Teachers Mutual Bank is expecting to complete its merger with Fire Brigade Employees' Credit Union by November 1, when it will launch its new brand Firefighters Mutual Bank.Teachers has adopted a multi-brand strategy to recent mergers. Last year it completed a merger with Uncredit, which is now trading as UniBank.Teachers chief executive Steve James said the multi-brand approach made the group "nimble and adaptable".The cost of the merger had an impact on Teachers' bottom line in 2015/16. While assets grew by 14 per cent to A$5.5 billion, net profit increased by just 1.4 per cent to $30.2 million.The mutual bank's net interest margin fell from 2.5 per cent to 2.37 per cent.The mortgage portfolio grew by 14.2 per cent to $4.3 billion. James said Teachers distributed through a network of 13 aggregators and had introduced UniBank products into the network during the year.In May Teachers stopped selling mortgages to investors, announcing that it had failed to get its investor mortgage sales under the ten per cent growth limit set by the Australian Prudential Regulation Authority. It returned to the investor market in August.Retail deposits grew by 13.9 per cent.The merger with Firefighters will add $215 million of assets and 7400 members to the current member base of 177,357.Teachers' capital adequacy ratio was 15.85 per cent.James said the mutual bank's technology investment over the past year was focused on the installation of Dell Boomi middleware, which would give it a "plug and play" capability using the application programming interfaces in its Ultradata core system.This would make it easier for Teachers to add new apps. It has been working with a group of fintechs in KPMG's Mlabs hub and plans some announcements later in the year.