Although surfaces can be painted or varnished without using a primer, there are benefits to using them. Using a wood primer can offer a cost saving on just using the top-coat product over large areas, for example using a primer on a wooden floor before varnishing. 1 coat of primer and 2 coats of varnish rather than 3 straight coats of varnish. Primers help to provide a smoother, more professional looking finish. They help with adhesion and longevity of the top-coat. Paints that offer a specified time guarantee i.e. '10 years' usually require the use of a specified primer from their range to uphold the guarantee.