I am going to be hiring a contractor to stain the front of my house,and have been getting different advice on how to. It is somewhat dirty and old,does it need to be treated or just powerwashed? neither/both? If I were to use a darker stain than is on there now do you still wash? put on 1 or 2 coats? reason i ask is cuz of 300% difference in some estimates!?!?