BigWallop wrote:
A good idea is a low grade belt on one of those industrial jobs of a sanding
machine.

Low grade == fine? Any suggestions on what grade. I've never used one
of those big floor sanders but always assumed they came with belts
rough as Gerry Halliwell to remove a hefty layer of wood.

The grade of roughness on the sanding belt determines the job on
these things, and you don't need to remove loads of surface to make the job
of re-varnishing easier for you.

I don't want to remove a load of surface, I really just need to remove
the old varnish as the boards are in pretty good condition.

An industrial sander is the easiest way to go with finishing something like
the job you have. It really makes light work of smoothing new to old boards
a lot easier anyway. Trying to remove even a few millimetres from the
difference in the thickness can be a real chore with a hand sanders, no
matter how patient you are.

Now that's a good point, I hadn't really considered sanding as the way
to level the new boards to match the old. 90%+ of the new boards go on
an area where I've to put in new joists, so I was planning to mung the
joists to fit rather than the boards.

My preferences on all this you understand, but just trying to make your life
easier. :-)

Thanks for all the advice, it's a big help and I do appreciatte it.