Here is the rule of thumb for patching concrete. If the patch is 2 inches thick or more, use concrete mix, which is sold in bags at home centers and hardware stores. Concrete mix contains small stones to strengthen it. If the patch is less than 2 inches thick, use sand mix, which is also sold in bags but does not contain stones. Special patching cements, which are more expensive than concrete mix or sand mix, can also be used for thin or small patches.
Some special cements resist cracking even if spread very thinly.
Always read and carefully follow directions on the package for any patching material. Peeling gutters Peeling on painted gutters and downspouts can be caused by the substrate not being properly cleaned or primed prior to topcoating. If peeling occurs, scrape to bare metal. Make sure no trace of oil, grease, detergent film or moisture is present before priming non-ferrous metals with galvanized and aluminum primer. For ferrous metal, use a rust-stop primer.