@Globalforester , this reaction type is normally from acetone/solvent cleaner still on/in the metal to be sprayed [alloy/s are much more porous than steel]. First trick is to allow good flash off time between degreaser/cleaner, primer and first coat. Second trick is to use light heat to warm up the area to be sprayed after degreaser/cleaner, promotes flash off. A heat gun on low-mid temp' works perfectly for this, passing the heat gun in slow sweeping motion. Also, you may have
- a chemical reaction between two different manufacturers product [primer and paint] - here, it's always worth buying primer/s and paints from same manufacturer where they in house test compatibility, i.e. U-Pol, Paintman.
- the paint type doesn't like the acid etch - here, a good zinc primer usually works.