shower problem

[jonjo]

I'm seeking some advice on a new shower that I have had recently installed. We have a combi boiler and part of the work was to run the water pipes chased just below the concrete floor and up into the shower area. All was well on the day of completion of tiling. However 3 days later ( I think the shower was used twice) a damp patch has appeared on the brickwork on the outside wall that the shower is attached to and which the pipes are chased up to the mixer. I informed the plumber but as I was going away for a week I did not have time to look into getting it seen to. I turned off the water to the house for the week. On my return the patch has got slightly larger. I had the plumber round and he says that the patch is due to the concrete drying out in the direction of the outside wall. He then took off a 6 tiles , but the inside wall was dry? I maintain it is a leak, the plumber maintains he checked the pipes were not leaking before he concreted them in? Surely the concrete would have dried by now and the patch on the wall too? It is approaching 3 weeks, bear in mind the hot weather and the sun shining on the walll for most of the day. The patch is approximatelly a rhombus shape about 3ft high by 3ft wide, and to me it appears the centre is in line with the conector that is attached to the bottom of the shower. Does that sound like a leak or concrete drying out. Obviously a leak would mean the plumber taking off tile and hacking into the concrete to inspect the pipes and making good again - and the materials he should pay for. I have a few tiles lying around but I planned to use them for something else myself.

 

[jonjo]

A while ago I wrote the above message.The plumber has returned, last week, and cut into the cement exposing the pipes around mixer and the place where the feed from the mixer with the temperature regulated water comes out from the wall and to which the shower tubing is attached. He maintains that there is no leak as these are the only bits where a leak can occur and they are dry, and he says that is they way he found them. I do not know if it is true he found them that way.
He maintains as there are no connections/joints in the places where he has not cut in to expose the pipes he installed, there will be no leaks in those areas. However the outside wall has a damp stain larger than ever and does not seem to be shrinking.
My thinking is:
a) If he found the leak and fixed it surruptiously the patch may still grow for a period of time - time will tell.
b) If he has not found a leak, the leak is, must be, in the pipe where he insists a leak cannot occur due to there being no connections, as it is just pipe.
As you can guess the relationship between the plumber and me is to say a bit fraught. His behaviour suggests to me he does not like being accused of producing defective work and so would not, possibly, admit to finding a leak.
He wants to know tomorrow if there is any water on the bits he has exposed, which there isn't. To me that is the wrong question. It should be after a further period of time is the patch growing or shrinking?
Any advice on how to proceed would be much appreciated.