Cement sheet gaps

Finishing off the bathroom floor and putting in cement sheet before putting down the vinyl.
Problem is as the room is not square we have a lot of gaps (1/4" or so) between the sheets, what is the best solution for filling these voids, I was going to use no more gaps but feel that it may be too soft, is there a render that would be more appropriate???
Thanks in advance and if anyone wants to come out and show how it's done you are most welcome:rolleyes:

You can get base coat for cement sheet, which is similar to what you would use to join plaster board. It sets really solid and is waterproof, you can use paper or mesh tape to reinforce it too, just like you would with plaster.

If its a floor that you intend to tile over, I'm not sure that it is worth the trouble ... do the gaps just go to another layer of floor below the sheets? If so I'd probably just use some solid gap filler.