Moisture on basement floor

[Gavro]

Morning all. First post. Apologies if this is in the wrong place, i couldn't see anything specific for this issue.

I recently moved into a back to back terrace.
The basement is painted brick walls and concrete floor and consists of a large room and two smaller ones. The previous occupant stored guitars, dj equipment etc in the basement and it looked and feels quite dry. I'm having new meters installed this week so emptied out one of the smaller rooms, which has plastic sheeting down. When i moved in the previous occupant left all their belongings and i'd not got round to emptying this room until this week.

When i pulled up the plastic sheet there's moisture underneath. I'm sure this is condensation gathering under there because it's only where the sheet is and the damp pattern mimics the creases in the sheet, but i want to check. I've attached photos. If i take up the plastic and empty the room, add a dehumidifer and heater, will I be able to determine whether it's damp coming up through the concrete or not? In the meantime i'm checking gutters, pointing etc Thanks

 

[yorksbuilder]

It all depends on how much ventilation there is in the basement.
Is there carpet on top of the plastic?
Check all your drain gullies around the house and drain pipes and position of DPC etc.
If you want to be sure whats going on you should check the moisture content of the concrete now and in wetter/drier times and see.
Recommend having a dehum going down there anyway if you are using the basement

 

[Gavro]

It all depends on how much ventilation there is in the basement.
Is there carpet on top of the plastic?
Check all your drain gullies around the house and drain pipes and position of DPC etc.
If you want to be sure whats going on you should check the moisture content of the concrete now and in wetter/drier times and see.
Recommend having a dehum going down there anyway if you are using the basement

Thanks for replying.
There's no windows. A can see a vent in the main area (where the floor is fine).

No carpet. The last owner has just placed plastic sheeting down in one room. Which i assume is a bad idea whether there's moisture coming up through the floor or not? At the edges where the sheet was too short to meet the wall there's no moisture.

 

[JohnD]

The damp is coming up through the floor. Covering it with plastic prevented it from evaporating off, escaping, and drying out.

If it had been condensation from the air In the room, it would have formed on the room side of the plastic.

It is normal for cellars to be damp. Copious ventilation will allow the water vapour to escape.

It is very difficult to fully prevent the damp, but you would have to dig out and relay the floor, and construct false walls. Water could collect behind these barriers so you would need a drainage system with a sump, and an automatic pump.

Until then, do not use any floor covering (except loose permeable matting). Do not put any solid furniture or boxes on the floor or walls. Get some plastic shelving units that stand on plastic feet so air can circulate round them.