When it comes to surface prep, there is a lot to say about it. As a matter of fact, the term surface prep is generally used to describe the processes applied to a surface before coating it, but it can also be used for welding and cutting.
In this article we are going to discuss surface prep using sandblasting as the basic example, since it is the most common method available.
What is surface prep?
Surface preparation, or surface prep, refers to processes used to clean and treat a surface prior to applying a coating like paint, powder coating, enamel, etc. Surface prep is important to ensure that the subsequent coating adheres to the surface and functions properly.
Most experts conclude that surface prep is one of the most important factors affecting the success of a corrosion protection system. The performance and durability of a coating is based pretty much on its ability to adhere properly to the surface, due to a thorough preparation.
What is the purpose of surface prep?
The main purposes of proper surface preparation prior to coating are:
Cleaning: Removes contaminants like dirt, grease, oil, wax, rust, mill scale, release agents, and other deleterious materials that can cause loss of adhesion or other coating defects.
Profile: Creates surface texture (peaks and valleys) through abrasion, etching, grinding, etc. This “profile” gives the coating material mechanical anchoring points to grip onto.
Deglossing: Dulls and roughens existing glossy coatings to improve adhesion of the next coat and avoid delamination or fisheyes.
Absorption: Provides uniform surface absorbency on porous materials like concrete so the coating is absorbed evenly without variations in sheen.
Corrosion Protection: Prepping removes surface corrosion and converts some metals like steel into phosphate or oxide layers that better resist further corrosion under the coating.
Repair: Detects and repairs defects in the substrate like dents, cracking, pinholes, seam gaps, warping, etc. prior to coating.
Contamination Prevention: Stops surface contaminants from getting trapped under the coating and causing defects like bubbles or craters.
Improved Appearance: Provides a pristine, uniform surface profile that allows coatings to better match the substrate for optimal aesthetics.
Proper surface prep is the foundation for every successful coating application. It helps the coating properly wet, flow, adhere, and protect on the substrate.
Different types of surface prep
Even though the scope of this article is highlighting abrasive blasting as the most important method of surface prep, we acknowledge that other methods are available. Some common surface prep methods include:
Abrasive cleaning
This is used to remove tough contaminants, such as rust, scale, and paint. Abrasive cleaning involves using compressed air with media like sand, grit, glass bead, aluminum oxide, or steel shot to abrade and remove contaminants.
Mechanical cleaning
This is the most common type of surface preparation. It is used to remove loose contaminants such as dirt, dust, and debris. Mechanical cleaning can be done using a variety of tools, such as brushes, scrapers, and power washers.
Chemical cleaning
This is used to remove contaminants that cannot be removed by mechanical cleaning. Chemical cleaning involves using solvents and other chemicals to dissolve and remove contaminants from the surface.
Thermal cleaning
This is used to remove contaminants that cannot be removed by mechanical or chemical cleaning. Thermal cleaning involves using heat to burn off contaminants from the surface.
Plasma cleaning
This is a specialized type of surface prep that is used to clean delicate surfaces and remove contaminants that cannot be removed by other methods. It involves using plasma to remove contaminants from the surface.
These are not the only methods for surface prep, but the most used by the industry. As a matter of fact, the methods used can be combined depending on performance needs, potential hazards, and cost.
SSPC, NACE, and AMPP
The Society for Protective Coatings (SSPC) and the National Association of Corrosion Engineers (NACE) are both organizations that created standards for industrial surface prep. Some of their standards coincided with each other, and people used to mention both at the same time. In 2021 they joined as a single organization: AMPP (Association for Materials Protection and Performance). Now, they have a website where they offer their standards and memberships.
Standards for Surface Prep
When it comes to abrasive blasting, there are standards that indicates the
The SSPC/NACE surface preparation standards are a set of joint standards developed by the SSPC and the NACE to provide guidance on how to prepare steel surfaces for the application of protective coatings. The standards are divided into four categories, based on the level of cleanliness required:
White metal blast cleaning (SSPC-SP5/NACE No. 1)
This is the most aggressive level of surface preparation and is typically used for applications where the highest level of corrosion protection is required. White metal blast cleaning removes all rust, mill scale, and other contaminants from the surface, leaving it a bright, silvery-white color.
Near-white metal blast cleaning (SSPC-SP10/NACE No. 2)
This level of surface preparation is less aggressive than white metal blast cleaning, but it still removes most of the rust and mill scale from the surface. Near-white metal blast cleaning is typically used for applications where a high level of corrosion protection is required, but the cost of white metal blast cleaning is not justified.
Commercial blast cleaning (SSPC-SP6/NACE No. 3)
This level of surface preparation removes most of the loose rust and mill scale from the surface, but some staining may remain. Commercial blast cleaning is typically used for applications where a moderate level of corrosion protection is required.
Brush-off blast cleaning (SSPC-SP7/NACE No. 4)
This is the least aggressive level of surface preparation and is typically used for maintenance applications where the existing coating is still in good condition. Brush-off blast cleaning removes loose rust and mill scale, but some staining and tightly adhered contaminants may remain.
