Contracts or agreements with builders are not always properly written down or, in some cases, documented at all. In cases like this, dates when the works are to be completed are not always stipulated or agreed – or they get pushed back because of extra work or inclement weather.
So what happens when the builder fails to work diligently or even fails to appear on site? If there is no provision in the contract or agreement for an extension of time to the completion date, then the builder must be served with a notice stating why you think he is in delay and what date the works should be performed by BEFORE the contract can be terminated or before you employ alternative builders to take over. It is called "making time of the essence".
If you don't serve notice first, you could prejudice any rights against a lazy builder for good.