Reverse Curl & Relaxation - Printable Version
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Reverse Curl & Relaxation - eaadams - 10-03-2012 11:36 AM
Concrete can curl as it drys. This is caused by the differential in drying rates for different parts of the panel.
Scott Tarr did a great article in Concrete Construction last month on curling http://www.concreteconstruction.net/industrial-projects/demystifying-concrete-shrinkage.aspx
I asked a question of CC via Twitter and got an amazing response.
My question was about how to predict reverse curl in a slab based on the RH of the slab. Reverse curl is what happens when a slab 'relaxes' after you put down flooring. It used to be that the flooring would come up with relaxation as a moisture issue as the sub slab moisture would come to the surface and get the slab to 'relax'. Here is the best article so far on the subject: http://www.ctlgroup.com/insights/detail/19
However, new adhesives are holding floors down. But, we still get this reverse curl and it creates what I call a 'mole line' along joints where patching compound comes back up. If you look at the CTL article you will see the result on a gym floor on page 3 Fig. 9.
So, my hope is that with good RH testing I could predict this and avoid it on wet slabs. The answer I got back from Scott Tarr was that that internal RH must be consistent (whether high or low) between the top and bottom of the slab to be assured that "reverse curling" won't occur once flooring is installed.
I am encouraging the editor from CC to print his response as it is an unknown thing in the flooring / concrete world on 'how to do it'. I don't know if anyone @ Wagner knows how to test the RH as a profile on a slab but I know you know the same people ... might we worth weighing in.
RE: Reverse Curl & Relaxation - rapidrhrep - 10-03-2012 07:45 PM
EA: If I am seeing the question correctly, you want to know how to profile a floor, utilizing RH testing, correct? If this is the case, based on the science, people will typically install the sensors at varying depths in the floor, say at 1" depth variances. Of course this is done prior to flooring installation and this will allow you to see the moisture gradient in the slab.
RE: Reverse Curl & Relaxation - eaadams - 10-04-2012 10:21 AM
Yea I was just giving a heads up.
RE: Reverse Curl & Relaxation - CC Solutions - 10-07-2012 07:11 PM
A few other things to consider:
The top of the slab will be drier than the bottom (as long as the slab is drying and has a proper vapor retarder) until the slab reaches equilibrium with its environment.
If there is no proper vapor retarder and the slab is on grade, the slab will absorb moisture from the soil and will not remain at a constant RH.
Realistically, a slab's RH gradient will not remain consistent.