Water vapor is not the same as liquid water, ...
I just checked an Atkinson Noland test of Water Transport Charactersitics of Masonry restoration Mortars and it seems that the ASTM E96 test they used places a square of sample mortar at the top of a cup above the water and sealed so that only vapor can pass. This seems like a better description of a vapor test.
This study tested Water Vapor Transmission, Permeability, and Permeance of the mortar samples. Portland-Lime mortars of Type O and Type K were tested along with brick, St Astiers HHL Lime (three types), lime putty, hydrated type S lime and stone. The mortar samples were fabricated cubes and joints.
http://ncptt.nps.gov/wp-content/uploads/2004-26.pdf
Compressive strengths were also tested here:
hydrated type S -- 115psi at 180 days
HHL Lime 3.5 -- 280psi at 180 days cure
Type O (1:2:9) mortar -- 810psi at 56 days
Type K (1:3:12) mortar -- 475psi at 56 days
I don't know why the other test seemed to suggest the mortar sat in the water. I'll have to re-read that one. This test complied with ASTM E96 also and clearly showed that mortar squares fitted and sealed with caulk in a space at the top of a square container above (and not in contact with) the water. So, water had to evaporate out through the mortar samples tested.
This paper explains that E96 distinguishes between WVT (water vapor transmission), Permeance, and Permeability. WVT is the amount of water in Grams that evaporates through a given surface area over time in hours expressed as g/h*m^2 grams per hour-meter squared. So. a higher number is more permeable.
Permeance is that WVT multiplied by the difference in vapor pressure between the inside and outside of that test container.
Permeablitiy is the Permeance multiplied by the thickness of the sample.
If you have a scientific mind then I'm sure you're all reading this and nodding/ smiling at the obviousness of all this information :- D
WVT selected sample scores:
brick sample -- 3.5
Hydraulic Lime (medium) -- 5.1
Portland-Lime Type O mortar -- 5.4
Portland-Lime Type K mortar -- 5.2
hydrated lime mortar type S -- 7.4
All above expressed in grams per meter hour squared of evaporated water through the sample. So, higher is more vapor permeable.
This test seems to make a Portland-Lime mortar of Types O and K seem fine. But, remember that premixed bags of Types N (for example) do not even have to contain any hydrated lime. They often use ground limestone instead. I don't know if that's as good as hydrated lime. But, I've never seen a premix of Types O or Type K mortars anyway.
The Permeance numbers in the papers should address Tscarborough's concerns because that takes into account the differences in vapor pressures inside and outside the walls. You'd have to have a really sound mind to be able to put those numbers into real world value. Yet... it gives those who are searching for answers a clue.
Wow. That's a lot to think about :laughing: