Damp concrete floor - next steps?

[dormermike]

Hello

Got a small utility room, it has damp patches appearing when the floor is sealed. I plan to put lvt down but I want to address the moisture issue first.

Room is on an outside wall, is 2x2m and has a wall mounted boiler, floor standing washing machine, incoming water main, and 2x outgoing pvc pipes one for the washing machine and one for the adjacent bathroom bath. No window.

The damp patches only appear when something impervious is placed on the floor, e.g. vinyl sheet.

See photo.

I believe there is an old drain pipe that runs beneath this room which was discovered on a CCTV drain survey many years ago.

Shall I dig the floor up, ignore it and move on with life, or CCTV the drains again? Incoming water main isn't leaking confirmed by stop cock off for an hour & meter check. Outgoing uPVC pipes are sound. Cavity was dry when inspected. There is no DPM. External ground is paving stones 6" below DPC, and then a lower soil level.

Thanks

 

[Wayners]

I would dig.
I would want you know

 

[noseall]

Hello

Got a small utility room, it has damp patches appearing when the floor is sealed.

So have most floors when you place an impervious membrane (vinyl etc) above.

 

[dormermike]

So have most floors when you place an impervious membrane (vinyl etc) above.

So it's expected? I'm surprised, as I thought it had to be bone dry before I can lay a finish on top.

 

[noseall]

So it's expected? I'm surprised, as I thought it had to be bone dry before I can lay a finish on top.

Take yge vinyl up and let it air.

 

[dormermike]

Take yge vinyl up and let it air.

I have, the vinyl has been up for weeks, that's just a patch to see if the damp spot returns. I've also had a dehumidifier running in there, which has pulled a lot of water (actually more than this little unit ever has, so was pleasantly surprised to see it works!).

The adjacent room had a very bad shower leak for many years, and it did show on this side of the wall (the wall is the back of the shower) so I wonder if it's still drying out.

My worry is if I put a waterproof screed or similar down, will that move any potential problem to another room? We have oak flooring outside of this utility room, been down for years.