Condensation like moisture underneath shower tray

[kirk2021]

We have a shower on a solid floor, last year we removed the cover to find that the chipboard supporting the underneath of the tray was wet and rotting so we replaced the shower tray assuming that the tray was at fault as no leaks could be found from the pipes. We contracted plumbers in to replace the tray with a new one due to the condition of the old one assuming that the problem would go away yet the moisture is still there with the new installation and is now beginning to rot the door frame and carpet. Our first thought was that it may be condensation so we installed an extractor fan above the shower cubicle but the problem still remains. we have tried resealing around the tray and the pipes still appear not to be leaking. We cannot figure out where it is coming from can anyone suggest a possible cause?

 

[seco services]

would of said your problem is probably more related to the solid floor
ie no dpc or other issues related to the solid floor.

 

[Burnerman]

Moisture wicking up through the concrete floor due to absence of a vapour barrier, maybe? Leave the shower surrounds off so the area can ventilate.
John

 

[kirk2021]

the shower surround has been off for the last 3 months its well ventilated, theres a huge hole in the floor around the waste pipe far bigger than it should or needs to be we were considering filling it in with concrete today but didn't want to make the job more difficult if that wasn't the problem.

Im assuming this is more than likely the problem then? is there anything specific we need to do before we fill it?