So one of the legacies left to us by our previous builder is the unfinished sill which needs to take our large sliding doors. The concrete needs to be 280mm wide here (so wider than the concrete within the nudura block), and currently the nudura blocks stop approx 130mm short of the required level. I can attach a strip of PIR to the outside face of the block to screed to but I'm struggling to see how I can get the inner strip attached to the nudura blocks. I'm thinking I can use some long fixings to stab through the PIR and in to the Nudura block (see pic), but worried this won't hold back the approx 130mm deep concrete I need to pour. Any ideas?

Stick it in place with this.

 

https://www.toolden.co.uk/p/everbuild-evb5minpu3-lumberjack-5min-wood-adhesive-gel-310ml

 

Just make sure it is in the right place.

Set your doors on a strip of compact foam screwed down on to the concrete core with a dpc lapping over the top. Cut away the icf to the slab height, not the floor height.