When you set out to create any kind of finish, you learn that your prep work is the most important factor in getting good results. When it comes to powder coating, extreme cleanliness is absolutely critical. It’s easy to understand: If there’s any oil or dust on the item you’re trying to coat, that material is trapped between the powder and the underlying metal, and sooner or later (usually sooner) it separates from the metal and causes the finish to bubble and flake away.
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The challenge with cleaning is to get everything absolutely clean without turning your workshop or garage into a toxic waste dump.
Water and detergent-based parts cleaners are generally better to use in home shops than solvents. Water-based products create less hazardous waste, and they can deliver effective cleaning performance. Water-based products also eliminate a big fire hazard in your shop. Some gunk, however, responds better to solvents than detergents.
When it comes to getting good results with your powder coating, clean metal is the most important thing. In this book I spend a lot of time looking at cleaning methods because cleaning really is the majority of the work required to get good results with powder coat.
This intake plenum from a Ferrari 308 was in dire need of refinishing. Subjected to heat and grime, even in a Ferrari engine bay, the original paint is long-since cooked and darkened.
A little work with the Eastwood gel paint stripper and this plenum is ready to be coated. Dental picks came in handy to get the last of the paint out of nooks and crannies in this part.
This part required careful masking, but the prep work was the primary factor in getting great results like this.
Here’s what Oil Eater looks like when it’s mixed with water and placed in a benchtop parts washer. A pump sends detergent mix through the cleaning brush.
If you have an old parts washer in addition to your new one, you can have different cleaners in your washers for different kinds of cleaning chores. This one has seen a lot of use!
Heavy gloves that are rated for chemicals are good to have around. Nothing eats through them! Often, though, it’s a good idea to wear a pair of nitrile gloves under them.
Nitrile gloves are different from latex or other shop/surgical gloves because they are more resistant to more chemicals.
Eastwood makes a wipe-down cleaner called PRE Painting Prep. This is a great final wipe-down product to be sure that no oils (even skin oil) or dust is left on your parts before you coat them.
POR-15 also makes a final wipe-down cleaner that can be used to ensure that oil and dirt have no place in your powder coating operation.
In addition to grime (grease and dirt), you may also need to remove rust and old paint. No one solvent or process is best for all three offenders. If you are using solvents only, consider rotating your parts through different solutions. For example, use a parts dip to remove grease and dirt, then a paint remover, and finally a rust remover. Repeat if necessary. Rinse and dry the parts between solutions so you don’t contaminate one solvent with another or cause unwanted or even dangerous chemical reactions. If you are planning to media blast, cleaning the parts with solvent first speeds up the process.
Mechanical cleaning also has its place, as discussed in Chapter 4. When you have a lot of material to remove, you may want to start with one of those mechanical methods, such as a scraper, wire brush, sandpaper, media blasting with soda, sand, walnut shells, or glass beads. Then you may want to finish with a wet cleaner such as one of the solvents discussed in this chapter.
Chemical methods of cleaning metal vary widely, and the best ones to use vary based on the type of metal you’re cleaning and the type of gunk you’re cleaning off the metal.
Remember that any chemical intended to clean metal can be very toxic, and can “burn” your skin. Be sure to have several sets of chemical-resistant gloves near each parts washer. You don’t want this stuff on your skin. Always read the labels and follow the safety precautions that manufacturers recommend; add a good helping of your own common sense, too.
Cleaning Agents and Solutions
You can start with a bucket and soapy water, or a large can of solvent such as B12 Chemtool or mineral spirits. For a bit more money, you can buy a benchtop or freestanding parts washer that uses either water or solvent-based fluids. Many restorers use gasoline, biodiesel, or kerosene instead of the more expensive solvents in those cleaners.
If you plan to clean a lot of parts, and you have a sewer connection in your garage or shop, you can usually obtain a working dishwasher at very low cost and install it in your shop. Take out the top rack and you can fit some very large pieces into it and wash them with detergent and steaming hot water. This works very well.
If you have plumbing in your shop, consider installing a used sink. You can usually find them for free or for a very small price on craigslist or at a ReStore. Just be careful not to flush hazardous chemicals into the sewer system.
. A common dishwasher sourced from craigslist or ReStore makes a great home parts washer. The same rule applies: Be careful not to let hazardous chemicals drain into the sewer system.
If you build a simple cabinet around the dishwasher, you can use it as part of your workbench or for storage when you’re not washing parts. Plus, it adds stability to your parts washer.
Each of these options has some trade-offs, and that’s why many shops have more than one type of cleaning station. Many solvents dissolve or substantially weaken rubber parts, including the diaphragms in mechanical fuel pumps. Room-temperature water-based cleansers are less effective on grease and oil-based gunk, even with soap or detergent additives. Water can also pose a rust problem on some surfaces.
