Concrete slab & insulation

[lngn2]

Prior to Christmas we had a new slab poured. At the time, we asked the builder how long to leave it prior to insulating and were told a couple of days was fine. Subsequently I've discovered that concrete dries at 1mm/day, so the insulation will presumably be trapping moisture in the slab.

 

Today, much to my dismay I've discovered that the PIR upstands around the edges of the floor are damp and there's visible moisture on the DPM. Diagram & pic below shows.

 

Several questions, both relating to this, and more generally. Any help very, very gratefully received.

 

1. Is the issue of trapped moisture going to cause us a problem long-term (if so, what to do)? Will the slab dry with water loss around the edge as we appear to be seeing? Would a dehumidifier help?

 

2. Should the floor VCL be attached to the wall? Otherwise presumably damp air could get behind the insulation and condense on the cold side? I cannot find anything definitive on this.

 

3. If yes to point 2, then I guess works stops (inc plastering) until the slab is dry?

Many thanks...

[Conor]

I had this issue with my tanked basement slab... spoke to architect and the SE that both inside that it was fine. We were moping up puddles of water the day before we put the insualtion down. A year later, no apparent side effects.

 

In your case, I would have thought the main dpm would have gone on top of the concrete slab, not under.

[JohnMo]

It comes out slowly, very slowly.

 

If you are putting a wooden floor on top, you may need a liquid DPC, as moisture levels remained high in ours 18 months after the floor went in.

[Miek]

I wouldn't worry about slab moisture,  the moisture you can see is more likely to be coming from the screed or the atmosphere IMO.