Wet patches on concrete floor - Damp or condensation?

[spytek]

Hi

I have recently had a builder replace a wooden floor with a concrete one on the ground floor of my house. The builder used plastic dpc membrane sheets for damp proofing. He also removed a row of bricks around the outside/inside of the house just above the finished floor and and overlapped the plastic sheet onto the brick work so that the dpc membrane went all the way outside from under the floor.

I've notices that sometimes.. the floor appears damp around the edges near to the outer walls and sometimes you get very small patches near the middle of the floor and near the inner walls too but this is very rare. The dampness comes and goes and isnt there constantly. I asked the builder about it and he says that its just condensation. Is he telling the truth?

I'm planning to have the floor carpeted but am concerned about the re-occuring damp patches. Could some please advise as to whether this is a damp issue or just condensation and how I could protect the the carpet from damage once its laid?

Thanks for your help

Rob

 

[Alastairreid]

did he put down hardcore?, sand blinding?, insulation?, how deep is the concrete?

 

[spytek]

did he put down hardcore?, sand blinding?, insulation?, how deep is the concrete?

I recall that he put some concrete (I'm assuming) beneath followed by the dpc plastic sheets, then some large polystyrene slabs (insulation) and then something other mixture made up of large amounts of sand and cement with a smooth layer on top (screed?). I'm not sure how deep the layer above the insulation is.. but its quite deep.. about 30 cm approx.

 

[r896neo]

If he put 300mm of screed It would be bad news or even concrete for that matter it would be highly unusual and take forever to dry out. how do you know its as deep as 300mm?

 

[spytek]

If he put 300mm of screed It would be bad news or even concrete for that matter it would be highly unusual and take forever to dry out. how do you know its as deep as 300mm?

The builder decided to put some of the radiator pipes beneath the floor and one of the joints started to leak (in the hallway ) so he had to dig up part of the floor again and pipes were atleast 10cm below the surface plus he used the same mixture beneath the pipes before he did the pipework. I'm pretty certain that the damp patches were not caused by the small leak (because the leak was in the hallway and not in the rooms with the problems) and I'm confused because the patches come and go and are mainly near the edge of the outside wall in one room and in the corner of the adjacent room but not all the way along the outer wall of that room.

The floor was done several weeks ago so I assume that it should have dried out by now and if it was a 'drying out' issue then there would be patches all over the floor in all the rooms since he did it all at the same time but this is not the case. So I'm assuming its either dpc problem or condensation and I need to find out which one.

ps. can you actually get condensation on concrete floors because this sounds something new to me since I know you can get it on walls and ceilings but never heard that you can get it on floors too.

Thanks for your help.

Rob

 

[r896neo]

Concrete and screeds is often roughly quoted at a weeks drying time per inch, which if there is 300mm of it is at least 12 weeks.

I agree that the patches seem less like a drying issue but it is possible.

Is your cavity clear and is the ground level outside below the dpc?

 

[mointainwalker]

I thought it was roughly 1 week per cm ? Have I got that wrong ?

 

[Deluks]

Condensation is poss around the edges if he didn't fit an upstand. 20mm or so of insulation fitted up against the wall to prevent a cold bridge.

 

[spytek]

Condensation is poss around the edges if he didn't fit an upstand. 20mm or so of insulation fitted up against the wall to prevent a cold bridge.

I didnt see him put any insulation between the wall and the screed. the only thing between the walls and the screed is the plastic dpc membrane which comes up from the ground and goes up between the skirting board and the wall and then goes in between the bricks to the outside of the wall.

To answer r896reno, The house is an old terrace house built in the 1900's so it outer walls dont have any cavities in them. The DPC plastic membrane appears two bricks above the ground on the outside of the wall.

I'm begining to incline to the thought that it is condensation based on what deluks has mentioned. If I was to lay some carpet down when the floor is dry.. would the condensation return beneath the carpet and cause damage or is it better to lay some plastic sheets beneath the carpet to be on the safe side?

Thanks again for all your comments and advise.

Rob

 

[r896neo]

If it is a solid wall with no internal insulation then condensation is a definate possibility but unless you are blasting the heating a lot and have very poor ventilation i wouldn't imagine it would be that bad but it would mainly be appearing at the walls and therefore edges of the floor so that makes sense as to deluks idea? I assume your not currently living in the house?

Oh and yea sorry 1cm per week is more like it