Damp on internal threshold of old / new extension - help!

[meales]

Hi
I hope this is the right place for my question and hope you can advise me. A new extension was added to my 100 year old house. The old back door now steps into the new utility room but the 3 tiles cracked on the threshold. I lifited them and the chipboard flooring on polystyrene insulation has warped and slightly damp. The old threshold (concrete) is damp and my builder reckons this might be caused by possibly no dpc under the threshold? He reckons I could paint AquaSeal liquid membrane on the threshold and cement over it but I'm worried that if the liquid membrane works, it might spread the damp further out of sight! I also sort of think that he should be solving the problem but I would like to be able to say something sensible, like the problem is xyz or puttin g aqauseal will not solve it----but I haven't got the knowledge???
I've attached a picture of the extension groundworks just in case something stands out to a professional. If anyone could spare a comment, I would appreciate it - many thanks.

Untitled

• meales
• 1 Nov 2012
• 1

wooden batten - the DPC seems short with big gap to original wall?

Untitled

• meales
• 1 Nov 2012
• 1

back door removed now and steps into new utilkity room.

Untitled

• meales
• 1 Nov 2012
• 1

looking out into new utility room. The threshold is damp and I had to dig out the cement infill...

 

[TerenceQ]

The first picture says it all if I am looking at it right. The membrane should lap into the walls at the very least and have covered the gap between old and new construction.

Why the piece of wood? That's going to rot.

 

[meales]

Thanks for your reply. I half expected this might be the problem because what I read said the membrane was supposed to be sealed to the old wall and I was surprised to see it didn't make it to the wall and just barely above the cement base. I think the piece of wood was to provide a level for the cement base?
I think polystrene insulation went on top of the base but I didn't get to see that or whether the wood was removed.
I took photos each day when I got back from work because I was interested in the stages of building an extension.
People might say its not rocket science but I was truly facinated and impressed.
Not so impressed with the damp issue - does this mean the floors have got to come up, which will include the living room too. My wife will go mad and the builder will too if I suggest it to him!!!!

Untitled

• meales
• 3 Nov 2012
• 2

 

[^woody^]

If the dampness is coming up a wall, then it will need injecting

If the floor, or threshold below floor, and the liquid membrane can join with the DPM, then you can use that.

Think along the lines of a continuous barrier