Home generalRemoving paint from wood, metal and plastic - how it works!

Removing paint from wood, metal and plastic - how it works!

  • The paint
  • Remove paint layers from wood surfaces
    • The grinding
    • The pickling
    • The use of hot air devices
    • The use of novel milling discs
  • Remove paint layers from metal surfaces
    • The grinding
    • The pickling
    • The use of hot air devices
    • Milling, roughing and brushing
  • Remove paint layers from plastic surfaces
    • The grinding
    • The pickling
    • The use of hot air devices
    • The use of novel milling discs
  • Remove paint stains and splashes

A new coat of paint or a new varnish makes things you love shine again. However, for this activity the preparations are a very important factor. A respectable surface will only succeed if the substrate has been evenly cleaned beforehand or even freed from old paint jobs if necessary.

"That should be repainted ..." is probably in many households a well-known statement. Before you actually devote yourself to such a project, some points should be clarified in advance:

  • Which materials are affected ">

    The paint

    A paint is usually a liquid coating medium, comes as an exception but since 1996 also powdered used. Essentially, paints consist of binders and fillers as well as the solvent, which ensures the liquid state and volatilizes after the painting process. However, modern paints are increasingly being produced on a water basis. What remains is a consistently solid film, which is primarily intended to fulfill a protective and decorative task. Many products are known under the terms "acrylic paint" and "epoxy resin paint", the latter is usually a 2-component paint.

    paint

    These paint colors are usually applied with a spray gun, which are either used by qualified personnel or industrially guided by robots. In the DIY sector, however, handy spray cans are widespread or the paint is applied by brush or even with a roller.

    Furthermore, a distinction is made between different processes for the completion of a lacquer layer:

    1. Oil varnishes dry and harden in air by reacting with oxygen
    2. Hardeners and binders react with each other in the case of 2-component paints
    3. Baking enamel harden and glaze at high temperature

    The following steps are used for most professional painting jobs:

    1. Cleaning and degreasing the surface
    2. Primer with primer
    3. Filler job to compensate for unevenness
    4. Applying the color coat
    5. Clearcoat for weather and lightfastness

    Finally, it should be noted that, of course, all the above criteria in industrial practice are optimally designed for the product materials such as wood, plastic, metal in order to achieve the highest possible adhesion and longevity of the coating. From all this information one can therefore conclude that the removal of such paint coatings is not an intended process and thus can take place only under difficult conditions!

    Remove paint layers from wood surfaces

    The grinding

    To anticipate, as a DIY method, grinding is still the best and most flexible method. Basically, one must accept that all types of wood are relatively soft and porous materials and thus an applied lacquer layer not only adheres to the surface, but can visually penetrate up to one millimeter deep into the material. This means that when completely removing paint layers, some wood material is also removed and edges and corners are slightly rounded.

    Sand wood

    For the first pass, coarse sandpaper of 40 to 80 grit may be used. For working on the wood surface with individual paint residues, grits of 120 to 180 are suitable and the final smoothing can be done with fine 240 grit paper. Depending on the size and size of the surfaces, these grinding operations can be carried out manually or with the help of machines. For small manual activities, cheap sandpaper sheets and the very practical sanding sponges that are available in many different versions are sufficient.

    For regular sanding a delta sanding machine is a good choice. Branded devices are already available for 100 euros. The advantages are:

    • very handy
    • Speed ​​control
    • suitable for surfaces and corners
    • Sanding sheet 3 positions
    • Connection for dust extraction
    Remove paint with delta sander

    If larger flat surfaces often have to be machined, an eccentric grinder achieves better work progress. The cost and benefits are similar to those of the delta grinder, however, the eccentric grinder is really only for surfaces and hardly suitable for edges and corners. On the other hand, both machines, especially the first operation with coarse grain size, have to pay attention to a moderate speed. This should be chosen so that the paint is still visibly "rasped". If the speed is too high, too much heat will be created, softening the paint and quickly adding the sanding sheet.

