Dr. Judith E. Selwyn
Preservation Technology Associates, Inc.
285 Reservoir Road
Chestnut Hill, MA 02467
 
617 598 2255
fax 617 277 3389
 
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From: The listserv where the buildings do the talking
[mailto:[log in to unmask]] On Behalf Of [log in to unmask]
Sent: Friday, March 26, 2010 11:57 AM
To: [log in to unmask]
Subject: [spam] [BP] salt and pepper
 
See comments in blue - Judy 

The new university campus at ole Miss is troubled  in effloresence ; 
while the more historic part is by and large free .

The resons vary ; but my humble take is the new sections have cast stone
instead of limestone ;and what we are finding is that cast stone  on only 3
inches thick  becomes more and more porous over time ....limestone does to
;but it seems the cast stone holds and takes on more water ; the second
culprit often is the roofing detail ;undersized scuppers and gutters
;allowing splsh back  into the brick and  masonry 

Overall the most  likely culprit is the flashing detail . In the past stone
was set on a bed of mortar with the lead or co[pper flshing only going
partially under the stone .
Now it seems that the cast stone is set on through wall flashing ( fire and
ice  shield ) then pinned with an  Rt angle bracket to its interior return
and  into the brick  substrate ....and  then  set on a bed of mortar . And
you do not have a bond between the flashing and the substrate below -
letting in water?
 

In the recent past 70's and 80's  this was not the case; and we see all
sorts of pins and all sorts of lack of detail  that can allow water to
filter in   

many new  bricks used here are hollow cavity bricks; where often the mason
drops mortar into and thus creates dams for the salts to collect and travel
out in to  

I don't know about today but zinc cloride was an additive ( to make mortar
harder) for early strength  that was used alot at one time . /

speaking of salts ...the doc sez I got to cut it out ....no good for me
....How come all the good stuff is "no good" for you ?  /Py




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