We've started to pour our below-ground ICF (Nudura) and the builder is using a martar waterproofer, on the container it says not to use in structural concrete or concrete containing rebar - both of which ours is. Builder says "everyone does it, mate" - but, as ever, I'm worrying. Should I be?

If the additive is not approved for this, why is he using it?  I thought that normally you would get readymix for ICF, not site batched.

We're mixing the first few courses by hand (albeit in a tub mixer) because of various things.

As above, plus why use in in concrete that will be encased? Great for render or patch repairs in a concrete slab but I can’t see any benefit in ICF

I guess because the ICF forms are not waterproof, and the poured concrete in the middle is continuous with the foundations, no damp proof membrane?

Our polystyrene ICF has a waterproof concrete raft below it with Sika additive. There is a waterbar set into the raft just after pouring where the ICF goes and the first pour of concrete also had a Sika waterproof additive. Part of our ICF is to be backfilled as we are building into a slope. This wall however is being clad in blockwork and slurry tanked prior to the back fill.