There was a inventor in Germany which got featured in a science show on television, which did something similar. He build a big pressure cooker where he placed the wood and a liquid mixture inside and let it cook for many hours. The wood got soak through completely, which gave it, as he claimed, resistance against rotting at every layer. For outdoor appliances the wood would not need any coating and not deteriorate. There was no mention about the hardness, but he also didn’t press it.