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© December 25, 2005 

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Painting Steel: Tips and Tricks

Written by Lee Wright.   

An assortment of modern railroad equipment scratch built in 1/8 scale by Lee Wright (photo by Lee Wright).

When someone said. "Cleanliness was next to godliness" they could have been talking about painting steel. Steel will have varying amounts of dirt, grease and oil on and in it when it is new. Don't be fooled because it looks clean.

Here will follow a somewhat boring but factual method for cleaning and painting the " Wright" way.

Tools you will need are a steel brush or a wire wheel on a drill, some rags or paper towels and some green 409. I use 409 because over the years I have found that it works as good as anything. After the bottle is about half gone you can fill it back up with water and it still works. It dries fast, is non toxic, you can use it in the house and best of all, you can steal it from your wife's pantry.

Square tubing usually comes in 22 foot lengths. Or course It has to be cut in half unless you happen own a semi. Square tubing is probably the worst. If you purchase it from a steel warehouse better take along some gloves. If you have a nice shop, I would suggest you do the first round of cleaning outdoors.  I try to clean the whole thing before making it much smaller. Set it on some saw horses or something similar. Make sure you put on a face shield. The dirt and grease, not to mention the little steel wires that can come out of the wire wheels, are eye hazards. Clean the whole piece fairly good with the wire wheel. Next spray with the 409, use the stream setting for more pressure.  Keep spraying and wiping until you are exhausted or your towel comes back clean (that will probably not happen). Now get out your random orbital sander. If you don't own one, stop reading this and go down to Lowe's or the hardware store and purchase one. Put on an 80 or 120 grit disc and sand away. I have used both the aluminum oxide and the carbide. Sometimes one will work better than others, so just buy a big selection.

Now that you can see the product, re-clean with more 409 and wipe dry. Let the material dry for at least 4 or 5 hours. Moisture will stay in the steel for a long time after it looks dry. At this point you are basically ready to prime. Next comes cleaning the sheet metal. It usually is not that dirty. In a rare case I have had to get out the old Milwaukee belt sander and give it a good going over. You can't hurt the steel, the sander is not going to put a divot in it. It would be hard to clean a 4'x10' piece of steel, so I have the sheet metal shop cut it to the size I want or close to the finished size. Most of the time this metal will look clean but don't be fooled. Get out your rags and the 409 and give it a good going over on both sides. Once your parts are cut out but not bent or formed it is time for sanding. Us a fine disc on the orbital sander 220 grit or finer. Sand until the metal is shiny and has a uniform set of scratch marks. If you have welded on it, get out the wire wheel and wheel the black away. Back to the 409 and clean it again. Let it dry for at least 2 hours before priming.   Ok now after all that scrubbing you are almost ready to start priming. However, I almost forgot, make sure you have removed all the drill burrs and rough edges.

On to paint selection: I have worked with all kinds of paint and paint equipment so I am not telling you this because it is all that I know. This seems too simple but let me tell you what I have learned.

Go to Ace Hardware or Wal-Mart and purchase cans of Krylon ruddy brown primer and light grey primer. Also purchase Krylon paint if you can find a color that will work for you. The Ace paint is good but the blue spray fan nozzle will only work one or two times at best. The cans are tall and I usually have to end up throwing half of it away. The old simple sprayer on the Krylon cans works just fine.

If you have an area that is rough or needs just a little filling, use the Ruddy brown primer and put on about 4 to 6 coats waiting about 1 hour between coats. After the last coat let it set for 2 or 3 days before trying to sand or paint over it.   On areas that are clean and smooth use the light grey primer. Put on three good coats waiting about 1 hour between coats.

To back up just a little: Sometimes we will have some grinder marks or gaps. Make sure you fix these before priming. To fill a deep hole or seam use J-B weld. Do not use Bondo. Bondo will fall out in a couple of years. However if you have just a small scratch, use the Bondo glazing and spot putty. Put a dab on the plastic squeegee and wipe it over the spot. Don't go back over it-- let it set up. Re-sand and fill again if necessary. Use the random orbital or a rubber pad. Sanding it by hand will just remove it and you will be back where you started.

