The delivery of plumbosolvency treatment over the period 1995 to 2004 saw non-compliance fall from 25 % to circa 3%. Similar improvements have been observed in the UK where treatment measures have been put in place . Expectations were that a small amount of further improvement would occur in the first few years after completion of the treatment programme due to operational fine-tuning. Surprisingly, it has been found that lead non-compliance has steadily fallen over the following twelve years and is now 90% lower than in 2004. This change points to the structure of the corrosion layer evolving over this long timeframe as there have only been marginal changes to treatment over this period.