An innovative experimental method, based on the thermal stability of ettringite, is proposed and implemented to dissolve the crystalline products formed during Delayed Ettringite Formation (DEF). The tests are designed to empty all the pores that are filled by ettringite during their formation. By characterising the porous structure before and after the heat-based dissolution test (HBDT) via Mercury Intrusion Porosimetry (MIP), it is proved that the pores filled by ettringite during DEF in the pore size range between 4 and 30 nm are emptied and that the pore size distribution (PSD) in this range is reversed, approaching the initial state (i.e. before the degradation induced by DEF). This observation helps to confirm the location of ettringite formed during DEF.