Do I have a damp problem?

Oki2

Recently pulled up the carpets on the ground floor of my 2 bed 1940's semi. 
The existing underlay had a waterproof base which was wet underneath (this had not soaked through the underlay), and underneath that were some very old, thin tiles which were also wet. Under the tiles is concrete (the tiles are quite loose). After a a few hours, the tiles were dry and now a couple of days later the floor feels completely dry to touch so I assume this was condensation.
However, I've had a carpet fitter out to get quotes on new carpets. He showed concern about the loose tiles (some of them were also raised on the corners) and said that we could have a damp problem when I told him about the old waterproof-backed underlay and the fact it was wet when I lifted it. 
Anyone had a similar experience, and was it indeed a damp problem?

Jeepers_Creepers

Most likely, yes.

I suspect it's a small amount of damp coming up through the concrete floor due to it not having a proper DMM, or it's been damaged somehow. This small amount of damp would normally evaporate away if the floor was exposed, but the presence of the tiles - and also your underlay - prevents that from happening (no air to ventilate it), so the damp builds up.

I'd certainly have these tiles removed - they ain't helping - and then I guess the simplest solution would be tanking slurry to seal the floor. But I think you may need proper advice on this.

I certainly wouldn't put a new carpet down on that.

Jeepers_Creepers

Is it in just one place on the whole floor? Where abouts?

Oki2

Thank you. It's pretty much the whole floor. 

Oki2

Probably worth mentioning, my grandparents owned the house previously. And although I'm not aware of why they never took up the tiles, I do know that they have never had any problems with damp and the carpet I removed has been down for around 9 or 10 years.

Jeepers_Creepers

If you expose the floor, remove the tiles (you really don't want them down anyway, do you?) and then place an upturned bowl on the floor and leave it for a few hours, if - when you lift that bowl - you have bowl-shaped damp under it and not elsewhere, then it's coming up from the floor.

Oki2

Good idea - thanks for the tip