Vapor Drive / Osmotic Action & RH

[CC Solutions]

CaCl is a flawed test but it can be used to show relationships. I wouldn't bet the farm on the readings, but under similar conditions with similar installations you will get similar results.

And to clarify, high RH means higher water content not necessarily higher vapor transmission.

Typically a higher RH slab will have the tendency to emit more vapor because it has a lot more water to emit to reach environmental equilibrium.

I hate all these disclaimers I have to write because guys like Bob or Ed will jump in here and find the one slab that is 90%RH and the surrounding environment is 98%RH and the slab wouldn't be emitting any vapor... it would be absorbing vapor!!!

Which then brings us to the problem with CaCl: What kind of reading will we get on a 90% slab in a 98%RH environment when we place a plastic dome separating the slab from the environment and then place a desiccant in the dome creating an artificially dry environment?? The slab may not be emitting any vapor except under the dome!