How To Paint steel, Aluminum, Plastic, and Acrylic

Detailed How To – Aaron McBride

This guide will cover prepping and painting of steel, aluminum, plastic, and acrylic plus more. I’m sure some people will think some of the steps are not necessary and quite extensive compared to some guides. Yes, this may be true but I am writing this guide to help get a quality finish from your case, not something that looks like the neighbor painted in his homemade cardboard paint booth with a 99 cent can of paint from the dollar store.

Before getting to the main parts I will sum up a few questions that are typically asked as well as general items will be needed. If there is any questions/something isn’t every clear feel free to email me with questions. I tried to make everything as simple and quick as possible so there might be a few grey areas for some people.

A few general items that will be needed when painting are listed below. All of this can be had quite cheaply from an everyday “dollar store”:

  1. Masking tape, ¾” being most common
  2. Razor blades
  3. Sanding block (not using a block will cause sand scratches in the final finish)
  4. 600, 800, 100, 1500, 2000 grit sand paper
  5. Scotchbrite pad
  6. Wax & grease remover OR Dawn dishwashing soap & highest content isopropyl alcohol you can find (typically 90%); this will be referred to as “item 6” throughout this guide
  7. Paper towels
  8. Rubbing compound & wax
  9. Although not necessary, masking paper will make things easier; newspaper is not recommended in the automotive industry although I have personally used it as well as Christmas wrapping paper for my personal work and have not had any issues

Below are a few common questions as well as the answers:

1. What is the difference between regular primer and etch/self etching primer?

Answer: A regular primer is made to go on the substrate and provide mechanical adhesion. This is done by the primer settling into the scratches created by scuffing or sanding. As the primer dries it shrinks causing the primer to grab onto the scratches providing you with a mechanical adhesion.

An etch primer is made to be put on bare metal and provides chemical adhesion as well as mechanical. The mechanical adhesion of an etch primer works just the same as a regular primer mentioned above. The chemical adhesion is achieved by an acid contained in the primer. This acid will etch itself into the substrate.

2. Do I need Krylon Fusion to paint plastic?

Answer: Absolutely not. Even though the Krylon Fusion paint says it can be used without a primer it is still a good idea to use one so this stuff can pretty much be thrown out the window. In my opinion this paint isn’t too great anyways.

3. Do I need to sand my case down to bare metal to repaint it?

Answer: No, sanding the case down to bare metal will possibly end up meaning more work and money for you; especially if the case is aluminum.

Here are a few tips to keep in mind throughout the process:

  1. Use a sanding block. Sanding by holding the paper with your index, middle, ring ringer and thumb will cause sand scratches which will end up ruining the paint job as well as possibly causing variations in the metal. A sanding block can be made out of whatever you desire.

  2. Keep away from silicone products or grease/oil while doing the project. If you have naturally sweaty/greasy hands, it may be a good idea to wear rubber gloves or wash your hands periodically while working.

  3. Prepping is everything! If you do not take the time to prep the item before painting, you’re just going to have a mess of a job in the end.

  4. Patience is a must!

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Painting/Prepping steel and aluminum without going down to bare metal

So you’ve decided to leave the finish and go the easy way. This is only recommend if the current finish is original, due to the fact that the quality of another finish is unknown and if the current finish is not peeling/flaking/delaminating. Using a Scotchbrite pad or 600 grit sandpaper, you want to scuff the current finish until all the gloss is gone.

The finish should look dull/hazy/milky. Once done, clean with “item 6″. You are now ready to paint. Lay down 2-3 coats of the preferred color, letting the paint tack between coats and then let completely dry. If 2-3 coats are not enough to give sufficient hiding of the “old color”, continue with more coats. Once hiding is achieved, apply another just to be safe. Once dry you have two choices: Clear and cut/polish or cut/polish. There is a How-To for this farther down.

Painting & Prepping Bare Steel

Steel is the easiest of metals to paint. To begin the prepping, you will want to wipe the item you will be painting using “item 6″. This is done so no impurities are bushed into the metal while sanding.

Sand the item down to bare metal using desired grit sand paper. I prefer 80 – it’s coarse enough to remove the current finish and the sand scratches are fairly easy to remove. Once sanded down to bare metal using 80, bump up to 180 until all/most scratches from the 80 are removed; then repeat the processes using 400.

Once done with the sanding, clean using “item 6″; once dry, you’re ready for paint. Using an etch primer, spray a single light coat over the item being painted. You want a nice smooth coat that BARELY covers the metal.

Once the etch primer dries you want to lay down 2-3 thin light coats of a “regular primer”, letting the primer tack between coats. When it comes to the spray cans, the Duplicolor high-build primer seems to work great for this step – it will fill any minor scratches that may still be around from sanding, it lays down very smoothly and sands nicely for a spray can.

Once the primer is completely dry, wet sand using 600, once done with the 600, bump up to 800. The idea is to create the smoothest surface possible as well as remove any specs of dirt/dust/etc that may have gotten into the primer. After wet sanding, once again clean the item being painted with “item 6″.

From here you can now lay down the paint. Two to three coats are sufficient, allowing the paint to tack between coats. Then allow the paint to completely dry. Once dry, you have two choices: Clear and cut/polish or cut/polish. There is a How-To for this farther down.

Painting & Prepping Bare Aluminum

Aluminum is quite a picky metal compared to steel. If steel and aluminum are put together, galvanic corrosion will occur. Because of this, aluminum should be worked with in an area that will not allow it to be contaminated by steel. Aluminum also cannot be sanded with anything coarser than p80 grit due to impurities being imbedding to the metal. Lastly when painting bare aluminum, a metal conversion is need. Minus the above, painting aluminum is somewhat similar to steel.

