Cleaning & Pretreatment Primer Part Two: Meeting Standards

In the first installment of Cleaning and Pretreatment, we covered the basics of metal preparation. We discussed the techniques that you’ll use for about 75% of the finishing industry’s standards. For most job shops and small manufacturers, these metal preparation techniques are all you will need.

But what if you’re approached by a customer with a specific powder coating requirement that is quite demanding? Is your basic pretreatment process going to be enough? Probably not. 

If high-performance and long-lasting powder coating results are important to you and your clients, the only way to deliver those results is by upgrading your pretreatment process.  

Powder Coating Standards & Testing

When talking about standards, your customers will have one main question when it comes to the coatings you apply:

How long and how well does the coating protect the metal?

To find the answer, you have to test.

The primary industry test that measures how your coating (and, indirectly, your pretreatment process) performs is called a salt spray chamber test. During this test, coated samples are placed in a salt spray chamber where the samples are periodically sprayed with warm saltwater. These tests can last up to thousands of hours.

Typically, these painted samples have an “X” scribed or cut into the middle of the panel, so that bare metal is exposed directly to the salt spray. The objective of the test is to see how much rust or paint blistering occurs at the scribed X. The test item fails when rust or blistering creeps beyond a set distance from the X-shaped penetration through the coating. This failure measurement is usually ¼ inch, but in extreme cases where coating performance must be carefully monitored, the failure measurement can be small as 1/8″ (examples include some high-performance or military grade coatings).

All salt spray chamber tests will include a stated hour requirement and a failure definition. As an example, it might be that the X-scribed sample must withstand 500 hours of salt spray with no more than ¼ inch of creep. The test will then be run until the sample successfully reaches 500 hours or until the rust or blistering creeps more than ¼ inch from the X. If the sample fails before 500 hours, the lab will let you know how long the sample was tested before the failure point was reached. Typically, these results are provided in 25-hour increments. So, a failed sample might be rated at 425 or 450 hours. This is a standardized way of rating performance because most labs check samples only once daily.

Before performing a salt spray chamber test, check your customers’ specifications for the measurement and the standard. There are different standards used by the American Society for Testing and Materials (ASTM) that refer to salt spray hours, so make sure you get the correct documentation from your customer if you must pass a specific test.

Where Can You Get A Salt Spray Test?

Most manufacturers and job shops have their powder vendors perform salt spray tests. This is typically done free of charge for established customers. Of course, larger powder customers get preferential treatment when booking tests, so if you’re in a crunch, you can contact an independent lab that will test your samples for a fee. It isn’t uncommon when bidding on a large contract to use an independent testing lab to quickly demonstrate to a potential customer that you can meet their finish requirements.

Remember, 500 hours is about 21 days, so passing that test will require the sample to be in the salt spray chamber for three full weeks. A 1000-hour test takes a month and a half.

Some larger consumers of powder coated components, like John Deere and the U.S. military, have their own labs with salt spray chambers that they use to certify qualified suppliers. Before submitting your samples to one of these organizations, make certain the samples are representative of your capabilities and have been prepared correctly.

Pretreatment Guidelines For Coaters

Below is a general pretreatment guideline. Use it to determine the number of salt spray hours your current process can achieve and what to consider when increasing your coatings performance. This is only a guideline and doesn’t replace a salt spray chamber test.

  • 50 hours salt spray: as a reference, this can be achieved using clean metal (free of obvious rust, oil, grease, dirt, or other visible contaminants) with a single coat of a typical industrial enamel wet paint
  • 250 hours salt spray: clean metal with a single coat of a typical polyester powder paint
  • 500 hours salt spray: clean metal treated with a phosphate/non-phosphate chemistry, which is either dried in place or removed in one rinse step, followed by one coat of polyester powder paint
  • 750 hours salt spray: clean metal that is washed, rinsed, then treated with a phosphate /non-phosphate dry-in-place chemistry/sealer, followed by one coat of polyester powder paint

