Résumé : The influence of the activating solution composition on the stability and thermo-mechanical properties of geopolymers made from a Cameroonian volcanic ash is investigated. NaOH, KOH solutions and silicate solutions with low modulus were tested. The samples are cured at 90 C and the mechanical strength increases up to 21 days. With NaOH the strength development is faster, with a dry and wet compressive strength respectively around 40 MPa and 20 MPa at 21 days. The largest particles only act as reactive filler while smaller particles dissolve in the activating solution as seen by SEM. Pure volcanic ash and synthesized materials consisted of mostly X-ray amorphous material with some newly formed crystalline phases. KOH specimens were found to be thermally more stable, shrinking less than 3% after heating till 1000 C. The obtained results suggest the possible use of the synthesized materials for building applications and low temperature refractories up to 700-800 C. © 2013 Elsevier Ltd. All rights reserved.