Thursday, January 3, 2008

Painting Interior Trim Panels

There are a few general things that we should remember as we proceed through this process:

  1. The preparation that you do will directly affect the quality of the finished project.

  2. The time that you spend on each step making sure that everything is correct will show in the finished project.

  3. Whenever sanding (whether it be at the beginning or between coats, you MUST clean the surface. For this reason I strongly recommend that you have lots of rubbing alcohol on hand before you start. If you run out, then stop what you are doing and get more. Any sanding dust will make your job harder as things progress and will likely affect the quality of the finished project.

  4. Take your time!

Step 1: Sanding

First decide, do you want to keep the texture in the panel you are painting, or do you want a smooth surface? If you want to keep the texture, skip to step number 3 If you want a smooth surface, you will want to start the preparation by sanding with medium grit sandpaper (I usually start with 150 grit) until most of the texture has been removed and you are starting to scratch the solid surface you are creating. At this point you will want to use a higher-grit sandpaper (Usually around 300 grit) until the surface is smooth to the touch and has a consistent flat (non-reflective) look and no obvious scratches. If you have small dings or scratches in the surface, now is the time to repair them.

Step 2: Repairing scratches and gouges

One of the best ways that I have found to repair scratches and gouges in plastic panels is actually superglue. Many people are surprised when I say this, but the fact is that superglue is made from cyanoacrylate, which is a chemical that will create a chemical bond between most plastics. This means that you won't just be filling the hole; you will be replacing the missing plastic with something that will become completely melded with the plastic of the panel. I recommend using the superglue gel since it is easier to work with due to it not dripping where it isn't wanted. Simply squeeze a little bit of the superglue gel into the gouge or scratch until it builds up a small dome and then use the remnants of the sandpaper that you used in prepping the rest of the surface until the mound of glue is level with the rest of the surface and you cannot find it when you close your eyes and run your finger along looking for it. Once all of the imperfections have been corrected in this way, we're ready to move onto the next step of preparation

Step 3: Cleaning

Cleaning the surface is probably one of the most important steps in ensuring that your paint will adhere properly and won't crack or peel. For cleaning I recommend using a lint-free towel soaked with rubbing alcohol. It is important that you use a lint free towel; otherwise you'll be leaving lint all over your carefully prepped surface. Make sure to clean every nook and cranny of the surface, and pay special attention to any sharp bends or crevices, as this is where dust from sanding as well as other contaminates will usually hide.

Step 4: Etching Primer

In this step you'll be using etching primer directly onto the prepped surface. Start out by laying down two thin, even coats of etching primer, holding the can 8-10? from the surface and moving in long, smooth passes. After you have the primer on, use some 220 grit sandpaper to lightly remove any texture remaining from the spraying process. If you rub through the primer on an outside edge or corner, you will need to re-prime that area, trying to overlap the surrounding area by between 3-5 inches and then lightly sand again. With this first sanding, use light pressure and don't remove too much material. Allow the painted object to dry completely before continuing (refer to the can for the drying times).

Step 5: Sandable Primer

Now it's time to use the sandable primer. It is recommended that you use a different shade of sandable primer than the etching primer so that you will know if you accidentally sand through to the previous layer. Now that the etching primer is down and the surface is smooth and evenly done, you will want to add three coats of sand able primer, allowing it to dry completely and then lightly sanding with 600 grit sandpaper after each coat. Your surface at this point should be very smooth and the color should be evenly distributed. Double check everything at this point to see if you have any remaining imperfections that need to be repaired, because after this we will be doing the color coat and it will be much harder to go back and repair a mistake. Most imperfections that are visible at this point will still be visible when the painting is done. It's better to spend the extra time now to fix things early, rather than finishing the project and then deciding that you have to redo the entire thing to fix the problem.

Step 6: Color Coat

When you start on your color coat, make sure that you have enough paint to complete the part that you are working on before-hand, because if you run out and have to get more, it could well be from a different lot and have a subtle difference in color. To give some perspective, I used four cans of color coat when doing a Saturn's center console, so if you have a number of parts that are all going to be done at the same time, you might want to consider seeing if you can get the paint color you want in a case, as sometimes you can work out a discount this way.

Now, on with spraying the color coat on your part. At this point you should have a very smooth, very clean surface to work with. If not, go back as far as you need to in order to correct this situation. Now we're ready to start painting. When adding your color coat, hold the can 8-10? from the surface and with the can straight upright. If you need to, move the surface, not the can. Use smooth, even strokes and use light coats, allowing the paint to slowly build up with each consecutive coat.

