Although this is something that may differ from one situation to another, it is generally recommended that you have pressure washing done on your property at least once every two years and in some cases, on an annual basis. One of the factors that can help to extend the amount of time between pressure washing is the chemicals that are used during the process. Without some of those chemicals, a problem with mould and mildew is going to resurface very quickly but those chemicals help to keep the problem from becoming an issue for a very long time.