A couple of years ago while living in Mexico I played American Football. Because we did not have all the sports stores that are available in the United States, we had to make due with second hand equipment. Our team colors were blue, orange and white, but the helmet I was able to buy was yellow. I had to figure out a way to get the helmet ready for our first game.
Ideally you want to buy a new helmet if you can. But if there is no way to purchase one you can make an old helmet look new. Be sure to inspect the helmet as much as you can before deciding to use an older one. The helmet is designed to protect your head while playing. It does no good to play with a faulty helmet.
Before you start painting your helmet you want to take the necessary precautions to get a good final product. Consideration should be given to your safety in the process. Plan to paint in a well ventilated area. This could be outside, but you also want to guard against high humidity and dirt getting into your work. Fortunately a helmet is small enough that you won't be breathing the paint fumes for hours. If at all possible use a paint respirator to protect your lungs. If this is a one time job, it may not be that necessary. But if you ever plan to do much painting, a respirator is a must have tool.
I started by removing all of the padding from inside the helmet. Most of the pads were held in by Velcro hook and loop fasteners as well as snaps. These were all easy to remove with just a little bit of work.
Remove the face mask by removing the screws holding it in place. This was easier than I thought it would be. I did not paint the face mask. Mine was coated with a rubberized coating that you would probably have to remove and reapply with a dipping process.
Clean and Sand the Football Helmet
Once you get the face mask and the padding removed, remove all the decals. If you want to save some of the original decals you have the choice of pulling them off carefully so as to reapply them, or you can mask them off with tape and paint around them. Masking them off can be difficult. You also may have problems if the decal is clear and shows the original paint color.
If your helmet already has a nice paint job and you are just changing the color you can use a Scotch-Brite pad to sand it. This is rough enough to knock the shine off the current paint job and allow the new paint to adhere to it. The paint will not properly stick to any part of the current paint job that has a shine to it.
If the helmet has been used and needs some extra help smoothing it out, you will need to graduate to a full sanding process. If you sand too much then you risk weakening the integrity of the helmet. Start with a medium paper in the 200 grit range. You may need to go coarser (a smaller number) if you have some extra tough sections. Eventually you want to work your way up to a 400 grit wet sandpaper to do the final preparation.
Warning: At this point you are ready to put primer on the helmet. If you touch it with your bare hands you risk transferring oil to the helmet and creating a spot where the primer and paint will not adhere. If you do have to touch the helmet you need to clean it again. It is best to have some way to hold the helmet or suspend it on a stand so you no longer have to touch it.
Prime and Paint
I used spray paint in a can that I bought at the local discount store. You want to hit it with primer first and let it dry. Do another light sanding. You should apply at least 2 coats of primer. If you have time to do 4 coats it will be much better. The primer helps fill in the small blemishes as well as gives the paint a good base.
After each coat of primer or paint you need to do a light sanding and clean the surface with a tack cloth. Of course, you will not sand after the final coat of paint.
Following the instructions on your paint and primer for drying time, you want to start shooting the color onto the helmet. Read carefully on the paint can to know how much time you need to leave between coats. If you let the paint dry too much between coats you will have to allow it to cure at least 24 hours before prepping for the next coat. That is only necessary if you miss the window of when you are supposed to start applying the following coat.
Paint Can Technique
You want to be in a controlled environment when you paint. Meaning that you don't want dust and wind blowing around while trying to apply the paint. But be careful to work in a well ventilated area.
While painting you must keep the can moving. Don't worry about getting a good thick coat the first time. Many thin coats will look much better in the end than a couple of thick ones. With thick coats you risk causing the paint to run which will be noticeable in the final product unless you take the time to really sand it out again. You should paint at least 4 coats of paint, and more if you have time.
Allow the helmet to dry according to the paint manufacturer's suggestions. If you can put the helmet in a controlled atmosphere it will dry more quickly. For example, if you live in a humid environment you will do better by bringing the helmet into a part of the house that has air conditioning. However, you don't want paint fumes all over the house. If you have a garage that you can store the helmet in until most of the smell is gone, you will want to do that. Then you can bring it inside for a final curing time.