Undercoat

The kind of undercoat depends on the kind of varnish to go over it, i.e. they must be compatible. The undercoat needn't be as effective in sealing as the finish coat. Instead of a base coat especially designed for that purpose, often simply a coat of thinned finishing varnish is applied.

The purpose of the base coat is to:

• strengthen the exposed cells in the wood.
• ensure proper bonding of the varnish to the wood.
• shield the wood against varnish components, i.e.
• keep them from affecting, i.e. changing the color, or
• prevent them from loosening the adhesive joints, and to make the surface uniformly absorbent.