filling aquaboard, cement board etc

[DeadBeat]

im getting toward the point of sealing my aquaboard panels on my bathroom wall. Ive built a niche into the wall in the shower area so i want it to be extra water tight, to do this, ive bought some tanking membrane to paint over all the corners and joins, however..

what do i use to seal any gaps between the cementboards, ill then go over the gaps with the tanking tape and then tanking membrane, but i feel there should be a seal underneath this in the gaps. the gaps are mostly very small but the odd place there might be up to 5mm

thanks

 

[Flyboytim]

Use a gap-filling polyurethane adhesive/sealant such as Mega Strength Adhesive from TileGiant (NoMorePly board recommended) or equivalent product.