Leo Martínez
Painting over pre-painted surfaces is a common practice, especially when dealing with walls, canvases, and miniatures. While it is possible to paint over existing paint, it is important to ensure that the previous paint is intact and not flaking or peeling. If the previous paint is not in good condition, it may need to be stripped or sanded before repainting. In some cases, a primer may be necessary to ensure proper adhesion and coverage, especially when using oil-based paints over latex or significantly changing the paint colour.
Characteristics and Values Table
| Characteristics | Values |
|---|---|
| Surface Soundness | Cut a small X through the existing paint, press sticky tape over it, and rip it off. If the paint comes off, it is unsound and should be removed. |
| Surface Preparation | Scrape off all loose and flaking paint and ensure the surface is dry. |
| Paint Adhesion | If there is poor adhesion, you may need to strip the paint. |
| Stripping Methods | Sanding, scraping, or using chemical strippers. Wear appropriate protective clothing and equipment. |
| Lead Paint | If the surface was painted before 1990, it may contain lead. Have a professional test and remove it. |
| Primer Usage | If covering a dark colour with a light one, use a primer to save on paint coats. |
| Primer Alternatives | Use paint & primer in one or fill holes and spackle and sand the wall before painting. |
| Paint Types | When covering latex paint with oil-based paint, use a primer formulated to bond with the new paint. |
| Paint Thinning | Avoid thinning acrylic paints beyond the recommended ratio (e.g., 1:1 for some brands) to maintain adhesion. |
| Paint Layering | Apply multiple thin layers to build up the desired sheen, especially when using varnish. |
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What You'll Learn
Test the surface adhesion of the existing paint
Testing the adhesion of existing paint is an important step to ensure that your new coat of paint will adhere properly. There are several methods for testing paint adhesion, each varying in complexity and the tools required.
One simple method is to purchase a small amount of the paint you plan to use. Choose a non-tinted version so you can return it if needed. Apply a small amount of the paint to an inconspicuous area and allow it to fully dry. Then, take a piece of high-quality masking tape and stick it onto the painted area. The stickier the tape, the better. Finally, remove the tape. If no paint comes off with the tape, the adhesion of the existing paint is strong, and you can proceed with painting.
Another method is the knife test, which can be performed with a utility knife. This test involves cutting an X-shape or crosshatch pattern through the film of the paint down to the substrate. Then, apply pressure-sensitive tape over the cuts and remove it by pulling it off rapidly back over itself at an angle of 180 degrees. The adhesion can then be assessed on a scale.
A more complex method is the pull-off adhesion test, which can be performed using a portable adhesion tester, such as the PosiTest AT. This test involves affixing a loading fixture, commonly called a dolly or stub, to the coated surface using an adhesive. The tester is then attached to the loading fixture and gradually applies tension until the dolly is pulled off. The force required to pull off the dolly or the force it withstood yields the tensile strength in pounds per square inch (psi) or mega Pascals (MPa).
It is important to note that the choice of testing method may depend on various factors, such as the previous coating, surface condition, and desired results. Additionally, some methods may be more suitable for specific types of surfaces, such as the scrape adhesion test, which is typically performed on smooth, flat panel surfaces.
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Scrape off loose paint and sand the surface
When repainting a surface, it is important to scrape off loose paint and sand the surface to ensure the new paint adheres properly and the finished product looks polished. Here are some instructive tips to guide you through the process:
Firstly, determine the condition of the existing paint. If the paint is well-adhered, scraping and sanding may not be necessary. A simple test is to cut a small 'X' through the paint, apply tape over it, and then rip off the tape. If the paint comes off, it is unsound and should be removed. Alternatively, you can try washing the surface with a cleaning solution or power washing to remove any dirt or loose paint chips.
Once you've determined that the paint needs to be scraped, use a suitable tool to carefully scrape off all the loose and flaking paint. Be thorough and ensure that the surface is clear of any paint chips and debris. The goal is to create a smooth and stable base for the new paint to adhere to. If there is stubborn paint that won't come off, you might need to use a chemical stripper or a product like "Peel Bond" by XIM, which acts as a bonding primer to smoothen the surface.
After scraping, the next step is to sand the surface. Sanding is especially important if you plan to use glossy paint, as it ensures the new paint sticks permanently. Use sandpaper or a sanding tool to smooth out the edges and create a uniform surface. Pay close attention to the areas around entrances and patios, as these may require extra sanding to achieve a seamless finish. Remember to wear the appropriate protective clothing and equipment during the sanding process.
Finally, once you've finished sanding, clean the surface to remove any dust or residue. You can use a blower, a large paintbrush, or a cloth with rubbing alcohol or water to wipe down the surface. This step ensures that your work area is ready for the new paint application, providing a clean canvas for your project.
By following these steps and taking the time to properly scrape and sand the surface, you'll create the ideal base for your new paint application, ensuring a polished and long-lasting finish.
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Use a primer to cover the old colour
If you're looking to paint over pre-painted surfaces, one of the most important steps is to prepare the surface. This can be done by testing the adhesion of the existing paint. Cut a small 'X' through the paint with a blade, cover it with tape, then rip off the tape. If the paint comes off, it needs to be removed or sanded down. If the paint is sound, you can proceed with priming.
