Moisture coming up through slab covered with vinyl tiles.

[capital1965]

Over the past two weeks, I have noticed a damp patch appearing on the bathroom carpet. It has got steadily darker and bigger. The carpet (now removed) was over the original vinyl tiles stuck to a concrete slab. Since removing the carpet it seems there is only a small amount of moisture but obviously the carpet has sucked it up over time holding more and more water. The bungalow was built in the mid 60s. We have lived there for 7 years with no problems till now. There are no pipes nearby so I can only assume the water is coming up from the ground. There is also a small patch in the hallway outside the bathroom, also a slab, but built possibly ten years afterwards when the bungalow was extended. So my questions:
Were 1960s slabs built with polythene DPMs and if so, could this have always been damaged?
Could the massive amounts of rain we have had over recent weeks raised the water table or (some similar natural process), thus increasing the pressure under the slab, forcing the water up?
Would a liquid DPM on the surface fix the problem or just force the water up somewhere else?

Thanks.

 

[crazydaze]

Sounds like a potential water table issue/damp course issue. There may not be a damp course at all or the original may have been breached by the high water table.

A liquid DPM like F-Ball F77 would deal with the issue but would need to be applied to the clean subfloor, the tiles would need uplifting. You would want to screed over the F77 and if fitting carpet, you won't be able to pin the grippers as these would breach the DPM. Fitting grippers with adhesive may cause an issue at some point in the future if the grippers come up with chunks of screed/DPM so something to consider.

 

[capital1965]

Sounds like a potential water table issue/damp course issue. There may not be a damp course at all or the original may have been breached by the high water table.

A liquid DPM like F-Ball F77 would deal with the issue but would need to be applied to the clean subfloor, the tiles would need uplifting. You would want to screed over the F77 and if fitting carpet, you won't be able to pin the grippers as these would breach the DPM. Fitting grippers with adhesive may cause an issue at some point in the future if the grippers come up with chunks of screed/DPM so something to consider.

Thanks, that doesn't sound too onerous. Eventually, the room will be a bedroom with engineered wood flooring when I get around to moving the bathroom into another room. This will be floating over an underlay with a built-in DPM.

 

[crazydaze]

You need a DPM in the subfloor to install engineered wood. The underlays with inbuilt foil etc are designed to prevent small amounts of residual humidity, NOT act as a DPM.