Other standards
In addition to these four categories, there are several other SSPC/NACE surface preparation standards that address specific applications, such as the preparation of concrete surfaces, the preparation of stainless-steel surfaces, and the preparation of surfaces for powder coating.
The SSPC/NACE surface preparation standards are widely used in a variety of industries, including oil and gas, petrochemical, power generation, manufacturing, and construction. By following these standards, you can ensure that your steel surfaces are properly prepared for the application of protective coatings, which will help to extend the life of the coatings and protect the underlying steel from corrosion.
Here is a table that summarizes the key features of each SSPC/NACE surface preparation standard:
| Standard | Level of cleanliness | Typical applications |
|---|---|---|
| SSPC-SP5/NACE No. 1 | White metal blast cleaning | Applications where the highest level of corrosion protection is required, such as bridges, oil and gas platforms, and chemical plants |
| SSPC-SP10/NACE No. 2 | Near-white metal blast cleaning | Applications where a high level of corrosion protection is required, but the cost of white metal blast cleaning is not justified, such as pipelines, storage tanks, and ship hulls |
| SSPC-SP6/NACE No. 3 | Commercial blast cleaning | Applications where a moderate level of corrosion protection is required, such as structural steel, agricultural machinery, and automobiles |
| SSPC-SP7/NACE No. 4 | Brush-off blast cleaning | Maintenance applications where the existing coating is still in good condition, such as bridges, power plants, and water treatment facilities |
It is important to note that the SSPC/NACE surface preparation standards are only recommendations. The specific level of surface preparation required for a particular application will depend on a few factors, such as the type of steel substrate, the type of coating being applied, and the desired service life of the coating.
How to choose the right surface prep method?
The best surface preparation method for a particular application will depend on a number of factors, including 1) the type of surface, 2) the level of contamination, and 3) the desired outcome. Feel free to consult with us to determine the best surface preparation method for your specific needs.
The type of surface
Different types of surfaces require different surface preparation methods. For example, metal surfaces require different surface preparation than wood or concrete surfaces.
For painting metal surfaces, most likely you will need to remove any rust, corrosion, or other contaminants using sandblasting. Once the surface is clean, you may want to prime it to help the paint adhere better.
In the case of wood surfaces, you will need to clean and sand the surface to remove any dirt or imperfections. You may also want to prime the wood surface to help the paint adhere better. The sooner you apply the coating after the preparation, the better.
The level of contamination
The level of contamination on the surface will also determine the best surface preparation method. For example, heavily contaminated surfaces may require more aggressive surface preparation methods, like sandblasting, than lightly contaminated surfaces. Inspect the surface to determine the level of contamination.
Following the example, a ship hull most likely will be more heavily contaminated than some indoor staircase in the production plant. We both will need surface prep before painting, but the level of contamination is quite different.
The desired outcome
The desired outcome of the surface preparation process will also play a role in choosing the right method. For example, if you are preparing a surface for painting, you will need to choose a method that will remove all contaminants and create a smooth surface. If you are preparing a surface for welding, you will need to choose a method that will remove all contaminants and create a clean surface.
The type of coating to be applied also helps to define the preparation needed. High performance coatings require greater surface prep than decorative coatings.
What are the benefits of surface prep?
Surface prep takes a lot of time and resources, we know. It is calculated that about 40% of maintenance projects are related to surface prep. Nevertheless, here are some of the benefits of proper surface preparation:
Improved adhesion: Provides physical and chemical bonding to the substrate so coatings stick and endure rather than chip, peel and fail prematurely. It helps to ensure that the subsequent process adheres to the surface properly. This is important for applications such as painting, coating, and bonding.
Enhanced performance: It can improve the performance of the subsequent process. For example, proper surface preparation can help to improve the durability of a paint coating or the strength of a welded joint. Preventing even minor defects in the substrate prevents flaws in the finished coating like bubbles or craters.
Reduced maintenance: It can help to reduce the need for maintenance and repairs, by preventing corrosion and rust. Some methods convert metals to more corrosion resistant oxide layers underneath coatings.
Longer coating life: Prepping removes conditions that cause early coating deterioration like trapped contaminants, moisture or corrosion. Extends the service life of expensive coating systems applied over properly prepped surfaces.
Consistent appearance: Uniform surface profile and absorbency allows coatings to set and look the same across the entire surface. Clean, consistent surfaces allow coatings to fully achieve smoothness, gloss, color uniformity, and desired appearance.
Increased safety: Removing lead paint, oils, grease, and debris makes handling, spraying, and disposing of waste safer.
Faster application: Less coating material wasted trying to build up thin spots or correct absorption variations.
Get the help you need
For virtually any coating job, the time and effort invested into proper surface prep pays off with superior, long-lasting results. We are here ready to help you out with your surface prep needs. Feel free to reach out to us at your earliest convenience.
