Robert wrote:
Hi,

Some rust spots have appeared on my window sill. I am sure these must
be the nails heads. I can imagine some condensation may have wet the
sill but I am surprised the nails have rusted. I sanded it back to the
wood and painted with primer and undercoat that were both solvent
based. Shouldn't they have kept the water out? The top coat was that
new Dulux water based gloss (yuck!). What is the best thing to paint
over the nail heads with to stop the rust stains coming through again?

Thanks in advance.
Robert.

Use knotting and fill the holes with a non-water based filler.

As a matter of interest, what filler did you use before painting?