Abstract We report the presence of Actinomycetes in degraded sandstone monuments, and on examination of 173 samples we identified Nocardia restricta as particularly prevalent. In our procedure, the extracted bacterial DNA was the template in polymerase chain reaction (PCR) experiments in order to amplify specific regions of the 16S rDNA. The fidelity of amplified fragment was confirmed by nested-PCR or restriction enzyme specific cutting. To confirm the specificity of the assay, the amplified fragments were cloned in a convenient plasmid vector, the sequence analysed and compared with the expected DNA genomic portion.