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Rubbing Out Paint

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Old 05-16-2012, 05:57 AM   #1
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Rubbing Out Paint

"The hardest part for some car modelers is getting a gloss finish on their models. There are some that can get an excellent finish right out of the spray can or airbrush. I am not one of those so I have to rely on having to rub out the pain to get a nice finish.


BE WARNED THAT THIS PROCESS IS NOT EASY OR QUICK. There are still times when I screw up this process, so don't expect great results every time.


ITEMS NEEDED
  • Sandpaper of various grits 600-20,000
  • Polishing Cloth
  • Polishing Compound
  • Water


(Note that I did not say you needed a polishing kit. You can get a polishing kit and this is a good start, but you can get the components needed from other sources.)


SANDPAPER

The polishing kits have grits ranging from 1000-20,000. Personally I never use a grit finer than 3000 and have had very good result. This does save on a bit of time and I don't really see the need to go any higher. For sandpaper you can go to your hobby shop and get the sandpaper needed. Another (cheaper) source can be a hardware store or an auto body shop. Make sure the sandpaper is the wet/ dry type.


POLISHING CLOTH

The polishing cloth that comes with the Millennium 2000 polishing kit is very good and you can buy this cloth separately from a hobby store. Any cotton cloth will do. I have bought a polishing cloth at a hardware store for $2. Even an old T-shirt will work. Be careful that some cloths will actually scratch your paint job when you rub it against the paint. Paper towel can do this.


POLISHING COMPOUND

This is the final stuff used to get your finish that amazing shine. There are a variety of compounds to use. I have tried almost everything under the sun to find the best polishing compound. (Millennium 2000 Polishing Compound, Vim, Brasso, Silvo, Tamiya polishing Compound, toothpaste, Liquid Glass Pre-Cleaner, Automotive Wax, Plastic polish, The Model Treatment, Duragloss Precleaner, etc.).

From this I have found out that different polishing compounds work differently on different paints. One that might work beautifully on one manufacturer's paint may even dull another’s. Tamiya polishing compound work best on the Tamiya paints.

The best polishing compound I have found for most paints are the Model Treatment Wax, Liquid Glass and Duragloss Pre-cleaners. These seem to fill in minor scratches and give mirror like finishes. Always test your paints and polishing compounds on scrap bodies.

The paints that seem to work well are lacquer paints. These dry relatively quickly and hard. I always make sure the paint jobs have had plenty of time to completely dry. I even have a food dehydrator to help dry some paint jobs


THE POLISHING PROCESS

The reason you want to rub out a finish is that your finish is rough from the painting process. Some people call this orange peel since it is so rough it looks like the skin of an orange.

Here is an exaggerated cross section of a model finish with the bottom layer being the plastic. The middle layer is the primer while the red is the paint job. What you are going to try and do is to sand away the hills until the paint is completely flat:




Wet the area you will be sanding with water. This will help with the sanding process. It will keep the sandpaper from getting clogged. When sandpaper is clogged you can create deep scratches that are hard to get out:




If the paint job is rough I usually start with[piece of] 600 grit sandpaper. If I happen to have a very nice paint job I can start with 1000 or 1500 grit sandpaper. Start sanding a small area in a circular motion. DO NOT APPLY A LOT OF PRESSURE. If you apply too much pressure you can cause scratches. I personally use my fingers and sand in circles. Others swear by the sanding block and straight motion with the sandpaper. The sanding block is supposed to even the pressure on your model and not cause hills and valleys during sanding. This might be recommended if you are first starting off. I find it cumbersome and not as flexible as I want.

I have also tried the straight sanding motion. The idea is you sand straight in one way then rotate and sand another way for a while. I haven't found this method very successful:




The idea is to sand the paint to just before you are completely flat (still some valleys). Here is where experience comes in. What I do is sand with the 600 grit for a few minutes. I then dry the area with a paper towel. The top areas will be flat while the valleys will still be somewhat shiny. Do not sand until it is completely flat. If you do so, you may go too far.

If it is still quite bumpy then add some water and start sanding again. Keep repeating this process until you think you are ready to go to a higher grit sandpaper. If you change to a higher grit sandpaper too soon then you will notice that your progress will be very slow with the higher grit. If this is so you can go back to the 600 grit sandpaper.

Every so often you should also check your sandpaper to make sure it isn't clogged up. Clogged up sandpaper won’t work as well and can cause scratches on your paint:




At this point I use some polishing compound and quickly rub it with the polishing cloth. The polishing compound does remove some paint so expect some color to appear on your polishing cloth:




By doing this you will get a relatively glossy surface and when you start sanding with the next higher grit you can easily see the new flat and gloss areas. You will also see the scratches that you are going to have to get rid of:




Start the sanding process as before by adding water and sanding lightly:




Always dry your surface and check your progress frequently. If you have to use the polishing compound then do so:




Eventually you will get to a point where the sanding is ended and you have to polish the paint. I have found that the harder you rub the nicer the paint job. Be careful with plastic kits that you don't apply pressure in the wrong place and break your model.

