This paper reports the construction of mixed tethered layers on silica substrates, in which the relative amounts of the two polymers can be controlled to the desired value. This is done by exploiting the three-regime kinetics found for tethered layer formation of single-polymer systems. Two end functionalized polymers, different either in molecular weight or in chemical structure, were tethered sequentially: the first polymer was tethered to the surface from solution to form a mushroom layer; then, after the slow second regime had started, the solution of the first polymer was replaced with a solution of the second polymer. The original expectation was that, because the surface already contained a mushroom layer, the second polymer would exhibit only the second and third regimes of tethering. However, the second polymer exhibited its own (rapid) first regime in addition to the expected second and third regimes. It was determined that the unexpected first regime exhibited by the second polymer originated in the size difference between the two polymers in the sequence.