There are many ways to use hardiflex. One possibility is to cover the joints with a (ready available) kind of fabric and fill it up with epoxy. Mostly it will crac after some time. Another way is to make frames of aluminum L-profiles (along the wall) and T-profiles in the centre and lay down the hardiflex-tiles. The advantage is that you always can reach the space above the hardiflex ceiling. This is only possible if you have all the rooms downtairs.