Frost attack is a major cause of building stone decay whose mechanisms are not yet entirely understood. Direct accelerated frost tests were developed locally to match regional environmental conditions and there have been considerable difficulties correlating between the results of different national standards. The European Committee for Standardization (CEN) introduced a direct test in 2001, however little guidance for the interpretation of the test has been made available to date.
In this investigation, a trial was conducted to compare a direct accelerated frost test to indirect methods of stone durability assessment, for building stones of known historical performance. The frost test proved to be unsuitable for the assessment of porous limestone, with durable stones failing the test while less durable stones passed the test and modes of deterioration observed bore little relation to those seen on stone buildings. It was concluded that direct accelerated frost tests were unlikely to adequately reflect natural processes to accurately predict durability.
Certain indirect methods of stone durability assessment that investigated the pore properties of the stone were found to be a more reliable predictor of frost resistance. Petrographic examination was found to be of value in the determination of intrinsic rock properties and for observation of changes caused by frost action.