Why is the primer coming off after I peel the finish coat back?

Fellow NOMMA Members came to the rescue (by way of using NOMMA's ListServ) and offered the following suggestions:

Although I am not an expert on the matter, the rule of thumb in metal coating is that you can use water-based top coat over an oil-based primer, but not the other way around. This is not true however for wood and some porous materials, but there we have specifics about the times in between applications (each product has its own set of rules). There are very good water base primers and top coats for metal today, and the technology keeps improving day after day. I personally use a Tnemec product. The water-based paints have the great advantage of offering the VOC compliance required by most states, are definitely more environment friendly, with a very low toxicity for the user.
- Philippe Fiers, Armadillo Metalworks, Inc.

The fact that the lack of adhesion occurred at a joint in the tube, does that not at least leave open the possibility of a pin hole leak? It does not take much of a pin hole at all for moisture to find a way. Once the moisture has broken the bond between the primer and metal, it's a matter of time before it creeps along and breaks that bond a little at a time. Which would explain why it took 2 years to notice it. The moisture can come from condensation inside the tube. I've seen that effect in TS pickets before.
- Tom Duello, Hemi Systems

We used to wipe down with lacquer thinner and occasionally had issues with the primer not wanting to adhere. Our paint supplier suggested that we change to wax and grease remover, which is very common in the automotive paint industry. So now we wipe with wax and grease remover after fabrication and then abrasive blast, followed by epoxy primer and two coats of acrylic urethane enamel. Everything seems to stick pretty good now.
- Dan Donovan, Allform Welding Inc.

We had problems with any petroleum based thinners used to clean before paint.They all leave a residue. So we went with just soap and water. It’s actually a cleaner/degreaser for cleaning commercial kitchens. Works very well...is a lot cheaper than thinner...$25.00 for a 5 gal. bucket and rinses off clean. In the summer out here it dries in 10 minutes for paint. In the cooler weather we go over the pieces with a weed burner torch to dry them off and warm them up.
- John McLellan, McLellan Blacksmithing

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