a method of cementing a casing in a well drilled in the ground comprises injecting a liquid material comprising phenol - formol resin from the surface , wherein the resin is modified by means of a determined amount of furfuryl alcohol , and an amount of mineral filler unreactive towards the resin is added . the invention further relates to a thermosetting cementing material comprising phenol - formol resin . the resin is modified by means of an amount of furfuryl alcohol and comprises at least a proportion of an unreactive granular filler .