or

  • Clean metal coated with one coat of zinc-rich powder primer and one coat of a polyester powder topcoat
  • 1000 hours salt spray: clean metal that is washed, rinsed, treated with a phosphate/non-phosphate chemistry, rinsed again, sealed (or rinsed a third time, often using water that has been treated to remove minerals), followed by one coat of polyester powder paint

or

  • Clean metal coated with one coat of zinc-rich powder primer and one coat of a polyester powder topcoat
  • 2000-3000 hours of salt spray: clean metal that is washed, rinsed, rinsed a second time, treated with a phosphate/non-phosphate chemistry, rinsed a third time, sealed, rinsed a fourth time using deionized/demineralized water, followed by one coat of zinc-rich powder primer and one coat of a urethane powder topcoat

The greater the performance requirements for the coating, the more steps you need to take. Also, once you get to a 750 hour or greater standard, you will almost certainly need an automated pretreatment system with a powered conveyor moving parts through it at a fixed rate. While you can achieve 750 hours with a manual wash, it will take multiple chemicals and a good system that can switch between them without contamination issues.

Many smaller shops use a zinc-rich epoxy powder primer under a polyester topcoat to get good salt spray results without an expensive multi-stage pretreatment system. The only downside to this approach is that you must powder coat your parts twice. Properly applied and cured epoxy primer on clean metal can improve salt spray test results by 500 to 750 hours. 

Pretreatment Disposal

Increasing your pretreatment capabilities is great for your coating performance, but it adds a new problem to your shop – waste disposal. One of the main concerns we hear from customers who want to pretreat to a higher standard is that they’re worried about getting in trouble for violating waste disposal regulations. We’re constantly asked, “how do I get rid of the pretreatment waste?” The answer is to ask your local authorities.

Pretreatment waste can be costly to manage and mishandling your waste can have very real consequences for the environment. Here’s a list that should help save you from incurring penalties from local, state, and federal environmental agencies. Following these guidelines also protects your local drinking water supply from being contaminated by heavy metals or other harmful waste. Always check with local authorities BEFORE developing a waste disposal plan.

DON’T

  1. Don’t dump the waste into a lake, pond, river, creek, or other water source!
  2. Don’t dump the waste down a storm drain!
  3. Don’t dump the waste into a ditch or onto the ground!
  4. Don’t dump the waste into your septic tank!
  5. Don’t flush the waste down the toilet!

DO

  1. Do check with your local city and/or county water authority. If you are on a sewer system, they should have guidelines on what can go into the sewer system. Ask for permission – not forgiveness – in this situation. You may have to get some waste samples tested at a lab for their approval.
  2. Do check with your chemical supplier to get suggestions on the best way to dispose of the waste created.
  3. Do contact a local industrial plumber. He may have some good suggestions from other companies he has worked with in the area.
  4. Do contain the waste water in a basin or sealed concrete barrier. It may be possible for the water to evaporate and you can shovel the waste into a drum for disposal if you run a small operation.
  5. Do check local waste disposal companies and ask what they require to pick up waste water in highly restricted areas.

As we’ve pointed out in this article, there are very real costs associated with producing powder coated finishes that offer the highest levels of performance. For some shops these costs will be prohibitive, but for many others they represent a reasonable price to pay for the opportunity to attract and retain lucrative accounts. Because not all shops are equipped to provide 1000-hour finishes, the amount of competition for those jobs is smaller, and the profits are typically larger.

Which Pretreatment Option is Best For Your Business?

Adding steps to your pretreatment process can greatly expand your clientele, as many larger construction and military projects require exact coating standards. Showing you can meet those standards allows you to bid for more work at a higher rate. On the other hand, especially for smaller shops, the extra time it takes – not only to produce the next part but to manage the waste – may impact the bottom line. If you are wondering whether a multi-stage pretreatment process is right for your business, check out our Resources page for more information or give us a call and consult with one of our systems specialists.