A pre-requisite for good results in hot-dip galvanizing is clean steel surfaces. One should therefore try to keep the surfaces free of paint, grease, oil and tar. Impurities such as these cannot be removed by pickling and result in black, uncoated spots after galvanizing. Surface contaminations in the form of grease, oil, tar, paint and welding slag require removal by means of degreasing, sandblasting or grinding. Contamination may be difficult to detect. If it becomes apparent after galvanizing the article may need to be regalvanized, which increases costs. Laser or flame cutting heats the steel and produces surfaces that react differently when galvanized. The coating thickness may be lower than expected and the adherence to the steel surface may be poor. The cut surfaces should therefore be ground to remove the heat affected zone before galvanizing.