Painting Q&A: Grit Blasting versus Washing Parts

Q. Can you please explain the difference between grit blasting versus washing parts? Which is best?

A. This is an easy question if the finishing specification is defined. In most cases, we want the best finishing and adhesion we can get, but getting the ultimate can be very expensive and may not be required. If not required, is it a waste of money and effort? Only the customer can answer this. Once you know what is needed you can move forward.

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In grit blasting, an abrasive material is used to remove scale, rust, hard rough contamination on the surface of your product, which must be able to withstand such an aggressive process. It is not used to remove oils and it does not apply a conversion coating. It is the most basic method of cleaning and can be very effective depending on the finish requirement and product end use.

Be aware of a product that must be blasted. Wash off oil or grease before you blast. If you don’t, then all your grit will be contaminated and your part will still be dirty after you blast.

Washing is more accurately described as pretreatment because that is exactly what is happening: treatment of the product. The highest performance of coatings and product pretreatment is aqueous cleaning. A manual high pressure wand system may be the most effective for larger products.

Inline washers and pretreatment systems are the ultimate. When the cleaning method has been defined by a chemical company to match your specified requirements, the equipment supplier can build the proper pretreatment system. These systems offer consistency and repeatability for an excellent finish. Plastics and composites are typically cleaned with aqueous solutions to remove mold release agents and surface contamination.

Various suppliers can help you determine the best process for you once you have the following information:

• Define the finish requirement (do some reading!): Salt spray? Adhesion standard? Indoor use or outdoor use?
• Define the coating type: Water-based coating (requires excellent cleaning), powder coating (requires excellent cleaning) or solvent-based paints or coatings (slightly more forgiving of surface oils).
• Look at your budget, but make your decision based on the quality of your personnel and equipment.
• Quantity of parts: Is production required? Low production enables more flexibility, while high production can be much more challenging and more expensive.
• The area you have available for these processes.
• Talk to many suppliers, ask for proof and go look at other installations.

Global Finishing Solutions' Martin Powell has 33 years of experience in the finishing industry. He has bachelor’s degrees in marketing and business administration with a minor in international management. He has been published in several trade journals. For information, please call GFS at 800-848-8738.

Originally published in the November 2015 issue.