Hammann was appointed assistant editor of Huisgenoot in September 1977. He became an editor for the magazine in 1978. Huisgenoot and You are published in Cape Town by Media24, an affiliate of the South African media giant Naspers. In the late 1970s, Huisgenoot's weekly sales dropped to 129,000, which made the publication's owners think about shutting it down. Hammann prevented Huisgenoot from closing and systematically revived the magazine. This was done in part by focusing on seasonal stories, celebrities, and crime. He also opened syndication offices in London.
The magazine's circulation grew to more than 500,000 in 1984 and reached a record high of 540,000 sales in one week in the 1990s. Huisgenoot had become the leading South African weekly. It was read by considerably more than two million people every week based on an average issue readership of more than four per copy sold.
The magazine You, which Hammann launched in 1987 as a form of English "clone" of Huisgenoot, followed the same upward spiral from the start. It soon achieved second place on the popularity list for South African magazines. As with Huisgenoot, Hammann molded You's content to meet international standards, which he had previously studied as London editor for Naspers's magazines.
Hammann retired in the late nineties.