What concrete mix should I use to cover a mud based cantina floor?

Suggest you get this system to lay under the concrete. I have used it, and with a bitumen shield on the wall it works well, plus ventilation outlet to outside. If you can, also put a drainage channel to the outside using the green perforated plastic piping. Also put a steel mesh,20x20cm on top of this for strength and then a 5cm concrete layer.

I'm not sure that using Cuprolex onto a wet earth floor will achieve anything very much, I'm afraid. There isn't really any way around your excavating enough of the earth from the floor of the cantina to give you the space for a 'proper' concrete sub-floor. If you dig out a matrix of deeper 'ditches' into which you can create a concrete foundation, you will be able to reduce the amount of digging somewhat. However, you should check if there are any local by-laws or building codes that are going to be needed to be complied with first. A drainage channel around the walls would be a good idea, with the drains emptying into a deeper 'sump' so that any water collected could then be pumped outside into the house drainage system. If the water ingress proved to be much you might consider installing an automatic pump to help evacuate the water from the sump whilst you tackle the cause of the water leak. Once you have the drainage channel and sump in place, together with the foundations for the floor, you can consider using either a flooring system, such as the Cuprolex Windi sytem, followed with a steel reinforced concrete layer to support whatever floor covering you want to finish with such as tiles, or just pour a concrete floor over D98 steel reinforcing mesh over a decent waterproof membrane to a depth of around 10-12 cm. If your floor is larger than 5mt x 5mt you will have to make sure that expansion joints are in place to stop the whole thing cracking. As far as your walls are concerned, if the problem of water ingress is as bad as you describe, you really need to do something about stopping the cause of the leak. You are correct in that simply rendering up your inside walls will achieve only a faster deterioration of your walls. The only place to put a water barrier in place is outside your house, in between the source of the water and your walls - not a job for the faint-hearted. Rendering (or tanking) the inside of the walls will only result in the stone or bricks - or even concrete for that matter - splitting open and disintegrating in a very expensive way as the moisture levels build up and the trapped salts expand. Good luck with it and if you are not completely confident in your abilities to deal with the problem without actually making it worse, get a builder (or three) in to check out the job and give you a qute. A chat with a local geometra would be a good idea as well, if it is as serious a problem as you describe. Beery.

This sounds like a job for a geometra - use a local one - he'll get all the required permessos [there are bound to be some needed], and he might just get the council to look at their drain!