Member companies of the British Stone Federation answered a questionnaire on the reasons why they decided to clean a building (6 categories); on the benefits expected from cleaning a building (7 categories); and on the price range per square meter for six types of stone cleaning techniques excluding the cost of scaffolding. Results are given in table form. The question of how often a Portland stone building should be washed is also discussed, the answer depending mainly on the location of the building: from 5 to 10 years if in a major city, and every 60 years if in the country.