When everything above is complete you are ready for the final priming, I usually take as much if the car back apart as possible. Prime everything with the light grey primer. Why? Because if you are not using black paint some colors are not opaque. If part of the car is primed dark and the rest is primed grey and you paint the car yellow there will be a slight difference in color. On the final sanding, use very fine sandpaper 600 or finer. I don't wet sand. Water will get in small cracks and the spray can will blow them out on your paint job. Do this sanding by hand. Cut the sand paper into 4 pieces. Get a can of spray adhesive (steal it from your wife again) and spray it on the back of the sandpaper and fold it over. This will keep it from slipping. Sand lightly and feel with your hand for rough places. Just knock them off lightly. Any deep scratching at this stage will show up in the final paint job.

I try not to paint more than 4 or 5 square feet at one time with cans. You may have to paint one side at a time unless you really know what you are doing. Don't forget you will need good lighting--outside is best if possible. Ventilation is also important. I use a big window fan pointed away from the work. As final prep, I wipe the whole surface with a tack cloth and check it for any missed particles.

Now the fun part. I will put 2 or 3 new cans in my sink and soak them in hot water for about 10 minutes; shake the heck out of them. Put on your paint mask and walk up to the beast. Blast out 4 or 5 sprays onto an old box or something Make sure the nozzle is clear and working correctly.

Start by laying down a light coat from about 12" inches away. Just a good dusting. Remember to develop a technique of starting and stopping the spray at the beginning and end of every stroke just like using a spray gun.  Avoid holding down the nozzle and moving the can back and forth like most people do.  That will make the paint too heavy in the areas where you stop to change direction and you might get running.  Lift up on the button before you stop and press down after your arm begins to move in the other direction.  This will take a little practice and a bit of coordination.

After this first light coat, wait 2 or 3 minutes depending on how big this is. Go over it again in much the same way only at a 90 degree angle if you can (if you went left to right, go top to bottom). Look for corners or areas that are not receiving much paint. Go back and hit them again.

Wait about 3 or 4 minutes and come back for a coat that pretty much covers everything. You should be holding the can closer now, 10" or so.

Wait about 5 minutes this time unless the project is over 4 square feet. What we are trying to do is let the paint set so that it doesn't run, but not so dry that the last coat will just set on top of the previous coat. This is kind of a judgment call comes from experience.

The last coat is the important one. Lay on the final coat as thick as possible without running it. Watch in the light as you are spraying. Is the paint smoothing out or do you see overspray not being absorbed into the area you have just painted. Keep going back, starting and stopping your spray until you see a smooth surface.  Don't over do it. If you get in a panic, just stop. Wait for 10 or 15 minutes and if it still doesn't look good, give it another coat. Try to keep it wet all over at the same time.

Some other good reasons for using spray cans:

  1. They are easy to come by.

  2. The colors will be consistent

  3. There is no mixing.

  4. Temperature and humidity has lesser effect than auto paint.

  5. Much less equipment needed

  6. You can do it yourself.

  7. Most attractive is not having to clean the gun.

I hope I have covered most of the bases and answered a few questions.


More on metal prep.

On structural material like angle iron and channel, I use the belt sander where ever possible, random orbital sander, wire wheel and plain old sand paper by hand. Using a grinder will eat into the metal and leave grinding marks that are hard or impossible to get out. If you have a sand blaster that is one of the best tools too use. Follow up the sanding with the 409 and water. Prime as soon as the material is dry or it will rust again.  Ruddy brown primer is best for this.

On rusted sheet metal 18 gauge or lighter. Throw it away and get new is the best advise. You will never sand deep enough to get rid of the pitting and it will show back up later.


Written by Lee Wright.   


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