In general, you can do a good job with a small benchtop solvent-based parts washer and a bucket with some Simple Green or Oil Eater detergent and hot tap water. If you think you might need more, you can get a couple different benchtop units and fill them with different materials. Be sure to label each one!
Water and Detergent
The safest cleaners you can use are detergent and water. Water alone doesn’t strip dirt or many other impurities on the surface of a project, but detergents are effective because they dissolve oils and greases and hold dirt in suspension while you wash. Note that soaps can also be used, but they often leave behind more residue than detergents.
A small water heater can heat enough water to fill your bucket without running up the electrical power bill in your workshop. Some models fit under a standard counter.
A larger apartment-size water heater will provide enough hot water for any use you might have in a larger workshop. You can install it on a shelf to keep it out of the way.
Hot or warm water works better than cold water simply because so much of the gunk that needs to be removed from automotive parts is grease based. The more you can melt the grease and oily stuff, the easier it comes off. Pressurized water is also an effective way to get rid of buildup and even paint. So it stands to reason that hot, pressurized water with some detergent in it is the most effective way to use detergent-based cleaners. If you have a hose bib that delivers hot water, connect it to the pressure washer rather than connecting to it a cold-water source.
You can generally rent a pressure washer with a kerosene-fired preheater for the water and a siphon to pull in some detergent, but these are mainly used for big jobs such as cleaning the underside of a car or an entire engine. Still, if you have enough material to clean, it may be worth the rental fee from time to time.
Oven Cleaner
One of the more effective cleaners you can pick up in any grocery store is ordinary oven-cleaning foam. You simply spray it on and let it work, then wash it off with water. This is particularly good at dissolving gunk that has been baked onto your parts. But be aware that just because oven cleaner is readily available, it isn’t less nasty, and you really don’t want it on your skin.
Citrus-Based Cleaners
A variety of cleaners are based on citrus oils. You can purchase a spray-on cleanser similar to brake cleaner (TCE, TriChloroEthylene) but nontoxic. Some paint strippers are based on the same materials. These are indeed less toxic than the more chemically active products, but as you might expect, they do not work as quickly or completely. For light-weight jobs, these products are perfectly acceptable and kinder to your body and the environment.
Kerosene, Diesel, Biodiesel
Kerosene and Diesel fuel are oil-based, and they do a good job of dissolving oily crud. They are popular choices for benchtop and freestanding parts washers, and they’re safe to use inside your shop with reasonable fire precautions. Biodiesel is even better because the oils in it dissolve the grease better than the petrochemicals do. As with many other cleaners, keep heat, flame, and spark sources away from these flammable liquids.
Gasoline
I do not recommend using gasoline as a cleaning agent because it’s volatile and potentially dangerous. Although it effectively dissolves oily and greasy gunk, it’s also highly flammable and full of other chemicals, such as benzene and ethanol. Gasoline fumes are poisonous and easily ignite from any spark. If you do choose to use gas, never use it in an enclosed area.
Also remember that unsealed gasoline evaporates away, leaving behind a kind of varnish that you don’t want on your parts. Other products are far safer and work just as well.
Mineral Spirits
Mineral spirits, generally known as paint thinner, do a great job of cleaning oily residues. There is a difference between the two though. Paint thinner is less pure, and often includes other petrochemical ingredients. Mineral spirits are far more expensive, but also far more pure. Both of them are related to turpentine, but that’s a vegetable oil–based product.
Plain old paint thinner works well for getting rid of many paints and coatings. Be sure to leave it in the can and use it in a well-ventilated environment, as it quickly evaporates into fumes.
In general, mineral spirits are a much safer choice than gasoline for the same effect, and being purer it leaves less residue behind. Be aware that in an unsealed container such as a parts washer, mineral spirits evaporate in a few weeks, leaving an ineffective varnish-like liquid behind.
Acetone
This solvent, like gasoline, is best left out of a large-scale cleaning process. Acetone is volatile, ignites easily, and produces a lot of vapor. Generally speaking, a small can of acetone can be best used for spot cleaning of resistant coatings such as polyester or epoxy-based paints, tape residues, and glues, including cyano-acrylate, commonly known as Krazy Glue or Super Glue.
Chemical Paint Stripper
Chemical paint strippers (as distinct from a citrus-oil version) are typically based on caustic soda (sodium hydroxide) or methylene chloride. Both of these are extremely nasty materials, so you should be sure to work in an open area and use your best gloves. However, they quickly strip old paint and varnish from parts.
Furniture-grade paint stripper is pretty nasty stuff. Use this kind of product sparingly, but keep it in your arsenal. Citrus-based versions are less toxic, but they don’t work as effectively, especially on old and hardened finishes.
It’s worthwhile to have a can of Jasco (which is based on methylene chloride) in your arsenal, especially for cleaning parts previously painted with two-part epoxy paints. Don’t leave any methylene chloride on steel or cast-iron parts for very long, as it attacks those materials.
