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Proper Surface Preparation is Key in Metal Coating Processes

We’ve all seen it: orange peel, ugly surface imperfections, and foreign matter. All of these will ruin a would-be perfect paint job.

Protecting your metal surface is essential for any metal part, from cogs to chassis. A protective coating provides a smooth surface for lubricants and resistance to scratching, rust, and corrosion. It also makes your product much more attractive to potential buyers.

Surface preparation is critical in getting a smooth, long-lasting finish when coating a metal using paint, powder, or electrocoating.

So what are some methods of surface preparation, and which ones should you use to prepare your metal parts for coating? Below is a handy guide for the different methods of surface cleaning and preparation.

Need a hand deciding which coating is right for your product before you prep? This guide will help you decide.

Chemical Cleaning

A worker using a steam cleaning method for adequate surface preparation

This surface cleaning method involves using a solvent to remove oils and grease, prior coatings, loose rust, and many other soils from steel surfaces. A stiff brush removes any dust before the solvent cleaning takes place. Compressed air removes any dust afterward.

Solvents used in this method are applied in a few different ways:

  • Wiping with a cloth or brush
  • Alkaline cleaning
  • Steam cleaning
  • Volatile solvent cleaning

Wiping and volatile solvent cleaning are similar processes: a worker uses a cloth or brush to apply the solvent to the steel surface. Volatile solvents require a well-ventilated working area and repeated application of the solvent. Alkaline cleaning follows. When wiping on a non-volatile solvent, rinse the area after application.

Alkaline cleaning uses strong commercial detergents to scrub away all salt, acid, or other matter. Finish this process by washing down the surface with water.

Steam cleaning is often used in combination with alkaline cleaning. Steam is used to remove chemicals and other soils. 

All of these methods require the surface to be dry before any coating application.

Take care to follow all safety guidelines and instructions when using chemicals. To ensure proper safety and surface preparation, consult The Society for Protective Coatings (SSPC) surface preparation standards.

Hand and Power Tool Cleaning

Someone wearing a thick glove and preparing a metal surface by cleaning with a metal brush.

Hand tool and power tool cleaning both involve abrading the metal surface with a tool to remove rust, mill scale, paint, or other foreign matter before coating.

Sandpaper, putty knives, and wire brushes are all used to chip and abrade steel surfaces to remove loose contaminants. One drawback is that you can’t use this method to remove tightly adhered contaminants. Vigorous abrasion may result in scratching the metal.

When using power tools to prepare your surface, care must be taken to avoid creating burrs or sharp edges. The surface must not be polished or too deeply abraded. Too much scrubbing can compromise the strength of the metal and the adhesion of the coating.

Pressurized Water Cleaning

A worker on a cherry picker using a high-pressure water machine to clean a metal boat.

Jets of pressurized water are used to clean a metal surface with varying degrees of thoroughness but may not remove all contaminants. You do not add abrasives or particulates to the water before treatment.

In essence, this method is pressure washing the surface with pure water to remove loose contaminants. It may not remove tightly adhered substances like paint.

Abrasive Blast Cleaning

A worker using an abrasive cleaning method for Proper Surface Preparation

There are five types of abrasive blast cleaning:

  • White metal blast cleaning
  • Near white metal blast cleaning
  • Commercial grade blast cleaning
  • Brush-off blast cleaning
  • Industrial blast cleaning

White metal blast cleaning removes all particulates and coatings. This surface preparation method provides a uniform, “white” surface.

Near white metal blast cleaning is less thorough than white metal blast cleaning. It leaves some stains and flecks of older coatings behind.

Commercial grade blast cleaning removes rust, scale, and paint but leaves any staining from these on the metal.

Brush-off blast cleaning creates similar results to hand tool cleaning. This method removes loosely adhered rust and other contaminants.

Industrial blast cleaning removes all but tightly adhered rust, scale, and coatings. After cleaning, these should only cover 10% of the surface area.

Abrasive blast cleaning is the most thorough method of surface preparation, but it is also the most difficult.

You must take care to choose the correct abrasive for your material. Course abrasives can leave deep scratches on your metal. This makes coating adhesion difficult or impossible in some areas. Most applications use a grit between 18 and 40.

You can also combine this method with chemical cleaning to remove oil, grease, dust, and other matter before blasting. The most effective surface preparation uses tool cleaning and chemical cleaning before blasting. Multiple preparation methods remove any weld spatter, rust, or chemicals to ensure a clean blasting surface.

Removing all foreign particulates before blasting ensures a consistent surface texture that any coating will adhere to.

This method also requires a coating application on the same day cleaning is finished. This keeps dust and other particulates from landing on the surface of the steel before the coating application.

See this guide on surface preparation for more information on abrasive blast cleaning.

Surface Prepping Services

A worker using a sand blaster to prepare a metal surface for painting or coating

Preparing a surface for coating is a difficult job that requires abrasives and chemicals that are not recommended for general use. Preparing your parts for coating is best left to professionals.

Industry leaders like Minnesota Industrial Coatings can prepare your metal parts for coating. We will also help you choose the best method of coating and preparation for your purposes.

MIC uses eco-sensitive and quality-driven methods to deliver our best treatment to your product so you can give your best product to your customers. Want to know how to stop worrying about surface preparation and make MIC your manufacturing partner? Get a free estimate on our website.

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