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Corrosion problems on aluminum ambulance bodies

We are experiencing premature paint failure on modular aluminum ambulance bodies mounted on truck chassis. These bodies are all welded aluminum with lights and trim that is attached with stainless steel fasteners. The paint failure seems to be due to corrosion between the paint and the body. We are using all of the paint manufacturer's recommended methods of surface preparation and application. We are also using a paraffin based sealant at all fasteners. Does anyone have any experience with the use of sacrificial anodes to help eliminate this problem? Can anyone lead to a source for information on the use of sacrificial anodes on a similar application?

Thank you,

Jerry Black
- Madison, Alabama
2003

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Although you say you are following pretreatment requirements, you haven't said what you are doing. The pretreatment is probably not good enough. Sacrificial anodes is a hopeless approach because you need an ionic circuit (conductive water all the way from the anodes to the point that is corroding).

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

Hi. Your paint problems are coming from a range of problems.Aluminum should be prepped between 22 and 26 °C. The aluminum WILL react differently with your paint products at these temps; proper sanding is a must, nothing courser than 220 grit should ever be used on the surface proper sealer coats. Must be applied to the surfaces being painted ..... My strong suggestion to you is Dupont DTM epoxy primer sealer, "great stuff". The use of electrodes will help but only with proper measures taken. Ihave been working with aluminum for a number of years so you can take my word on it.

Jimmy Hipson
- Yarmouth N.S. CANADA
2006