Ran out of levelling compound when fitting underfloor heating, what are my options?
Judging by this language in the instruction sheet...


Allow to set (approx. 4 hours).

Finish by levelling off with a further layer of SBR
modified Bostik Cempolatex One Pack.



I'd conclude that you may apply a second layer of the product without priming. Whether it's appropriate to modify the compound with Bostik Cementone SBR is unclear, but that seems to apply to thicker applications.