We use Dpm's to surpress construction moisture or just high levels of moisture in subfloor slabs to speed up the installation of floor coverings ! BUT if the moisture is being suppressed from rising through the top of the slab & an effective ground DPM is surpressing moisture at the bottom of the slab.... Where does the moisture go if not up or down ? Does the slab ever completely dry out ?
Dpms slow the rate at which the moisture rises through the surface mate. so much to the point that it doesn't upset the bond between screeds & adhesives etc. so the slab does indeed still dry out albeit at a slower rate.
Sorry don't mean to sound thick was just wondering where the moisture goes if its sealed in sort of ?
as I understand it, it's not 'sealed in' by a surface Dpm. only suppressed to a much slower degree. so Evaporation....
They(dpms) let the moisture out at an acceptable rate so the floor covering doesn't fail. In laymans term lets the damp out very slowly.
OTE=Spacey;84981]So where does the moisture go then ?[/QUOTE] Hopefully into the plasterboard then its not my problem
Hopefully into the plasterboard then its not my problem [/QUOTE] That's what I was thinking into the walls but again not my problem Lol
I know its a bit different but when screed is left to dry in a sealed building with bad or no ventilation the moisture & condensation on the windows the next day is unbelievable & that's only a 3mm or so coat so there must be a lot more moisture coming out a slab ?
there is yeh, but then slabs arnt laid in a sealed room with no ventilation They are laid and left for months with a lot of time no walls or windows in! lol
Most the time but not always Cheers for the replys Just my little brain making much a do about nothing !
I got told the count down of a millimetre a day upto 50mm and double days per mil above that doesn't start till windows and lid goes in, as the slab will be drawing atmospheric moisture and slows the drying out to next to nothing
and don't let the customer dry their washing in the same room as the moisture from the clothes will get sucked into the slab.. lol
lol had that a few yrs ago, slab had been down for over a yr, none of us could fathom why slab was still in the late 80's early 90's rh. I turned up unannounced one day to check readings and she had one of these old style roof hanging clothes airers with clothes wringing wet!! turns out that's how she does her drying, and what the rooms is for! ffs
same thing here, turned up in a conservatory.. told her off... 3 days later with 2 windows open and not opposite each other and it was dry.. customers..lol
This is something I have always thought about ......wouldn't it go sideways and up the walls ?? ( I'm not being clever ....I don't know !)
Spacey - "Cheers for the replys Just my little brain making much a do about nothing !" No your not Spacey. It's a good conscientious question and an important one at that!! The way I understand it, a moisture suppressants (the abbreviation of 'dpm' being extremely mis-leading with emphasise on the 'proof'), act like an evaporation regulator. In other words they are still permeable. I compare it to a resistor in electronics. The suppressant (as others have mentioned), slows down the evaporation rate of the moisture in the concrete. The moisture will pass through a permeable floor covering such as timber at a rate that will not effect it. Can't remember the terminology of the evaporation rate that a timber floor will accept, perhaps Matt will no.. In effect the dpm is a semi-permeable membrane.
