Your project is hopeless, without a thorough cleaning of the surface, galvanizing is not possible. Practically all coating processes are very sensitive to contamination, but the processes where a metallurgical bond is created between the layer and the substrate do not tolerate any contamination at all. The residues of organic substances (oil, grease, paint residues and others), which form a charred separating layer on the substrate surface, are particularly bad. Precisely for this reason, the surface preparation before galvanizing (sandblasting, degreasing, etching and other processes) is crucial for the result of the coating.