Can I apply Water Based Helmsman® over the oil-based Helmsman® product or vice versa?
Yes. The two products can be applied over each other as long as the first has fully cured. Follow the directions for the product you are using. Be sure to apply each coat with only one product. Do not finish part of a surface with one topcoat and part with the other as this could result in a uneven appearance across the surface of the wood.