I've heard some excuses but no trains due to excessive dust following
weekend engineering work. What were they doing exactly? This is the
line that was closed completely not long ago to completely relay the
track (I think) so why didn't they do major engineering work when the
line was closed.
I wonder how much the dust cost the London economy? W&C, that would be
Metronet wouldn't it.

They did all major engineering work during the closure, and left some
relatively minor stuff for weekend closures. However, since this is
Metronet, I'd guess that they have left much more then originally
planned.