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Waterproofing timber floor - bathroom #2

My bathroom floor is hardwood timber. When wet it can let water through to the kitchen below between the floorboards. It is timber that has been sanded and coated with three coats of polyurethane. The timber is the only thing between the floors (so timber floor in bathroom - timber ceiling in kitchen below). if it is possible to keep the character timber floor while making it more water resistant that would be my preference. However I know timber is not ideal for a bathroom so open to new ideas if needed including new flooring if neccessary. The area to be treated is about 4 square meters. See photos. Some boards are tight and some have gaps. Have attached a close up of one of the largest gaps between floorboards (about 2.5mm). Job will include resealing where floor meets wall. Thanks! Chris