There is no need for a round trip once you've made landfall.

Portal back home, arrange a boat and go back to the Mistlands with Black metal. Take the Moder power if you're worried about head-wind. Take 2 iron bars if you haven't found any and you build a Stonecutter to build *and destroy* Black marble buildings.

Black marble is much, much stronger than stone. There's plenty of it, use it.