[Ferro List] 3 questions for Walter

[Keith B]

Hi Walter

I used vermiculite with waterglass based binder for kiln repair and 
rebuild (too hot for OPC) but figured it too fragile for lower 
temperature use, as it wouldn't stand mechanical mixing.  It's good to 
know from your success hand mixing is a viable option with OPC. 

 For mechanical mixing with OPC, I used perlite instead, ignoring a good 
deal of attrition.  I needed a semistructural product, and the fines 
produced gave about the properties I wanted.  (Similar material has 
withstood year round weathering  in a Maryland fountain for ten years, 
with no visible damage and no hard surface.)  Your mix was instructive 
though.  I could never achieve workability without a w/c ratio that was 
horrible, because so much of the water instantly vanished into the 
perlite.  You seem to have been able to use a nominal w/c of 0.5, 
presumably actually quite a bit lower for the cement matrix, so you 
probably got really good mechanical properties from it.  That probably 
gets you decent strength from effectively a cellular cement, plus a 
thermal performance on the high side of what one would expect for 40 pcf.

The question about porosity and water from the building interior came 
from research papers on arctic construction which turned up some years 
back when Janoahsh first joined us.   It turns out that  water vapor can 
pass through OPC based mortar capillaries which are too fine to pass 
liquid.  Under an appropriate temperature gradient, it can thus 
continuously diffuse from a warm interior to condense in small voids 
under a cold exterior,  freezing and spalling off the exterior facing.  
You may not get cold enough for that, but it sounds like the cover you 
plan would protect anyway, even in Alaska.

Thanks for the info.

kb