The oil used in the final step will stain gelcoat. Cover or mask off anything the oil might come in contact with before completing this final step in the three step process. I did not cover the deck, so you get to see how the oil stains gelcoat. I tried soaking peroxide and bleach on different occasions but nothing will remove the stains. Aside from that completely avoidable issue, the results are amazing. My teak was completely grey and stained, but I managed to do all three steps in one day with a couple more applications of oil during the next week, and the wood looks like new.