Double diffusive layers, formed by heating a linear stable solute gradient from one vertical side wall, undergo a merging process from their initial to final thickness. This process, excluding the initial and final states, is different in each of several almost identical experiments, and in this sense it is said to be chaotic. The variation of the layer thickness during this process is analyzed and a simple quantitative measure for the level of chaotic behavior is suggested and applied for two different sets of experiments. Each set consists of several almost identical experiments, and the two sets differ in the wall-temperature rise curve. The results for the two rise curves considered, namely, linear and exponential, show a higher level of chaotic behavior for the exponential curve. The influence of the heating rate on the thickness variation is also discussed.