Use a wood filler to fill any visible cracks or imperfections - fine
surface filler for interior work, waterproof or epoxy-based wood filler
for exterior use. If the wood has been treated with creosote use an
aluminium sealer before applying a standard wood primer.
Fill any cracks or holes with interior or exterior wood filler. Leave
it slightly proud when pressing into crevices and lightly sand when set.
Wipe the entire surface with a clean cloth before starting the paint job,
to make the surface dust free.