Using a subprime mortgage to access a loan and then paying it off can actually help to repair your credit over the long term. Building a history of on-time payments and financial reliability will, over time, improve your credit score. By using a subprime mortgage to do this, you may actually help yourself qualify for a regular mortgage in the future. This pendulum swings both ways though: if you miss payments on your subprime loan, it will have a negative effect on your credit.