laying laminate over ashfalt?

[kitch]

sorry if this has been asked before but when laying laminate is it essential to use a dpm over ashfalt or will ashfalt be good enough as a damp barrier?
The house was built in 1994 i think and surely the base must also have a dpm under the concrete?

 

[mattysupra]

DPM should be fine if not damaged but use a combi underlay still ( Built in vapior barrier )

 

[kitch]

ok thanks
by the way what is the difference between dpm and a vapour barrier and why do you think the floor has ashfalt/bitumin (not sure but its black) layed on top when surly there must be a sub floor dpm on a house built in 1994?

 

[mattysupra]

dpm is a damp proof membrane. It stops moister from the earth getting into your concrete floor. There are different types of dpm's. Sounds like yours is a surface applied one so the concrete underneath is wet but floor covering etc are protected by the surface dpm. It is very rare to find this in a new house. Yours might not be what you think it is tho.
A vapour barrier is a protective sheet that you put on top of the concrete when installing floating wooden floors to stop moister build up from condensation, sweating etc ,from been absorb into the wood. You dont need one when the floor is bonded to the concrete with a already working dpm.