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+--- Thread: RH Numbers Rising (/showthread.php?tid=119)
RE: RH Numbers Rising - CC Solutions - 09-09-2011 08:11 AM
(09-08-2011 06:08 PM)eaadams Wrote:(04-18-2011 04:46 PM)eaadams Wrote: I just had a GC in Los Angeles tell me they can't get the building acclimated because they can't get heat on until they get the occupancy permit and cant get occupancy permit until flooring is done ....
sounds crazy to me.
Same GC's rH tests by George Donnelly just came in at 99%.
FYI learned he uses Vaisala equipment not Wagner.
Can't a slab ever just be dry 12 months later
If George used Wagner equipment he wouldn't have to worry about calibration and setting the reader to the probe to get the variation correct, he wouldn't have to let the probe equilibrate for about an hour, he wouldn't need to re-calibrate yearly and check calibration monthly, and he wouldn't have to worry about keeping all these calibration documents on file when a question comes up about accuracy!
Slabs can dry just fine in 4 months if the entire team takes responsibility to achieve that goal!
RE: RH Numbers Rising - rthompson - 09-09-2011 09:36 AM
There are companies that can place temporary heat or cooling prior to the activation of the HVAC. Trouble is it costs money! But you kknow the American way "low bid mentallity spend anything to fix it"
RE: RH Numbers Rising - Ernesto - 09-09-2011 04:48 PM
I remember reading something about heat drying slabs, I thought it said it can come back to bite ya after the heat is turned off and the soils re-equilibrate, mositure goes right back into the slab. But then maybe it was just a dream.
hmmm, where was that?
RE: RH Numbers Rising - CC Solutions - 09-10-2011 07:47 AM
Now how can moisture get back in the slab when there is a proper vapor retarder under the slab as dictated by F-710????
Besides, you can't put a moisture sensitive flooring on a slab on grade without a functioning vapor retarder under it. All adhesive manufacturers require a vapor retarder under the slab.
So whoever told you that is wrong. Soils should have nothing to do with slabs.
RE: RH Numbers Rising - Ernesto - 09-10-2011 11:14 AM
(09-10-2011 07:47 AM)CC Solutions Wrote: Now how can moisture get back in the slab when there is a proper vapor retarder under the slab as dictated by F-710????
Besides, you can't put a moisture sensitive flooring on a slab on grade without a functioning vapor retarder under it. All adhesive manufacturers require a vapor retarder under the slab.
So whoever told you that is wrong. Soils should have nothing to do with slabs.
You should add "proper and functioning" to that. I never see anything from adhesives manufacturers stating that.
FLOOR SLAB LAID DIRECTLY ON THE GROUND
The above diagrams and correction factors can also be
used for a floor slab laid directly on the ground if the
actual slab thickness is doubled. This presupposes that no
drying occurs downwards. This is the case, for instance,
if the slab is underlain by a layer of extruded
polystyrene. If expanded polystyrene is used, some
drying may take place through this, and the drying times
will therefore be a little shorter than those obtained from
the diagrams.
When a floor slab laid on the ground is underlain by
ca 5 em mineral wool insulation, drying can in most
cases occur downwards. Nilsson /10/ has stated that,
because of this drying, the drying times in the above
diagrams (with doubled thickness) can be multiplied by
0.6-0.7, provided that the width of the building is less
than about 10m.
Blomberg /19/ has calculated the temperatures for the
case when the construction is completed in the summer
when the ground has warmed up. The results of these
calculations show that, even during a normal summer in
Sweden, drying takes place downwards through the
mineral wool. It is however shown by the calculations
that if the summer had been exceptionally warm, the
temperature difference across the insulation which is a
prerequisite for drying downwards does not occur around
the outside of the slab. In such a case the factor
0.6-0.7 should not be used, and it should be assumed that
drying occurs from one side only.
If the mineral wool is very wet when the concrete is
poured, it is probable that drying downwards is not
possible, and the factor 0.6-0.7 cannot therefore be used.
Nor can the correction factor 0.6-0.7 be used in
calculating the drying time when there is a plastics foil
between the mineral wool insulation and the concrete. In
principle, this case is the same as when drying takes
place from one side only, i.e. the case with expanded
polystyrene underneath the slab.
WARNING. If a floor slab is dried during the construction by heating, this may also
cause the ground to heat up. Moisture can then be transferred from the ground to the
concrete when heating stops.
RE: RH Numbers Rising - CC Solutions - 09-10-2011 06:30 PM
What is all that copied stuff about slabs in Sweden?
A slab in direct contact with the ground will dry, that's not the issue. It will not get as dry as a slab with a vapor retarder, and if you put a sheet vinyl floor over a slab in contact with the soil the slab will get wetter.
RE: RH Numbers Rising - Ernesto - 09-11-2011 08:22 AM
(09-10-2011 07:47 AM)CC Solutions Wrote: Now how can moisture get back in the slab when there is a proper vapor retarder under the slab as dictated by F-710????
Besides, you can't put a moisture sensitive flooring on a slab on grade without a functioning vapor retarder under it. All adhesive manufacturers require a vapor retarder under the slab.
So whoever told you that is wrong. Soils should have nothing to do with slabs.
Vinyl is installed over slabs all day long that don't have "proper" vapor retarders. And there's this other area of flooring installation out there called residential and probably just as many builders of residential do not know what a proper vapor retarder is as commercial builders. Not to mention how easily they can be damaged on the pour.
RE: RH Numbers Rising - rthompson - 09-11-2011 08:25 AM
A slab on-grade with no vapor retarder can wick moisture as deep as 20 feet, depending on the fines content of the soil. That same slab is also capible of wicking moisture vapor as deep as 80 Feet. Any slab that is placed on-grade without a vapor retarder is not in compliance with ACI 302 or ASTM F710. Moisture will travel in and out of a dry slab due to humidity changes. In essence a contrete slab is a sponge in cement clothing.
Regards
Rayt
RE: RH Numbers Rising - Ernesto - 09-11-2011 08:40 AM
Thats how I explain it to my clients Ray. It is absolutely like a sponge and worse. The sponge is filled with alkalinity. Either pay for moisture prevention or pay lots later.
I just wanted to make it clear to people that merely heating up a slab to dry it can still have consequences and in the residential arena no one really knows or documents how the slab is protected in most cases.
RE: RH Numbers Rising - CC Solutions - 09-11-2011 03:54 PM
I realize all the problems with the flooring industry, and the poor quality of slabs installers run across. My position is to educate about those problems and advise remedial measures.
When a slab is poured directly on the soil, you have no warranty, none, nada, zip, zilch, from any adhesive manufacturer. An installer should advise every owner that their warranty is directly affected by the quality of the slab and the vapor retarder.
I would never install a floor on a slab I was unsure of without a long discussion about the possible perils and the owner fully buying into the course of action. Why? Because I can make that slab failure-proof with a little money to do so. If the owner wants to cut corners, then I would either leave or promise there is no warranty....
(09-11-2011 08:25 AM)rthompson Wrote: A slab on-grade with no vapor retarder can wick moisture as deep as 20 feet, depending on the fines content of the soil. That same slab is also capible of wicking moisture vapor as deep as 80 Feet. Any slab that is placed on-grade without a vapor retarder is not in compliance with ACI 302 or ASTM F710. Moisture will travel in and out of a dry slab due to humidity changes. In essence a contrete slab is a sponge in cement clothing.
Regards
Rayt
I fixed a slab in Vegas in the middle of the desert because of excessive moisture. I mitigated one built on top of a 100 foot tall hill that was sand as far down as an excavator could dig (and they dug pretty deep to put in elevator pits in the basement).
