions when buying paint to mix as a mist coat. These instructions will inform you whether the paint is suitable for a mist coat and in what ratios you should use it.

If you are tempted to skip the lengthy process of making and applying a mist coat on your plaster wall, you can use a water-based primer instead. Using the same brand and color for your mist coat and top coat is advisable but not mandatory. One coat of mist coat is usually enough to seal the plaster and prepare it for the top coat.

How to Mix Your Mist Coat?

You want to mix your mist coat such that it is very thin. The plaster won’t have enough water to absorb if you make a thick mist coat. A thick mix coat will not seal plaster properly because it contains insufficient water.

Every manufacturer puts instructions on the proper ratios of water to emulsion on the packaging of their product. The rule of thumb is that a mist coat should have the same consistency as a watery soup.

A general ratio is three parts of water to seven parts of paint. Some people also use a 50-50 ratio. If you cannot access the manufacturer’s instructions, you can try one of these rations. Keep in mind that your mist coat had better be too thin than too thick.

You should also ensure that the solution is thoroughly mixed and has an even consistency throughout. If you let the mist coat settle while painting, you may have to remix it to ensure the consistency is right.

How to Paint Mist Coat on New Plaster

  1. Before painting a mist coat onto new plaster, you should confirm that it is completely dry. While checking the plaster for signs of lingering moisture, inspect for signs of imperfections. Any bumps, drips, or defects will have to sand off to ensure you apply a mist coat on a smooth surface.
  2. Prepare your work area by covering furniture, laying dust sheets, and putting painter’s tape on your skirting boards.
  3. Sand out any imperfections on the plaster using sandpaper.
  4. Mix your mist coat by pouring the paint emulsion into a clean bucket and mixing it with water in the ratios recommended by the manufacturer. Using a measuring jug to ensure you get the ratio and consistency correctly.
  5. Using a roller, brush, or paint sprayer, apply your mist coat on the plaster. Paint sprayers are best left to professionals with experience handling them with care and efficiency. If you had rather use a sprayer, try renting one from your local hardware store. Ensure you read all the instructions on how to use the sprayer efficiently before using it. Rollers are the best option for DIYers. Though they are messier than brushes, they are quick and give a more even result. Use a 9-inch roller and apply your mist coat with smooth and even motions. Begin painting at the bottom and roll to the top. Ensure you do not roll over the same spot sparingly. If you decide to use a brush, a four-inch one is the best. Begin in the top corner and paint that section before moving on to the next.
  6. Once you finish applying your mist coat, leave a window open and allow the mist coat time to dry. Instructions on the packaging will inform you how long you need to wait for the paint to dry. Give it at least twenty-four hours and check the wall to ensure no damp spots remain. You can now prepare to apply your top coat.


A mist coat is not the same as a primer. It just happens to do the same job. It uses to prime and seal plaster for the application of a top coat. Anyone dealing with fresh plaster must apply a mist coat or a water-based primer to ensure the top coat adheres properly.

You do not have to buy expensive paint for your mist coat. Anything that will allow your fresh plaster to absorb water will do the job just right. One coat of mist coat is all you need to ensure your topcoat looks great and lasts long.