Concrete pumping is often judged by slump, yet mixtures with equal slump may require different pump pressures. This review revisits the traditional “no slip” condition through the pipe-wall lubrication layer and distinguishes water slump from chemical slump. Water slump may promote transfer of mobile paste and fines to the wall, while admixture-driven chemical slump may provide internal workability without equivalent lubrication-layer renewal. The proposed framework connects chemistry, particle-size distribution, packing, water and admixture state to bulk rheology, wall transfer, lubrication-layer behavior, wall shear stress, and pumping pressure. The proposed wall-transfer relation requires experimental calibration to determine whether equal-slump mixtures have different pumping demands.