Cleaning exterior finished wood can be tricky and can go wrong quickly. Chemicals should never be used anywhere near finished wood only when preparation of new finish is needed. Bleach commonly used for exterior cleaning can fade the finish, leave spots and damage to the point that refinishing may be required. Water alone can begin to remove finish as illustrated in top picture. This may also lighten the finish. Imagine if the dropping spots from water alone in the top picture were not correctly removed and dried. All wood and finishes are not the same. Let us evaluate and give you our professional opinion before hiring just anyone.