On the first coat or two don't even try to cover the entire surface, since if you do you will probably end up with drips or runs. As the coats pile up the finish will smooth out and cover the entire area, so this is a good time to use patience. After you have built up the paint (allowing to dry between coats) to the point where the entire surface is uniform, do two more coats in the same way you have been thus far and then use some 1000 grit sandpaper to smooth down the surface and lay down 3-5 more coats, allowing to dry between coats.

NOTE: If at some point you do end up with spatter, drips or runs, wait for that coat to dry and then lightly sand with 600 grit sandpaper until you cannot find that area with your finger if your eyes are closed. Then just proceed with the next coat and double check that you can't see or feel the imperfection anymore.

Depending on the paint you use (metallic, flat, textured) and the effect that you want to accomplish, you may or may not want to proceed with the next step. If you are using a flat color without texture then you probably will want to use the next step. If you are using crinkle paint or other textured paint then you probably will not want to go onto the next step. If you're using a metallic paint with flecks of metal and a bit of a textured or subtle 3d look, then you may or may not want to use the next step (you should try both on a hidden area to decide).

Step 7: Color coat sanding

If you do decide to proceed with this step, this is where a super high-gloss look will start to take form. After all of the paint layers have had sufficient time to dry (I'd recommend waiting 12-24 hours to be sure), you will want to start sanding the entire surface smoothly with 1000 grit sandpaper and making sure to go over every area evenly. After the sanding with the 1000 grit sandpaper, wipe down the entire area with some rubbing alcohol and re-sand with some 1500 grit sandpaper. At this point there should be a slightly dull look to the part you are working on, with no scratches visible. Now you'll want to use some rubbing compound over the entire piece.

Step 8: Rubbing Compound

I recommend using 3M Rubbing Compound for this step. For rubbing compound I recommend doing it by hand with a lint-free terry cloth towel and working at it until the entire area looks clean and smooth. Use some rubbing alcohol to clean the entire area and examine in various lights (sunlight, fluorescent and incandescent) to make sure that the finish is uniform and repeat if necessary. If it is not necessary to repeat, we can go on to the next step.

Step 9: Polishing/Glazing

For this step I recommend 3M Finish Restorer. While it isn't exactly a polish or a glaze, I have gotten the best results of everything I've tried using this stuff and swear by it. For this step I recommend using a 3-4? polishing pad attachment on an electric drill in order to get a deep, even polish over the entire part. Make sure that the item you are working on has been cleaned thoroughly with rubbing alcohol. Add a little bit of the 3M Finish Restorer to the polishing pad, and with small circular motions begin applying the chemical over the entire surface of the part, going back and forth over the same areas in a slightly larger circular motion. When done right this will make sure that the gloss on the item even and smooth. Now, because both this step and the previous step have involved the use of chemicals containing waxes that are typically used only for the finish coat, use some wax-stripper over the entire part, and then use car wash soap and water to thoroughly clean the surface and dry it with a lint-free towel or chamois before proceeding to the next step.

Step 10: Clear Coat

Now we're down to one of the most important steps. Take your time on this part and your finish will be smooth, even and free of imperfections. Wipe down the surface of the part with alcohol before starting with this step, even though you have just washed and dried the part and allow the alcohol to dry completely.

Just like with the color coat, make sure to use smooth, even strokes holding the can 8-10? from the surface being coated. Take caution however, since clear coat will develop runs and sags much easier than paint will because of how thin it is. Continue adding clear coat until the desired amount of gloss is present and the entire surface is even and let the object dry for 6-10 hours before continuing. If you do develop any runs or sags, you will need to sand the area down to the paint and repeat steps 8 and 9 before continuing on.

Step 11: Repeat Step 9

After the clear coat is evenly done and the level of gloss is to your satisfaction, you will need to go back and repeat step 9 until the entire surface is as smooth as glass.

Step 12: Waxing

Well, now that you have an exterior quality finish to the part that you have been working on, what can we do to protect it? Well, just like an exterior finish, we can protect this one with a wax coat. There is a wide range of waxes out there, and I'll leave the waxing up to you and the instructions on your wax's packaging.

Well, that's it, you're done. Now be careful when reinstalling the part, since even though it is a quality finish, if you bash it into something hard or scratch it across something, it will leave marks, just as it would on the exterior. For the most part any small scratches can be resolved by repeating steps 11 and 12, unless the scratch is through the clear coat or further. In order to protect the finish of the part, you can use the same treatments as you use on your car's exterior (wash and wax). For washing I would recommend using your car wash solution (mixed into the water already) in a spray bottle and spray down the parts and wipe clean. After that, use a damp towel and wipe again. Keep a good coat of wax on it also, as this will help to protect it from the sun?s heat and UV light.

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