Priming is an excellent way to cover old colours, especially if you're painting a bright colour over a darker shade, which would otherwise require multiple coats of paint. Primer paint is less expensive than regular paint, so using it as a base coat will save you money and ensure that you only need one or two coats of your new paint colour.
Primer is usually clear or white. If it's white, a light colour shouldn't be a problem, and a dark colour should also be able to cover it. However, if you're concerned about the primer showing through, you can get both the paint and primer tinted to the same colour, guaranteeing a perfect match and coverage in just one coat of each.
If the surface is smooth, clean, and the paint type is the same as what you plan to use, you may not need a primer. However, if there are any holes or imperfections, a primer will help to mask them and create a smooth, consistent base layer for your new paint.
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Apply a gloss or matte medium to protect the paint
When applying a gloss or matte medium to protect the paint on pre-painted figures, there are several steps to follow and considerations to keep in mind. Firstly, it is essential to determine the type of paint and surface you are working with, as different surfaces and paints have specific requirements. For instance, if you are dealing with a wooden surface, it is recommended to use a specialist wood primer to ensure proper adhesion and durability.
Before applying any medium, it is crucial to prepare the surface thoroughly. This involves cleaning the surface to remove any grease, dust, or dirt that may interfere with the adhesion of the medium. Sugar soap is often recommended for this purpose, as it effectively cleans and prepares the surface for painting. After cleaning, ensure that the surface is completely dry before proceeding to the next step.
If the surface requires sanding, use fine-grit sandpaper to lightly roughen the surface. Sanding helps create a slightly textured surface that enhances the adhesion of the medium. However, be cautious not to over-sand, as it can damage the underlying paint or surface. Once the sanding is complete, remove any dust or debris generated during the process.
Now, you can choose the appropriate gloss or matte medium for your project. There are various options available, including gels, sprays, and traditional brush-on mediums. Golden Artist Colors offer a range of products, such as their Soft Gel Gloss and Matte Medium, which can be used for sealing and collage techniques. Their Gloss Medium is also recommended for preventing discolouration and can be applied directly to the support.
When applying the medium, always follow the manufacturer's instructions. In general, it is advisable to test the medium on a small area first to ensure compatibility and achieve the desired results. Apply the medium in thin, even coats, allowing adequate drying time between coats. For added protection, consider applying multiple coats of the medium, following the specific guidelines provided by the manufacturer.
By following these steps and choosing the right gloss or matte medium, you can effectively protect the paint on pre-painted figures without the need for stripping. Remember to consider the unique characteristics of your project and adapt the process as needed to achieve the best results.
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Paint over with thicker paint or pastel
Painting over pre-painted figures without stripping the existing paint can be achieved by using thicker paint or pastel. Here is a guide to help you through the process:
Prepare the Surface
If you are working on a smooth surface, you may encounter issues with the new paint adhering properly. Consider using a flow medium, such as an acrylic flow release, to increase the flow consistency of your paint while maintaining a solid paint film. This will result in a more liquid-like consistency, allowing the paint to soak into the surface rather than beading.
Choose the Right Paint
Select a thicker paint, such as impasto acrylic, for better coverage and adhesion. Impasto acrylics have a higher viscosity, creating a textured appearance and ensuring the previous paint layer is adequately covered.
Apply the Paint
Once you have your thicker paint, you can start painting over the pre-painted areas. Take your time and apply the paint evenly, ensuring complete coverage.
Using Pastels
If you prefer to use pastels, opt for soft pastels, which can be applied over acrylic paint. Start by sketching your desired design with a graphite pencil, then lay down the main areas of color. Use a light touch at first, blocking in shapes and forms. Once you are satisfied with the layout, go over it with harder and more definite lines.
Blending and Details
Pastels allow for blending and adding fine details. Use your fingers, dampened color shapers, or sharpened blenders to blend colors and create smooth transitions. For fine details, use a blender's tip to pick up small amounts of pastel and apply them to the desired areas.
Fixing the Pastel
Pastels do not dry completely, but they will harden over time. To seal your work and prevent smudging, use a fixative or hairspray. Allow the painting to harden for a day or two before adding any final touches or lines.
Remember, when using pastels, choose the appropriate pastel paper, which is usually rougher than paper used for other mediums. Additionally, if the pastel does not adhere well, you can apply an acrylic medium, such as an acrylic pastel ground, to create a better surface for the pastel to grip.
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Frequently asked questions
To determine if the existing paint needs to be stripped, cut a small 'X' through it with a sharp blade. Press sticky tape over the cut and then rip it off. If the paint comes off, it should be removed.
If the existing paint is latex and you want to use oil-based paint, you will need to use a primer. The primer will act as a middleman, allowing the new paint to bond to the surface properly.
Covering a dark paint color with a lighter one will require multiple coats of new paint. To save time and money, you can use a primer to cover the old color before applying the new paint.
If you've diluted the paint with water, it will be easy to paint over the surface with thicker paint. If the new paint doesn't stick, you can add an acrylic medium such as an 'acrylic pastel ground' to provide a surface for the new paint to adhere to.