    Extenderschleifer

    In order to avoid unnecessary grinding effort, it makes sense to get an idea of ​​the overall condition of the paint surface before starting work and to clarify which changes are planned:

    1. if the paint surface is still good, a light sanding for a new coat of paint can be enough
    2. if the paint is already old and weathered, the loose areas should be removed with a spatula, wire brush or scraper before sanding
    3. If only individual paint splashes are to be removed, careful scraping with a scraper blade and a residual cleaning with a solvent is a possible method (see also last chapter)

    In general, the following safety measures should be observed when grinding:

    • Safety glasses for the eyes
    • Dust mask for nose and mouth
    • if possible work with suction devices
    • if necessary use ear protection

    The pickling

    Paint remover can also be used to remove paint colors on wood surfaces. However, since this is an aggressive chemical release process, the following safety measures apply when working with solvent-based paint strippers:

    • Safety glasses for the eyes
    • suitable breathing mask for the nose and mouth
    • resistant gloves
    • good room ventilation or work outdoors

    Alternative alkaline solutions are somewhat less problematic in this regard. In both cases, however, it makes sense before the Abbeizprozess with a scraper mechanical planing off as much paint material. Then only the remaining ink residues have to be removed chemically. Furthermore, it should be noted in this process that this can lead to discoloration of the wood surface. Likewise, a high amount of time has to be taken into account when pickling.

    Protective gloves, respiratory protection and safety goggles

    The products applied with a brush sometimes have to work for several hours and can then be removed with a spatula and disposed of. Then the wood surface must be thoroughly cleaned, dried sufficiently and sanded before a new coat can be made.

    The use of hot air devices

    To remove paint colors from wood surfaces, you can also use a scraper in combination with hot air. Through a hot air blower, the ink layer is heated until it softens and can be easily scraped off by means of a scraper blade. With this method, patience and tact are required, as for the softening hard coats quite high temperatures are required, but the wood is not scorched here. There is also the risk of burning one's fingers in this way of working. On the one hand, the necessary effort with this "Fönhilfe" is noticeably less than removing paint layers only by scraper blade, but on the other hand, additional finishing and grinding work will be required in this procedure as well.

    Remove paint with a hot air blower

    The use of novel milling discs

    Especially with larger and flat surfaces as well as a regular work assignment special tungsten carbide cutting discs can be worthwhile. The costs for the following product are around 100 Euro.

    This milling disc was primarily developed for the removal of colors, but is also universally applicable. This tool can be used with any standard angle grinder at speeds of approx. 9000 to 12000 rpm. Thanks to the open design, there are two major advantages here :

    • very low heat development
    • "Review" when sanding on the work surface

    This makes very efficient and controlled work possible.

    Note: The following chapters primarily describe the relevant factors compared to "Removing paint colors on wood surfaces"!

    Remove paint layers from metal surfaces

    In principle, the same advice applies here as with wood-based panels, but of course there are also differences. The advantage is the fact that metal surfaces are harder and more stable than wood surfaces and thus you can go something more powerful to paint removal. On the other hand, stoving lacquers and 2-component lacquers, which are very hard and tough, are more frequently used here. In the metal sector, glossy lacquers dominate, which, when repainted, make even the smallest dents and grooves in the metal surface visible.

    The grinding

    In order not to scratch the metal surface during the first grinding pass, one begins with a grain size of approximately 150 to 180. On the other hand, one should pay attention to a high degree of hardness of the abrasive grains.

    Abrasive paper hardness K180

    This is indicated by a letter in front of the grain (eg P 160), whereby the trend in alphabetical order goes from soft to hard. Thus, for example, A 40 is a soft and coarse, N 500 is a medium hard and fine, or S 180 is a hard and medium grain sandpaper. Depending on the objective for the metal surface, after the removal of the essential paint layers, the surface can finally be smoothed with fine grains and freed of the last color residues. When mechanically grinding curved surfaces, such as car body parts, an elastic backing pad should be selected to hold the grinding wheels so as not to plan flat surfaces. In addition to eccentric grinders, angle grinders are also used here. For inexperienced or optically final applications eccentric grinding machines are more useful, because it can be easier to avoid visible and disturbing sanding marks.

