Hi Joshu, brachiopod is right: they do use caustic soda to strip doors. We had one stripped years ago, but my husband has done it himself since. Whenever he's finished stripping, my husband scrubs the wood with a mild detergent solution (Fairy liquid or something) and then rinses thoroughly several times with cold water and we've never had any problem with white marks. Perhaps it wasn't rinsed properly at the place you had it done. Also, as caustic soda really dries wood out, we've also applied linseed oil to the doors before using anything else, to help 'moisturise' the wood. Hope this helps, good luck.