Methylene chloride is safe to use on aluminum parts. Do not use caustic soda because it attacks the aluminum.
Brake Cleaner
Trichloroethane (TCE) and per-chloroethane are used in brake cleaner sprays. These solvents are very effective at dissolving all kinds of grunge, but they’re expensive to buy in small cans. You don’t want to have prolonged exposure to these chemicals on your bare skin, or in an unventilated working area. It’s best to avoid them for major cleaning jobs, but good for removing oily residue in spots.
Rust Removal
Chemical rust removers are nothing short of amazing in their ability to clean even deeply rusted parts. The several options include acid-based naval jelly, acid-based etching solution, and urea hydrochloride–based rust dissolver. Of these, the urea hydrochloride, such as Eastwood Rust Dissolver, is the gentlest to use in your home shop.
These products may be painted on as a gel or used in liquid form as a dip. These products work by reacting with the iron oxide (rust), and they eat into the metal a little bit. They continue working as long as they are in liquid form on the metal.
Eastwood Fast Etch contains an acid that attacks the iron oxide that makes up rust. A bit of scrubbing with this product goes a long way in getting rid of rust, and you can neutralize it with plain water in your bucket.
Eastwood Rust Dissolver is made of urea hydrochloride, and it eats rust very quickly. Give it a little more time and it attacks the rest of your iron part and eats it away into nothing. You can neutralize this product with water; you want to do that as soon as the rust is off your parts.
Here’s a rusty part I picked up at the recycling center. I will treat it with Eastwood Rust Dissolver, and then give it a wire brushing to really make it shine.
I soaked the part in Rust Dissolver, brushing the fluid onto the parts not actually soaking in the pan. You can see that the rust is washing off quickly. I left the solution in the pan after this project, and in about a week it ate through the pan and leaked onto the workbench!
Most of the rust is now gone. The orange stain is not rust, but a residue of the cleaner. It just needs a little quick work with the wire wheel on the bench grinder to polish it.
Here’s the part, ready to coat. When your parts are clean, you should powder coat or clear coat them as soon as possible because the steel is completely unprotected and will start to rust again immediately.
All of these products can be cleaned up and deactivated with plain water. You still need to wear neoprene or nitrile gloves and eye protection when you’re using them. Also use them in a well-ventilated area, because they produce fumes. Combining rust remover with scrubbing works very well.
Phosphate Coatings
As part of your preparation for powder coating, consider creating a phosphate layer on your metal. Phosphating is a process whereby an acid-etch treatment leaves behind a layer of phosphate mixed with the underlying metal. The acid and other ingredients in the phosphate solution create a chemical reaction with the surface of the metal that leaves a layer of iron phosphate crystals on the surface of the treated piece.
The phosphate protects the project from rust and enhances the bonding of the powder coat and the underlying part so it makes a great surface for powder coating. The result is a coating that is better looking and more durable, so your powder coat project looks better and lasts longer. The easiest way to create a phosphate layer is to use one of the many products on the market. These are all based on either tannic acid or 2-butoxyethanol and may also include phosphoric acid. You can use dedicated phosphating solutions. You can create a phosphate layer on bare steel by spraying any weak phosphoric acid solution over it.
It’s best to use these products just before powder coating. You want to coat immediately after the layer is formed. If possible, do not even touch the part before coating.
If you’re working with aluminum, a similar process is known as chromating. Either way, it’s best to consider this an immediate precoating treatment. Don’t leave phosphate sitting open to the air for long periods of time.
Commercial Chemical Dipping
Chemical dipping is primarily the use of a big tank of the same sodium hydroxide solution in some paint strippers. Although you can purchase a small amount and do your own dipping, this process is generally the province of professionals. If you’re thinking of coating a whole set of wheels or other large parts (or a large number of small parts), professional cleaning may be the easiest and most cost-effective option.
This is an example of a part that should probably be taken to a professional metal stripping and cleaning business. It’s not that you can’t get rid of the grunge, rust, and paint by yourself, but it would be a lot of work, use a lot of product, and it’s heavy. It will cost less, be easier, and you get better results with the pros.
Dipping effectively gets rid of paint, body filler, and almost anything that isn’t steel. It does not dissolve lead, so if your part has some lead filler, you can use it. But the caustic soda completely dissolves aluminum, so don’t try it with anything that has aluminum content, such as pot-metal carburetors or other parts. Similarly, dipping agents, such as methylene chloride, are safe for aluminum but eat iron-based parts, so make sure you are using the correct chemical for the job at hand.
Project: Removing Multiple Paint Layers
A good time to consider commercial professional metal stripping is when you are removing factory paints or multiple layers. One cleaning project I undertook was a valve cover from an MG sports car that had several layers of paint on it. At least one layer was epoxy-based and did not respond to any chemical paint stripper. A flapper sanding wheel was not strong enough to cut the hard paint layer, so a wire wheel cup brush on an angle grinder was required to complete the job.