    The pickling

    This method is particularly suitable for angled metal structures whose surfaces are difficult to access for mechanical processing, such as corners, ribs and holes. To scrape the loosened paint layers then offer scraper and scraper blade with the appropriate shapes.

    Pick paint from metal fence

    The use of hot air devices

    Thanks to the temperature resistance and hardness of metal surfaces can be achieved with this method, a more effective work progress than on wood materials. As with pickling, appropriately shaped putties and scrapers are also helpful.

    Milling, roughing and brushing

    Particularly with coarse steel constructions, more powerful tools can be used for surface treatment. Especially for the universal angle grinder, there are a variety of possible attachments, such as milling, fan and grinding discs . When removing varnish layers, care must also be taken that the temperature development is as low as possible. This means that even at high speeds a constant mechanical milling process must take place and the color layers must not become soft.

    Remove paint from metal with the angle grinder

    Another way to remove colors from metal surfaces are brush attachments for angle grinders. The bristles consist of metal or hard plastics. Especially qualitatively simple lacquer layers or already weathered lacquers can be removed well with this method.

    Remove paint layers from plastic surfaces

    The material plastic is the most difficult material compared to wood and metal, in terms of removing paint. The two most important plastic groups used for painted products are thermoplastics and thermosets. Thermoplastic products are usually strong and flexible, but soften again when heated. At higher temperatures, a thermoplastic can lose its dimensional stability and even become liquid again. On the other hand, thermoset products are very hard and can not be deformed after curing.

    The grinding

    In principle, both mentioned plastic groups can be ground, whereby, of course , particular attention must be paid to the temperature-specific parameters such as pressure, speed and grain . If in doubt, a trial loops at uncritical places makes sense to opt for the appropriate procedure. So for thermoplastics tend to start with low pressure, low speed and medium grain size or you first apply the manual operation. Lacquered thermosets correspond in many ways to the wood versions and therefore the same advice applies.

    The pickling

    Here is a similar differentiation as when grinding. In principle, paint colors can also be removed from plastic surfaces with this method, but it is not foreseeable how many of the commercial plastic products react in detail to this chemical process. So it is advisable to try it out carefully. Very thin-walled and flexible plastics are less suitable than stable and hard plastic products.

    Paint Stripper

    The use of hot air devices

    With this method one can draw a clear dividing line: For thermoplastics plastic products this procedure is absolutely unsuitable . On the other hand, surface treatment of thermosets can be based on the procedure for wood. However, one essential point remains to be considered. The wood surface reacts at high temperatures first with slightly scorched optics, which can be repaired by grinding mostly again. But when working with a hot air gun, up to about 600 ° C can occur, whereby the melting points of many thermosets are significantly lower. Furthermore, it should be noted that the achievement of this melting temperature is often achieved without visible announcement and the surface is then quickly damaged.

    The use of novel milling discs

    Again, you can clearly distinguish between the two plastic groups. The method described for wood can be used equally for flat and hard plastic surfaces, ie only for thermosets and not for thermoplastics.

    Remove paint stains and splashes

    When improperly painted, the side effect often occurs that adjacent surfaces or objects are soiled with paint. In this case, fast action has the highest priority, because each varnish bonds more firmly to the surface as it progresses and hardens accordingly. The following measures are helpful with fresh color spots:

    turpentine
    • First carefully wipe paint splashes, stains or drops with a clean cloth or kitchen paper without unnecessarily increasing the color area.
    • in the case of water-soluble paint, clean the remaining contamination with water and possibly with some household detergent.
    • For chemical paints based on chemical solvents, the remaining contaminants should be cleaned very carefully with solvents or solvents that are initially weak, so as not to attack the original surface. If necessary, the following remedies can be tried one after the other:
      • spirit
      • Cleaning alcohol (96%)
      • benzine
      • white spirit
      • acetone
      • Nitroverdünnung

    Note: Acetone and nitro dilution can also attack or dissolve existing paint surfaces!

    Tips for quick readers:

    • first analyze the coated material
    • then check the paint layer to be removed
    • Pre-clean with a spatula, brush or scraper
    • Test the selected measure in advance for suitability
    • Protective measures: glasses, respirator, ear protection, gloves
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