I have a stamped concrete patio that needs to be resealed. The contractor who did the original work has left the area so I don't know what kind of sealer to use or the best who to apply it. There are a few marks where the color has been scratched to the point where the color has been abrased off and the bare uncolored concrete is visible. Any ideas for fixing that? Other than pressure washing well and waiting for a sunny day (I live near Seattle) is there anything else I should do for surface prep?