What Goes First Primer Or Dehydrator

When it comes to painting, whether it’s for a DIY project or professional work, one of the key steps is to apply a base coat, which is usually a primer or a dehydrator. Both products play a vital role in preparing the surface for a new coat of paint, but which one goes first? Primers and dehydrators are not the same product, and their purpose, application, and functionality differ. Therefore, determining the proper sequence of application depends on the nature of the substrates, surface condition, and the finish type. In this article, we will discuss the differences between primer and dehydrator, their application procedure, the pros, and cons, and answer some FAQ’s on this topic.

What is a Primer?

Primer is a preparation coat that is commonly applied before painting to improve the adherence of the subsequent coating system. Primers are formulated to create a bonding layer between the surface and the paint, filling small pores, hairline cracks, and other surface imperfections, creating an even surface. Primers also prevent any tannin or stains from bleeding through the paint and ensure a uniform finish color. Besides, primers can improve the overall durability, adhesion, and longevity of the paint system while adding a protective layer against moisture, rust, and corrosion.

There are various types of primer available on the market, such as oil-based, water-based, shellac-based, and latex-based. The most common types of primers are oil- and water-based, which are also suitable for almost all substrates, including metal, wood, plaster, drywall, and masonry. The choice of primer may differ, depending on the type and condition of the surface, and the type of topcoat that will be applied.

What is a Dehydrator?

Dehydrator, on the other hand, is a specialized type of primer that is specifically designed for use on plastic, fiberglass, vinyl, and other non-porous surfaces. As the name implies, dehydrator eliminates moisture from the surface and promotes better adhesion by opening the surface to receive the subsequent coat of paint. Dehydrators are usually used in automotive refinishing and can also be used on other non-porous surfaces. Dehydrators do not fill pores or other surface imperfections as traditional primers do, but they provide a robust, chemical bond between the paint and the surface.

Dehydrators are highly volatile and dry quickly, making them ideal for use on large surfaces that need to be painted quickly. They also act as a mild solvent and wipe away oil, dirt, and other surface contaminants. However, due to their highly specialized nature, dehydrators should only be used on non-porous surfaces.

Comparison between Primer and Dehydrator

When it comes to using primer or dehydrator, it is essential to understand their different functions, applications, and limitations. Here we compare the two in terms of their purpose, application, and functionality:


A primer is used to create a bonding layer between the surface and the paint, improve adherence, prevent stains and bleed-through, and increase durability, protection, and longevity of the paint system.

A dehydrator is used to remove moisture from non-porous surfaces that can hinder adhesion and promote better chemical bonding between the surface and the paint.


Primer requires thorough surface preparation such as cleaning, sanding, and filling surface imperfections before priming. It may take some time to dry (from a few minutes to several hours). Apply the primer in thin even coats, allowing the previous coat to dry completely before applying another.

Dehydrator does not require surface preparation, but you must wipe carefully to remove oil, dirt, and other contaminants. Dehydrator typically dries in seconds to minutes. Apply the dehydrator in thin even coats, without allowing the previous coat to dry completely before applying another.


A primer fills pores and small surface imperfections, provides a uniform surface color, improves the bonding, durability, and longevity of the paint system, and protects against moisture and other external factors.

A dehydrator removes moisture from non-porous surfaces, opens up the surface to promote better adhesion, and protects against chemical fading and peeling.


Q: Can I use a dehydrator on a porous surface?

A: Dehydrators are designed for use on non-porous surfaces only, as they can only remove moisture from the surface and promote adhesion, which cannot be achieved on porous surfaces.

Q: Can I use primer and dehydrator together?

A: Yes, you can use both primer and dehydrator together to achieve the best results. Apply the dehydrator on the non-porous surfaces and apply the primer on top of that, as it will provide a more robust surface for the topcoat.

Q: How many coats of primer or dehydrator should I apply?

A: The number of coatings depends on the surface condition, type of primer, and topcoat. Generally, one to two coats of primer or dehydrator are enough, but you may need to apply more if the surface is heavily damaged or requires more preparation.


In conclusion, both primer and dehydrator play a crucial role in preparing the surface for a new coat of paint. Primer is ideal for porous surfaces, while dehydrator is perfect for non-porous surfaces. Knowing which to use first depends on the nature of the surface and the type of paint system you’re using. Primers and dehydrators work together to ensure an even, durable, and long-lasting paint system, and by knowing how to use them correctly, you can be sure of excellent results.