I gave a 30' sailing yacht with a cast iron fin keel. It was blasted and treated with a rust inhibitor wire brushed and washed prior to being coated with Hempadur Multi-Strength 45751 (not sure the number is 100% correct.) I now need to repair a patch about 100mm diameter. I see you do a Hemadur 45143 in 5L which is far omre than I need and makes the little very expensive. Please can you help?