Die Cast cars are excellent for testing your skills because it is metal you can apply a lot of pressure and get really nice paint jobs. The polishing compounds I have noted before appear to fill in some minor scratches. It appears to be this reason that I don't have to go higher than 300 grit in the sandpaper:




TIPS


MORE PAINT ON HIGH SPOTS

Since there is a constant danger of rubbing through the paint you have to be aware of these areas and avoid applying too much pressure to these areas when sanding. To help yourself during the painting process you can add more paint to the higher areas. This is easier done with an airbrush than a spray can


Sample of a curved painted areas:




The tendency is to sand the area flat. This results in going through the paint to the primer, and maybe even going through to the plastic. Always be aware of this and do not apply too much pressure on the top:




PAINTING

During your painting process you can control which areas have smoother paint compared to others. This is usually due to over spray. Since it is easier to sand flat areas try and get the nooks and crannies of the model to have the smoother finish. This will make the sanding process much easier.


CLEAR COATS

A problem with sanding the paint job is the worry about going through the paint to the primer or even to the plastic. Some people try and solve this problem by putting a clear coat on the paint color. You then rub out the clear coat. When you start seeing color on your polishing cloth you know you have gone through the clear coat and should stop.


HARD TO REACH SPOTS

One of the worst things about rubbing out paints is trying to sand those hard to reach spots. To get to those spots I have tried various techniques, cutting up small strips of sandpaper, wrapping sandpaper onto a toothpick, handle of a paint brush, a cut down popsicle stick. You can also get sanding sticks and cut them to size for sanding.


Q-TIPS

During the polishing process there are also those hard to reach spots. One way to get to them is to use Q-Tips. These get dirty very quickly so make sure you change these very often.


OOPS!

If you do go through the paint to the primer sometimes you can repair this. (not always) With an airbrush you can try and spray only the area affected. Rub out this area and hope that the paint matches the surrounding area. The problem is the paint from the same bottle will have different hues. This is due to the humidity, amount of thinner, pigments etc. If you are lucky the repair job will blend in. If you are unlucky and the attempt at the fix looks terrible you are going to have to start over again and paint the entire body.


MULTIPLE COLOURS AND DECALS

For multiple colors you cannot rub out the paint the same way as with a model with one color. The rubbing out process actually takes off a thin layer of paint and there is a problem with carrying this paint to the second color. The only way around this is to add a clear coat. You can then rub out the clear coat.

Clear coating over decals is a personal preference. Some don't want to do it since real racecars aren't clear coated. I like to clear coat depending on the number of decals. Older racing cars had little to no decals so I generally don't clear coat here. These cars usually have just a number and sometimes a name. If the model has a lot of decals I will add a clear coat mainly to smooth out the overall shape.

Both of the above topics are related with the fact that they create bumps or steps in your paint job. The trick is to try and level these out. You have to put enough clear to cover the step so that when you do rub out the paint you even the step out.

Side profile of the plastic before painting:




First color is painted on:




For a two tone paint job here is the masking tape being applied:




In this situation the spray can is aimed the wrong way. This way the paint builds up on the edge of the masking tape:





Here after the tape is removed there is a raised edge that may produce a problem later on. This edge is hard to remove without contaminating the initial layer of paint:





Here is the preferred direction of aiming the paint spray. There is no buildup of the second color against the masking material:




Here is the paint job after the masking tape is removed. The first color of paint can be polished out but not the second. This situation can also represent a decal on your model:




Here a clear coat is applied to the two (2) paint colors or the decal:




Here is the step from the two (2) colors or from the decal. You can leave this as it is if it doesn't bother you or you can try and remove it:




If you try to polish out the bump now it is most likely that you will go through the clear and start damaging the second paint color or decal. If you go through the clear and hit the second color of paint it is possible to save the paint job by immediately spraying another clear coat. If you have rubber through to a decal it is most likely damaged beyond repair:




This is what you want to do. You want to add enough clear coats so than when you do rub out the paint (dotted line) you do not risk cutting through the clear coat and damaging the second paint or decal. This diagram is exaggerated and your model should not look like it has an inch of paint covering it. Too many layers of clear and you lose detail and panel lines. The total number of clear coats depends on the paint but generally I have 4-5 layers of clear. Something like Future floor wax needs something like 10-20 coats while a 2-part urethane needs 1-2 coats.

And here is the finished product all evened out:



CONCLUSION
You now have the basics for rubbing out paints. I believe I have covered everything. If there are any questions just e-mail me and I will try and help. The key words are patience and experience. After a while you will develop your own rubbing out process. Don't be afraid to try different methods. Something that didn't work for me may work well for you."
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Last edited by Superquad7; 05-17-2012 at 10:47 PM..
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