The plaster used to repair or re-plaster squash courts should be some product like Armourcoat or Proderite that is specially made for squash courts. I think it is rubber-based and one of the few suppliers in Ireland is Classic Walls from Derry see www.classicwalls.com for more information. This firm will do the job or supply the plaster for the job. Certainly you should NOT use regular plaster. They can supply repair packs for different sized areas.
Painting the Walls:
For a good job you need the proper paint and a Glixtone product supplied by Graffiti Solutions in Dublin has been used successfully. You can visit their website here and read the technical data-sheet here. This product will cost about €90 (inc V.A.T.) for a 5 litre tin and you'll probably need 3 tins for a court. You should give it two coats and that might be done with 5 tins? (The manufacturer of the previously recommended Armourcoat poduct has closed so Pat McDonnell Paints no longer stock it and their replacement product is not designed specifically for squash courts.)
Most floors will take a sanding a few times before it becomes problematic to do so. However, you should use a professional (carpenter?) who will use a belt sander lengthways and not across the grain. The carpenter should be asked to make good any ‘dodgy’ floorboards as part of the job. You should be able to get this done for anything around €250 / €300 per court (?). It takes a day to do a court (?). You will need a lot of voluntary work from your members to vacuum the courts and surrounding area once the sanding is done. Remember to wipe down the walls and light fittings before you start vacuuming! This cleaning will have to be done many times before using the courts again as it takes days for the dust to settle. You should then clean off the courts with something like white spirits.
You are better off not to apply any floor varnish when the sanding is done but club members have to be told to use court shoes in future and not simply non-marking shoes. The difference is that you want them going on court only with shoes used exclusively for squash! If you are lax in this area it will result in marked courts and a recurrence of the problem.
The court markings should be renewed using some strong and quick drying FLAT paint.
Cleaning the squash courts:
The first point to stress is that brushing squash courts is not a good idea. It causes the dust and dirt to be moved about thereby smearing the surface and dust will lodge between the floorboards only to rise again once the players run about the court. It also causes a greasy film to be formed on the surface and, over time, the courts become slippery.
Ideally the courts should be vacuumed a couple of times per week and a damp cloth wrapped around the brush head should be applied to the courts maybe weekly to remove any dirt.
Players should be required to use non-marking squash shoes that are not worn anywhere else. (Merely requesting non-marking shoes will not keep your courts clean if the players use them for other sports or indeed use them outside the squash courts. The shoes become dirty and then mark the courts)
England Squash provide technical information sheets that can be accessed on www.englandsquash.com .