Structural floor systems made of Timber-Concrete Composites (TCC) slabs are becoming more and more popular in office and residential buildings as well as in systems used for the renovation of old ceilings. Timber elements can be constructed as beams or solid slabs (massive CLT). Regardless of the main structural layout, individual components require using interlayer connections, which provide composite action in cross-sections. The most used connection types for TCC are mechanical fasteners, grooved or notched connections, and bonded shear joints. Bonded connections with rigid thin-layer adhesives provide high load capacity, but they are characterized by brittle failure due to their low ductility and introduced stress concentrations. An innovative flexible adhesive joint that ensures the transfer of high loads and high deformations simultaneously is presented in the paper. This connecting structural element, named PolyUrethane Flexible Joint (PUFJ) was examined experimentally in double shear lap tests of connections formed between two external CLT slabs of dimension 120 × 350 × 400 mm3 and a central concrete slab of dimension 100 × 250 × 400 mm3. Shear connections between the composite elements were made of a two-component polyurethane PS type adhesive layer of thickness 3 mm. The tested specimens were prepared in two variants of the application: wet application in the form of liquid adhesive and dry application in the form of prefabricated polyurethane layer glued to the elements by thin polyurethane adhesive. The effect of the adhesive application method on the stiffness and capacity of the TCC joint was investigated. In the paper, the analysis of the experimental tests’ results is presented.