The present invention relates to a process for the conversion of lignite ash, especially ash from dry électrofiltrage, in construction materials. First a coarse fraction with a lower limit of grain size of about> 500 mum is mechanically separated, the remaining fraction with an upper limit of grain size of about <500 mum or the very fine fraction with a grain size of about <100 mum, which is mechanically separated from a fine fraction essentially containing silica sand, is uttilisée in brick, while the fine fraction is used for the production of materials requiring quartz sand. Where appropriate, is mechanically removed at least most of the coal particles, coke particles and wood contained in the fractions so used.