Phenol-formaldehyde adhesives are in the wood industry most commonly used for bonding of structural wood composites where high strength and durability of the bond line is desired. Their curing is rather complicated due to the reactions that can occur simultaneously. Based on the acidity or alkalinity of added catalyst during the synthesis, these adhesives are divided into novolak and resol type of resins. In the study, the curing of different commercial resol type phenol-formaldehyde adhesives was analysed with differential scanning calorimetry (DSC). The influence of the addition of basic catalyst on the curing of the selected adhesive was examined, and a simulation of time required for the curing of the adhesive at isothermal conditions was also made. It was found that the curing processes of different adhesives varied. Because the examined phenol-formaldehyde adhesives were already optimised during the process of synthesis by means of optimal catalyst addition, the additional amount of catalyst into selected phenol-formaldehyde adhesive was unnecessary and has a negative impact on its curing.