I have a clay tennis court.  It has not been used for five years and
now is overgrown with weeds.  I recently mowed it down to surface
level and started spraying, and then raking away what I could.  Yet
there is still substantial vegetation embedded in the surface.  My
wife tells me I can't simply pull these out because I will damage
and/or disturb the clay/ash layering.  I don't always listen to my
wife so I have pulled some weeds and lo and behold, some of that ash
stuff does come to the surface.  I don't know if I'm killing the court
when I'm doing this.  My major question is, what is the best way to
restore this court to its former glory.  Should I continue to spray
and rake, then bring in someone to dump a new layer of clay on it?  Or
is there a cost-effective "external contractor" solution to this.  We
bought the house five years ago and the court was in great shape, but
have done nothing with it since so I have zero knowledge of how to
restore and then maintain it.  But I'm willing to try.  I am looking
for suggestions of how I can get this court back into use without
spending an arm and a leg.  We live near Melbourne (Australia) but I
presume the physics and chemistry of these courts is the same
everywhere.  Thank you.

I am not a GA researcher, but I am a tennis club manager with many
years experience in the field.  I would love to help you straighten
out this situation.  However, it would be helpful if I knew what kind
of periodic maintenance and care you already do to the courts.  For
example, do you keep them open year round or seasonally?  At the
beginning of every season, do you scrape off the dead material and
replace it with new clay?  What kind of clay is it (Har-Tru, red clay,
etc...)?  How often are the courts used?  How often are they watered,
and what type of irrigation system do you have?  How often are the
courts rolled?  Brushed?

In any case, to put your mind at ease- it is very difficult to do
irreperable damage to a clay tennis court.  That is one of their
charms.  I have seen clay courts recover from all manner of flood,
drought, caving in, plant infestation, bugs, mold, intentional
vandalism, etc...  So, it is certainly OK to spray your courts with an
herbicidal product, and raking the courts should be done anyway.  If
you end up with a tiny hole, you can always fill it and roll it until
everything is back to normal.

When I go into work tomorrow, I will try to find some resources for
you (if a researcher hasn't already answered the question).  I am in
th USA, so we may have some time difference issues communicating. 
Just don't worry- you're not killing your court!

http://www.leetennis.com/manual_fast-dry.shtml#herb

Thank you so much for taking the time to write this...I am embarassed
about how little I'm going to be able to shed light on answers to your
excellent questions.   With regard to the kind of periodic maintenance
I do....let me simply say, I do nothing.  The court has been left to
die a slow and painful death over five long years of watching all of
our local weed and grass varieties sprout and expand so that we now
have an outdoor museum consisting of all the local, wild, flora. It is
just one court, and it shares the property with our house.  So it is
"open" year round, but we haven't used it for five years.  Our weather
here would make it possible to play all year-round if the court were
useable.  I believe it is red clay...which I am only guessing about
because it is red.  I could snap a digital photo and show you.  No
watering, no irrigation system.  We do have a hose nearby and could
hook up a sprinkler or two.  That is what the former owner did. 
Courts have been neither rolled nor brushed since we moved in five
years ago.  We own a roller (came with the court).  I looked at the
site link you provided but will need to spend time digesting.  Thank
you again for taking the time to write about this.