The clay based paint coating was prepared both on a wood and a flat of glass substrates in order to study the adhesion. The scratch test technique associated to the acoustic emission was used to determine adhesion although the critical load which was taken as adhesion measurement. The critical load, mode of coatings removal and acoustic signal are discussed. It is found that the combination of acoustic signal and microscopic observations can indicate whether failure occurs following a cohesive or an adhesive mode. It also found that the critical load is determined by the appears of periodic patterns, this result was found to be in agreement with those obtained by others authors.