Once parts come out of a caustic soda bath, which has a chemical base, immersion in a muriatic acid bath neutralizes them. That’s the same acid added to the water in swimming pools. As a plus, the acid removes rust that a caustic bath can’t touch. Generally, the chemical stripping process includes steam cleaning and washing out of all chemicals used in the process. Be sure to ask about that when selecting a cleaner.
Step 1:
This MG valve cover had multiple coats of paint and lots of old glue and grunge on it. I wanted to see what it would take to really clean it.
Step 2:
Step one was paint stripper. I brushed on Eastwood gel stripper and it took the top layer of pink paint off in a thick, sticky paste.
Step 3:
I had to scrape off the pink goo. Whatever it was, it started setting up with the paint stripper gel and solidifying again! It could not be easily wiped away.
Step 4:
Once I got the pink goo off, I found a coat of light green paint. This was loosened with another coat of fresh gel paint stripper and scraped off.
Step 5:
Beneath the green was a coating of the original crimson color from the factory. This did not respond to the gel paint stripper at all, so I resorted to power tools to get down to the metal.
Step 6:
The sanding wheel did not get the job done on the flats, although it worked okay on the corners. I would have to get out the big guns.
Step 7:
A wire wheel cup brush spins at high speed and takes off anything that can possibly be removed. Be careful not to remove any more metal than necessary. Use this tool carefully on anything other than steel.
Step 8:
Here’s the valve cover with some clean metal finally showing! I still have a lot of work to do before this part is ready for powder coating.
Project: Powder Coating a Dirty, Unprepped Part
I, as well as many others, have stressed the importance of cleaning your parts, and this book is no exception to that chorus of unanimity. However, what most resources never show you is exactly why you need to clean every part thoroughly and what happens if you don’t. So, to settle the matter once and for all, I decided to powder coat an old, used part with no preparation at all.
I picked a coil spring from a rally car as a test subject. The spring was covered in the remains of old powder coating, rust, and a little dust.
Follow these steps:
Step 1:
Here’s a sample cleaning project with an object lesson. I decided to coat this spring without cleaning it to see what would happen.
Hang the old part with wire to facilitate an even coating.
I hung the spring using some safety wire so I could get all the way around the part for good powder coverage. I wanted to give this dirty spring every chance to get a good coat of powder.
Step 2:
You can see that I put plenty of powder on the dirty spring with the hope that it would cover up the rust, old paint, and grunge. Then I hung it in the curing oven and baked it until it was fully cured.
Connect your powder coating gun and follow all regular coating procedures. Spray a good, thick coating of powder on the part.
Step 3:
Here are the terrible results of the experiment. The new powder has not covered any flaws at all. Even the new powder coat will be flaking off in a few days. The experiment was an unqualified disaster.
Transfer the part to the oven and bake it, paying attention to proper curing time and temperature. When the part has cooled, take it out and inspect the results.
I put the spring into a foil tray and started with East-wood gel stripper to get the powder coat off. It took two coatings and a lot of wire brush scrubbing to get everything off.
With the second treatment, you can see some metal underneath. I wanted the spring to be perfectly clean this time around.
Here’s the cleaned spring (top), with its mate (bottom). Every bit of old powder, paint, and grunge has been removed. I wiped them down with PRE Painting Prep before I coated them for a second time.
And here’s the result when I did the job properly. I put about the same amount of powder on the springs the second time, and the results are spectacular. The lesson is simple and easy: Don’t skimp on your cleaning and prep!
Although powder coating flows into some scratches and low places to hide a few scars, a finished powder coating is not nearly deep enough to cover the highs and lows of active rust and old, flaky powder coat. The results look terrible, and although powder coating is tough and wants to stick to the part, if the powder sticks to rust, dust, or other paints that are already flaking, it’s going to come off sooner rather than later.
After the bad results were photographed, I went back and did the job right. I spent about two hours using gel paint stripper to remove all of the powder coat, and then I spent some time with a bench grinder and wire wheel to take off the rust and remaining coatings. I recoated and cured again, and with proper preparation I achieved a smooth, even coat that is suitable for use on a show car.
When powder coating suspension springs, you need to closely monitor the curing temperature. You must not apply excessive heat during the curing process. If you apply too much heat, the springs lose their temper and the spring strength can be reduced. Curing temperature must remain below 350 degrees F.
This project may be stating the obvious, but it was worth it to see exactly what happens when cleaning is neglected. The point is this: Do not fool yourself into thinking that you can get the same results without cleaning your parts. Powder coating is easy to do successfully, but good results depend on good prep work.
Written by Jeffery Zurschmeide and Posted with Permission of CarTechBooks
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