Correct, epoxy esters are not real epoxies. Basically an alkyd with a hint of epoxy resin added. Not much better that a plain alkyd system and not a true epoxy either and should never be applied to an galvanized or concrete substrate.
just to clarify, we do the zinc, epoxy, urethane systems on bridge coating all of the time. even some polyurethanes can not be applied directly to zinc because of the type of oils used, this is why an epoxy tie coat or intermediate coat is sometimes specified.
saponification can happen with all types of coatings such as epoxy esters, linseed oil paints, alkyd esters and some PVA latex can be affected. some modified alkyds have been designed to resist saponification even when applied over zinc or hot concrete with a high pH level.
First remove the rust with sandblaster and then wash it with detergent.Then paint the roof and then coat it with corrosion resistant lubricant.This method has been shared by a roofing contractor a few months ago.I hope you will surely like this method.
Last edited by Wildbill7145; 01-24-2017 at 08:19 AM..
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1. first clean the roof 2. cover everything down below with old drop cloths especially if their is concrete , ospho will eat through it . 3. apply ospho to all rust 3. wait 3-4 days and sweep roof to remove any white residue 4. apply rustoleum heavy rust primer 5. coat with zinsser 123 primer 6. topcoat with elastomeric roof coating !