With a view to replace synthetic foaming agents in the production of foam concrete, renewable and naturally available soapnut (SN) fruit has been studied as a foaming agent. Soapnut foaming solutions are prepared in two ways, viz., water soaking for 24 h without heating and with heating of soapnut pericap over a range of temperature (i.e.70 °C–90 °C). The foam generated from the above foaming solutions are studied for properties such as initial foam density and foam stability. However, the use of this foam from soapnut led to cement setting problem, which is caused by the compounds present in soapnut. The setting problem is resolved by using alum as an accelerator. The addition of alum resulted in the formation of additional ettringite and enabled the concrete to set, which is confirmed through powder XRD. The properties of foam concrete produced with water soaked SN with heating is noted to be marginally better compared to those of concrete prepared by water soaked SN without heating. The pore size and shape are analysed using an image analysis technique, which gives good correlations with density and strength of foam concrete. © 2017 Elsevier Ltd