The steps to remove powder coating
There are many reasons to remove powder coating. It might be due to a coating failure, the need to update and refinish, or cleaning racks and hangers after a successful coating, but sometimes you need to strip a coating. Though its durability is one of its greatest strengths, it is possible to remove powder coating from a substrate without destroying it in the process. You can remove powder coating with a chemical stripper, abrasive blasting, or extreme heat. There are even lasers designed to remove coatings.
In this article we go through the three main methods of removing powder coat, outlining the pros and cons of each, as well as a few tips for removing powder coating at home.
How to remove powder coating: The three main methods
The techniques used to remove powder coating come in three broad types. These three methods – chemical stripping, thermal stripping and abrasive blasting – each have benefits and disadvantages which may affect their suitability for your project. If you are removing coating in order to apply a new coat, remember: Surface preparation is paramount for an effective and successful coating application. A substrate that is dirty, greasy, insufficiently textured, or still has old paint can mean the difference between a valuable coating investment and a failure. Make sure you pick a removal method that will work with your future plans.
1. Chemical stripping
Chemical strippers come in hot and cold chemical stripping variations and methods. Hot strippers are essentially a caustic bath, kept at about 80°C . The coating will soften, dissolve, swell, and then fall off, or be washed off. Cold chemical strippers are usually solvent-based and can be applied with a brush or in a bath.
Chemical stripping is relatively fast and economical, and it will leave you with a uniform surface to your substrate once the coating is removed. If the part is more delicate, chemical stripping can be the the only way to go. The downside of chemical stripping is that the environmental, safety, and disposal issues often outweigh the benefits. They also do not leave a surface profile on the substrate for future coating ease.
2. Abrasive blasting
Abrasive blasting uses an abrasive medium and propels it at high speeds (with air or water) at a surface in order to strip the powder away. As well as crushed glass, glass beads, steel beads, dry ice, garnet, water and plastic are used. Aggressive blasting can remove the powder coating quickly, but damage the substrate, leaving it rough. A gentler blasting method will preserve the surface profile, though it does take longer. Abrasive blasting is done in a sandblast room or a sandblast cupboard, depending on the size of the part and the thickness of the coating being removed.
Abrasive blasting is the cheapest option of the removal methods, if your substrate is not out-sized or irregularly shaped. It is also the method that will leave the substrate with a surface profile. Abrasive blasting does take longer than the heat and chemical options, at a rate of about 30 seconds per square inch. It also requires the part to be washed prior to blasting as otherwise contaminations may become embedded in the substrate, compromising the integrity of the part.
Note: Abrasive blasting is also know under the general term “sandblasting”, as forms of sand used to be used as the abrasive media. Sandblasting like this is now banned as the silica dust caused is recognised as a carcinogen. The term sandblasting is still used, however.
3. Thermal stripping
Thermal stripping is the application of heat through a bake-off, burn-off, or fluidised bed stripping system. The heat breaks down the coating, leaving just an ash residue, which can be removed by water or blasting. The substrate needs to be able to withstand the temperatures required to destroy the coating, which can be as high as 650°C.
- Fluidized bed stripping system: This system uses a heated medium such as sand to transfer heat to the part. The coated part is lowered into a fluidised bed of heated medium (at 400°C) which both breaks down and carries away the coating. The part does not require additional cleaning.
- Bake-off stripping systems: Batch processes in which parts, hangers, or racks are loaded into an oven heated to 300-350°C – the temperature at which most powder coatings degrade and eventually ignite. After several hours only ash should remain.
- Burn-off stripping systems: At 550-650°C, this method uses the hottest temperatures to cause the coating to ignite quickly and burn off from the substrate (hence the name). It can take as little as 10 minutes for this process.
Using heat when removing powder coat is one of the fastest removal methods, and it does not have the disposal issues involved with chemical strippers as the remaining ash can be washed away with water. Like chemical stripping however, it will leave the substrate without a surface profile.
How do you know what powder coating removal method to use?
Knowing the substrate, your plans for its use, and the result you want from the removal process will lead you to the right choice of powder coating removal method. Below are some of the requirements you might have, and the advised methods to remove powder coating for each.
FAST REMOVAL – If you want the job done quickly, a burn-off system is the fastest option.
LOW COST – The cheapest stripping option is abrasive blasting, though keep in mind that larger jobs require longer time and therefore more work hours.
DELICATE PART – If your part is delicate or will not withstand high heat, chemical stripping is the best option.
POST-STRIP COATING NEEDED – If you are planning to apply a new coating and need a surface profile, abrasive blasting leaves a rough surface for further coating without extra steps.
LOW ENVIRONMENTAL IMPACT – Thermal stripping systems such as a bake-off system are usually fairly environmentally friendly. If environmental or health considerations are important, avoid chemical stripping.
STRIP GREASY/DIRTY PARTS – If you have parts, particularly engine or automotive parts, which are greasy or dirty and you don’t want the hassle of cleaning it, thermal stripping burns away the grease and dirt with the coating.
ALUMINIUM – Chemical stripping works for aluminium as it does not damage the underlying part.
STEEL – Abrasive blasting works well for steel substrates, as does thermal stripping under controlled conditions. Chemical stripping is also applicable.
WHEELS/RIMS – A combination of chemical stripping and sandblasting is often used to remove powder coating from wheel and rims.
Where to find powder coating removal contractors in Singapore
The process of applying a powder coat begins with the proper preparation of the substrate, including a cleaning step. This means that if you need to remove a powder coating, the place where it was applied is often the best option, as they likely have the necessary equipment already. Head to our powder coating overview page for a look at the powder coating companies operating in Singapore. If you are removing powder coating in order to recoat an item or part, our powder coating prices overview will guide you as to your best options.
Removing powder coating yourself with chemical stripper
The industrial powder coating removal processes outlined above will probably not help the do-it-yourself remover – it is unlikely you have a sandblast room out the back! If you are looking for how to remove powder coating yourself, you will need to use a solvent or chemical treatment. As noted above, this can be some nasty stuff, so you need to take every precaution when using it. When removing powder coating at home you should follow these steps:
- Make sure your work space is well-ventilated, with a solid floor (a garage is a good option). Wear safety clothing, including gloves, goggles and a mask or air-purifying respirator. Have a surface prepared to place the item on during the stripping process, such as a drop cloth or cardboard.
- Spot test the item with the stripper. Leave the stripper for the time recommended in the instructions, then test the powder coat with a scraper. If the paint is still stuck fast, try another spot test and allow more time for it to work. If this works, move ahead, otherwise you may require a different product.
- Apply the stripper. Coat the part being stripped and leave it for the same amount of time that you previously determined was needed for it to work.
- Scrape the paint. Once the time has elapsed, use a bladed paint scraper to remove the paint and the solvent. Dispose of the removed paint carefully. Go over the part with an abrasive pad or steel wool to ensure that all the paint and solvent is removed.
- Wash down the part. Rinse the part with water and wash it down with detergent.