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Andrew, Extend is not promoted to dissolve rust. It is not a rust "remover" but is called a rust "treatment". It is a liquid about the consistency of regular paint. It goes on as a milky color and turns black after drying. Two coats dry to a hard, black film. The pretreatment called for is degreasing and removal of loose rust by wirebrushing. I used it last year on one of my trucks that I painted. The cowling area in the engine compartment and the exterior roof had significant, heavy rust areas. Sandblasting in both areas was not feasible for me. In both cases light sanding with 80 grit paper was used instead of wire brushing prior to applying two coats of Extend. After scuffing up the Extend with 220 grit paper, I put on two coats of primer surfacer, sanded with 320 grit paper and then applyed two coats of acrylic urethane topcoat. Everything seemed to work out well except if I had it to do over again, I would have sprayed the Extend instead of brushing it on. Extend dries fairly fast and does not flow out well. That left very noticeable brush strokes in the dried film. That was not objectionable in the engine compartment but was on the roof. More sanding than should have been necessary was therefore needed. I do not have any long term experience with Extend so I can't verify how it is going to hold up, say over five years. I do plan on using it on one of my very rusty tractors as an alternative to bright metal sandblasting. For a technical data sheet on Extend, go to the link. Rod
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