Laying new floor, possible damp problems

[danboy775]

I just ripped up my carpet in my bedroom as I am planning on laying laminate. The back part of my house where the bedrooms are seems to get a bit damp, nothing major really just a faint fusty smell now and again.
I put it down to lack of air circulation as none of the windows have vents in them. I am now going to fit trickle vents to all my windows in the bedrooms.
Anyway I ripped up the carpet and the old underlay and noticed something that looked like salt on the concrete floor and stuck to the bottom of the underlay, I've attached some photos.
Any ideas what this is?
Also, is there something i can treat the concrete with prior to laying my laminate to prevent any further damp issues?

 

[dazlight]

How old is the house.
Yes you can apply 2 coats of liquid dpm.

 

[Gerrydelasel]

In a pinch you can also put down a polythene DPM

 

[danboy775]

Can I do both for good measure, apply liquid DPM then also use a polythene DPM?

 

[Gerrydelasel]

Of course. You can forget the laminate and just smear the polythene with grease and slide about on it like a giddy child if you like. Makes no difference.

 

[danboy775]

Haha that sounds like fun, not sure my girlfriend will be too impressed though!
Any recommendations on which DPM's I should use?

 

[Gerrydelasel]

Since you're effectively using two DPMs I suppose it doesn't matter. If it was just one then you'd definitely want a decent thick polythene, like 1000ga.

 

[cwhaley]

I find trickle vents a bit rubbish to be honest. They quickly get clogged up with insects and cobwebs and only really allow a small amount of air (plus water vapour) out of the room.

What solved our problems with damp in some rooms was leaving the window locked on the catch during the day. Yes it can get cold, but if they're shut in the evening and you don't dry clothes in there, the circulation of air is much, much better.