Sand the item down to bare metal using desired grit sand paper. I prefer 80 – it’s coarse enough to remove the current finish and the sand scratches are fairly easy to remove. Once sanded down to bare metal using 80, bump up to 180 until all/most scratches from the 80 are removed, then repeat the processes using 400.

Next comes the interesting part about painting aluminum: A conversion coating needs to be applied to the aluminum. This is typically a liquid which is put into a spray bottle and sprayed onto the item being painted. Once sprayed on, it is allowed to sit and then washed off using water.

After the above steps are complete you’re ready for primer/paint. Lay down 2-3 thin light coats of “regular primer”, letting the primer tack between coats. When it comes to the spray cans, the Duplicolor high-build primer seems to work great for this step. It will fill any minor scratches that may still be around from sanding, it lays down very smoothly and sands nicely for a spray can.

Once the primer is completely dry, wet sand using 600; once done with the 600, bump up to 800.
The idea is to create the smoothest surface possible as well as remove any specs of dirt/dust/etc that may have gotten into the primer. After wet sanding, once again clean the item being painted with “item 6″. From here you can now lay down the paint. Two to three coats are sufficient allowing the paint to tack between coats.

Then allow the paint to completely dry. Once dry you have two choices: Clear and cut/polish or cut/polish. There is a How-To for this farther down.
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Painting & Prepping Plastic

Want to paint plastic but keep on hearing about the Krylon Fusion stuff? That’s not your only option and not the best at that. Below is a quick guide to painting plastic pieces:

Take the item being painted and clean well, using “item 6″. This is so impurities do not get imbedded into the plastic upon scuffing. Next scuff the item to be painted using a Scotchbrite pad or 600 grit paper. You’ll know you’re done when the item no longer has a gloss to it. The finish should look dull/hazy/grey.

Once again clean using “item 6″. Next you have two options: Lay down a thin light coat of plastic primer and wet sand using 800 grit paper once the primer is completely dry. Once finished sanding, clean again using “item 6″.

You’re now ready for paint; lay down 2-3 coats of the preferred color, letting the paint tack between coats and then let completely dry. If 2-3 coats are not enough to give sufficient hiding of the “old color”, continue with more coats. Once hiding is achieved apply another just to be safe. Once dry you have two choices: Clear and cut/polish or cut/polish. There is a How-To for this farther down.

Painting & Prepping Acrylic

Tired of that acrylic case? Or maybe you have an acrylic part that you need to paint to match your case, then this is for you. This stuff is pretty tricky. Up until the point when I decided to paint acrylic, I could not find any information about it on the forums and most information on the internet was quite vague. After running into a few problems and many hours of testing, below is the way that seems to work best:

I cannot stress how important the primer is. I used white plastic primer made by Rustoleum – this is what will make or break the project.

If you paint the acrylic without using primer and put so much as 4 coats on each side, you will still be able to see through the acrylic when held up to light and it’s possible it will have a cracked spider-webbed effect to it. The primer is VERY important. One thing you must keep in mind here is the primer is used as a cover, not just a coat to help adhere the paint, so you don’t need to use one coat and make it light as possible. Spray this stuff as you would anything else.

The first thing you want to do is take the piece of acrylic you’re going to paint and using the 400 grit sand paper, wet sand it all over. The whole piece should now be hard to see through. It will look hazy/milky/dull. After the sanding is done, wipe down the piece with isopropyl alcohol and let dry.

Once the alcohol dries, wash it off with a good mix of soapy water, rinse off VERY WELL then let dry. After it dries, prime the piece you want to paint front and back.

Give the piece 3-4 good coats of primer. After the primer is completely dry, wet sand it really well using 400 grit paper, moving up to 600 and then 800. If any of the primer sands through to the acrylic, put another coat of primer and repeat the sanding.

After you’re done sanding, wash it off with water to remove the dirty water and primer you sanded off. Once dry it should be VERY smooth. After the piece is dried it’s onto painting. Give the piece 3-5 decent coats of paint, letting it tack between coats; I highly recommend using Rustoleum or Duplicolor paint. From here it’s onto cut/polish or clear/polish, which is below.

Cut/Polish

I am going to put this in a way that will be easiest for the everyday person doing it at home. Using 1500 grit paper, wet sand the item that has been painted, moving up to 2000 grit. Frequently check the paper and have a constant flow of water or scratches may occur.

Once finished the item will have a dull looking finish – this is perfectly fine. Using some rubbing compound (I happen to like the 3M which can be bought at Wal-Mart for a few dollars), apply the compound following directions on the bottle. Repeat this process 2-3 times. Once finished with the rubbing compound, polish using whichever wax you prefer.

Clear/Polish

Once the item has been painted, apply clear directly over the paint, not sanding, no cleaning, etc. The best clear I have been able to find in a spray can has been the Duplicolor – most of the other ones I have tried seem to dry similar to a soft wax or just aren’t clear and don’t lie down very good.

As for how many coats, that is all up to you. Although the idea that more clear will give more shine is not true. After the clear has been applied and let dry, completely wet sand using 1200 grit moving up to 1500 and then 2000. Be sure to check the paper often and have a good flow of water where sanding – if not scratches may occur.

Once finished the item will have a dull looking finish – this is perfectly fine. Using some rubbing compound (I happen to like the 3M which can be bought at Wal-Mart for a few dollars), apply the compound following directions on the bottle. Repeat this process 2-3 times. Once finished with the rubbing compound, polish using whichever wax you prefer.

If you guys run into any problems such as dry spray, runs, fish eyes, pretty much anything you may have a question about or need help with feel free to email me.

I will not be held responsible for any damage done to any item in which you decide to paint.

Aaron McBride

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