This invention relates to aqueous acidic solutions which are thickened by cationic polymer, the polymer being added to the solution in the form of particles below 10 .mu.m in size. The useful cationic polymers are formed from a water soluble cationic ethylenically unsaturated monomer or blend of monomers comprising dialkylaminoalkylacrylics that includes a polyethylenically unsaturated cross-linking agent. A peak viscosity is achieved in the aqueous acidic solution at a particular cross-linker concentration.
The concentration of cross-linking agent chosen is carefully controlled so that the viscosifying effect can be optimised whilst minimising the amount of polymer that has to be added. The amount of polymer in the aqueous acidic solution is typically in the range of from, 0.01% to 5% dry weight polymer.