Ask the Expert Question-and-Answer Archive

by Ron Joseph

September, 2003

Painting Aluminum Boat

Q. I am interested in painting our aluminum boat. It has been stripped to bare metal. I would like to know the steps that I need to follow and suggestions on the primer and paint to use. The boat is a freshwater craft. I will be painting both the interior and above waterline exterior. I also would like to know if a high volume low pressure sprayer would be a worthwhile investment for this project (I have the air compressor).

A. Aluminum is a very difficult substrate to paint successfully. In professional circles companies go to great lengths to prepare aluminum before painting because paints and coatings do not adhere easily to the surface. Ideally, you should take to boat to a local custom coater (job shop) to have it prepared properly using a conversion coating. If you do not want to do that you are left with having to do a second class job and hope that the paints adhere (stick) as best as possible. Please be warned that my suggestions below are not guaranteed to work. I am only offering these suggestions in the hope that you will get by. If you don't want to take the risk of spending weeks or months redoing the paint job only to find that the paint comes off, then I suggest you take the boat to a professional who can perform at least the surface preparation for you.

Thoroughly sand clean and wash the aluminum surfaces. Be sure that there are no contaminants left behind by the stripping process. Purchase an acid etch "wash primer" from an industrial paint store and ask the folks there for directions to apply the wash primer to aluminum. The instructions are different for aluminum than for steel. If the folks at the paint store don't know the difference then call the paint company and get directions from the technical folks there.

A good high quality "marine" grade two component epoxy primer is in order. After you spray apply the primer, and allow it to dry then you may spray apply a two component polyurethane top coat paint. Be sure to check with the paint supplier to ensure compatibility between the epoxy primer and the polyurethane top coat. Be sure that you are in an enclosed area with good ventilation before you proceed. A high quality HVLP spray gun will do the job well. These spray guns are not inexpensive, so be sure that you will have other jobs to perform that will require the use of a good spray gun. Be sure to select a gun that will matched to your compressor an HVLP gun will drain the air from an average home compressor very quickly and the gun will not perform as expected. Know the specifications of your air compressor such as CFM (cubic feet) of air. Bring this information with you when shopping for HVLP spray gun. The spray gun will require enough CFM to perform at is highest level of quality. Do not select a spray gun that requires greater CFM than four compressor can supply.

This type of system requires expert knowledge and handling. Please be aware that coatings and solvents are chemicals and therefore you should always pay attention to proper handling procedures and be prepared to wear protective clothing, such as respirators, gloves, coveralls, etc. For further information on the health and safety requirements for the coatings and solvents you wish to use we strongly advised you to contact your local coating supplier. If possible, go the extra step and look for this information on the website of the product vendor.