In article .com,
says...
snip

Third mistake: since the old skirting was nailed on I decided to repeat
this
attachment method. I punched the oval nails under the surface of the
boards,
then wondered how to cover the heads (the plan was to varnish the
boards, not
paint them).
snip

Glue the skirting with Gripfill. MDF is for painting. :-)