Carbon-14 dating of lime mortar is a relatively new method to date buildings where no suitable organic material (construction timber, charcoal in the mortar, etc.) is present. In summary we estimate that, based purely on the measuring uncertainty in the C-14 determination itself, that the mean age of the Newport Tower samples yields a calendar age of AD 1665 calibrated by intercept with the calibration curve.
"Appendix: Carbon-14 dating of the Newport Tower,"
Newport History: Vol. 68
, Article 3.
Available at: http://digitalcommons.salve.edu/newporthistory/vol68/iss235/3