I'm putting in a wc downstairs and ordered 8 lengths of 3x2 from beatsons ...the order came today and instead of 3x2 it's 2x5 .....the guy says that it's clear and is standard for building partitions....but it looks a bit thin to me....is this suitable for building a partition wall and putting in a door frame.....I also have 12.5mm plaster board.....total width with the plaster board is 75mm