Previous owner Restore plc waned to focus on its core business of office services and document storage.
Former Restore finance director Harvey Samson set up Castlefield House to buy the Peter Cox business.
Purchase price is £3.6m, of which £2.2m is payable on completion. Restore will receive a further £500,000 at the year end. Three further payments of £300,000 each will be made in September 2013, 2014 and 2015.
Manchester-based Peter Cox claims to be the UK market leader in damp proofing, waterproofing, timber preservation and wall stabilisation. For the year to December 2011, it recorded profit before tax of £800kn on turnover of £15.2m. Net assets at completion were £1.4m.
Restore chief executive Charles Skinner said: “I expect Peter Cox to thrive as an independent business and wish Harvey and his team the very best for the future."