Detecting Defects in Surfaces and Surface PreparationUpdated: October 26, 2023
Surface preparation is a crucial step that must precede an industrial coating process. While surface prep includes general cleaning operations, it’s also your chance to identify surface defects and take preventive measures before applying your coating. Understanding the possible defects and the coating problems you can prevent with surface preparation will save you time and money lost on reworking a piece.
The Importance of Identifying Surface Defects Before Coating
Surface defects can result in a poor-quality coating that affects the overall performance of your metal surface. While these industrial coatings are designed to prevent corrosion and withstand hazardous environments, a poorly applied finish will be incapable of providing the full protection you’re looking for.
These coatings are a time and cost investment that is only worth it when they perform well. To get the best possible performance from your industrial coatings, you need to identify surface defects and prepare your surface appropriately. Surface defects can stand in the way of proper adhesion between the finish and the substrate. This adhesion is critical for creating a durable, protective barrier that lasts in corrosive environments.
Types of Coating Defects You Can Prevent
Coating defects can look different depending on the type of surface defect you may have missed during preparation. Some common defects include:
- Adhesion failure: Adhesion failure occurs when the chemical bond is broken between your substrate and coating at the bonding interface. This typically occurs when your surface is not properly prepared. You need a consistent anchor pattern across your substrate to ensure adhesion, and surface defects can stand in the way of this consistency.
- Delamination: Delamination is peeling that occurs after your coating has cured. The most common reason for this peeling is poor surface preparation. When your surface has inconsistencies like porosity or undercut, the coating cannot properly adhere during the finishing process. Delamination can also occur if the surface is dirty or contaminated before application.
- Undercutting: Undercutting is peeling or blistering caused by exposed and rusted areas on a substrate. This rusting occurs anywhere the substrate was left exposed after applying the coating. When a surface is uneven, some parts of the substrate will have a thinner coating and a greater vulnerability to rust.
- Pinpoint rusting: Pinholing can lead to an uneven coating layer, leading to rust development at the pinholes.
Know What You’re Looking For
Understanding the types of coating defects is one thing. Knowing the types of surface defects that cause these coating problems is another. Generally, there are three categories of defects to consider when working with metal surfaces:
- Imperfections from welding: Welding-related imperfections include spatter, slag, ripples, undercut, porosity and end craters.
- Edges: Rolled edges and thermally cut edges often need surface preparation before coating. Defects to watch for include rough edges that may have been left behind following a fabrication process like punching, drilling, sawing or shearing.
- Steel surfaces: Pits, crates, grooves, gouges, indentations, roll marks and other imperfections are common on steel materials that haven’t undergone extensive stock removal.
Inspection as Part of Your Surface Prep for Sandblasting Routine
Before blasting for surface preparation, the abrasive blaster has the responsibility of inspecting the materials to detect defects. In addition to a visual scan for cuts, scoring and other indicators, it’s necessary to touch the surface with a gloved hand to feel for indentations and protrusions.
There’s a grading system to take into account when you’re detecting surface defects. This system will help you determine the level of preparation you’ll need to reach and whether blasting or significant grinding and re-edging will be required. Sometimes, there will be two different grades for each side of the material depending on how it’s going to be used. The classifications are as follows:
- P1 Light Preparation
- P2 Thorough Preparation
- P3 Very Thorough Preparation
Shot Blasting Industrial Surface Preparation
Detecting defects in surfaces before painting and coating is only half the battle. The next step is to perform abrasive blasting to eliminate imperfections and deliver a surface in line with its preparation grade. An efficient, economical way of doing so is with shot-blasting, which offers a faster process than many other methods, a smoother surface and the greater ability to customize finishes.
Blasting is not only useful in blending away defects and smoothing out rough spots but also for cleaning contaminants and achieving a textured final looking. Industries that utilize abrasive blasting range from manufacturing, automotive and construction to industrial painting and coating, electronics and steel and mining.
Getting Help With Steel Surface Preparation
The experts at Finishing Systems can help you identify surface defects and handle surface preparation with precision. As leaders in the finishing industry, we offer an excellent selection of abrasive blasting media, supporting products and specialized services to support your operation.
Get in touch with us today to speak with one of our expert representatives about our surface preparation solutions.