The Big Four banks continue to sell eight out of every 10 mortgages, despite efforts by their rivals to claw back some share. Mortgage broker AFG reported yesterday that the big banks accounted for 81.7 per cent of loans written by its brokers in July.AFG's figures show that the Big Four have held an 80 per cent share or better in every month except one over the past year.AFG's mortgage sales fell 3.7 per cent in July. The group's brokers wrote 5937 loans worth $2.29 billion, compared with 6205 loans worth $2.38 billion in June. The value of mortgages sold by the group increased by 8.6 per cent over the 12 months to July, which is a little ahead of the seven per cent system growth reported by the Australian Prudential Regulation Authority.First-home buyers made up 13.6 per cent of the market, investors 35.6 per cent and borrowers refinancing 39.1 per cent.Broker Mortgage Choice reported this week that demand for fixed rate loans was increasing. The company said 13.3 per cent of loans written by its brokers in July were fixed rate. This is well above the 12-month average of 10.45 per cent.