Formulation Effects on the Performance of Aluminized Epoxy Mastics
In an earlier paper1 one of the authors reviewed the use of aluminized epoxy mastics as overcoats for the protection of degraded steel surfaces bearing old oxidizing systems based on lead pigments. Coating systems based on such overcoating strategies, while broadly successful, have suffered on occasion from premature breakthrough corrosion of the rusted substrate at power cleaned areas, and from a dramatic and extensive sheeting delamination of the original aged lead and oil coating system from the steel where the epoxy mastic (and subsequently applied intermediate and/or finish coats) have been applied over the existing system. Such delaminations are not observed before recoating and are reasonably associated with the overcoating strategy.
The earlier paper identified three primary requirements for effective systems of this type: 1.) the coating should have high wetting properties in order to penetrate existing rust layers at power cleaned areas, 2.) it should efficiently inhibit the progress of corrosion at these same areas, and 3.) it should accommodate incurred stress accumulation without undergoing brittle failure (i.e., without failing adhesively or cohesively itself and/or without inducing similar failures in the pre-existing aged oxidizing coating system to which it is applied).