The purpose of this study is to investigate DEF development in heat cured mortars made of recycled sand aggregate with sodium sulphate or gypsum plaster powder additions to stimulated DEF development. Ten different formulations have been studied for more than a year. DEF damage comparison between different mortars made of RCA sand and standardised siliceous sand is made with or without sulphate addition. Sodium sulphate was used in three formulations at 5% of total SO3 by cement weight, while gypsum plaster powder was used in four formulations with two different fineness (<0.1 mm and 0.1–2 mm) and contents (1.2% and 0.8% of sulphate content in sand) to simulate a scenario of recycled aggregate pollution by gypsum plaster during the demolition phase. Three other mortars were formulated without any addition to determine the impact of sulphate addition. Sodium sulphate was found to induce and amplify DEF. Gypsum plaster powder did not enhance damage and both mortars made of recycled sand with or without gypsum addition showed little differences concerning DEF expansion. RCA based mortars had lower DEF damage than siliceous reference sand based mortars. This result is explained by air entrainment effect of RCA sands and to a lesser extent by chemical differences between mortars made of recycled and siliceous sand. Hence, DEF damage should be further studied at sulphate and alkaline content far above the current standard limits for RCA based concretes.