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RE: Condition assessment for old brick walls

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Jordan,

You are probably not facing an "end of life" event.  The deterioration,
caused by crystallization of salts carried to the masonry surface by
moisture, indicates that the building probably has a moisture penetration
problem that needs to be solved as part of the repairs.  The repair
procedure is called repointing.  Repointing of deteriorated mortar joints
and replacement of damaged bricks are maintenance tasks.

This kind of damage starts at the exposed surface where moisture evaporates,
and slowly [over a period of years, usually] progresses into the wall
following the recession of the sound masonry surface.  Thus, you can scrape
or brush away the dust and very soft material and finally reach the surface
of sound masonry that has not been damaged by moisture that has migrated
thru it to reach the surface.  The best source for understanding and solving
this kind of problem is probably "Preservations Brief 2, Repointing Mortar
Joints in Historic Masonry Buildings" available from the National Park
Service on line at www2.cr.nps.gov/tps/briefs/brief02.htm .

If this is an old building, don't expect sound mortar to be as hard as
modern mortar.  Even the best mortar can probably be eroded by rubbing your
thumb across it, but, except at the obviously deteriorated areas, it's
probably in about the same condition it was when the building was new. 

The mortar in an old building was probably not made with Portland cement, or
else with very little.  Mortar for repointing should not use very much
Portland cement.  It should not be modern Type M or S; better is type O, or
N.  Harder, stronger mortar is detrimental to old brick masonry because
volume changes caused by moisture and temperature variations lead to the
hard mortar working against the softer brick.  To do the repairs, try to
find a mason who does masonry maintenance and repair -- there are bound to
be some out there, even though we who design new buildings rarely have
occasion to meet them.

Be sure to find the moisture source and get it under control: roof leak,
damaged gutter/downspout system, damaged coping on top of the wall, plumbing
leak.  If water is not gotten under control, the deterioration will
continue, and the repairs will eventually be damaged. 

Nels Roselund, SE
South San Gabriel, CA
njineer(--nospam--at)att.net
-----Original Message-----
From: Jordan Truesdell, PE [mailto:seaint1(--nospam--at)truesdellengineering.com] 
Sent: Tuesday, March 21, 2006 7:53 AM
To: seaint(--nospam--at)seaint.org
Subject: Condition assessment for old brick walls

I've got a building that is multi-wythe loadbearing brick, but (roughly) 
random portions of the bricks and mortar are in very poor condition.  
There are even a few bricks where you can grab a handful of red sand, 
and "excavate" more than half the brick with a finger. Similar condition 
with some of the mortar joints. The condition is primarily on the inner 
surface - I did not see any deterioration of this significance on the 
exterior. If I had to guess, I'd say 1% to 2% of the bricks, and maybe 
2% to 4% of the mortar joints are no longer capable of supporting any 
type of load.

Any good references or recommendations on when a load bearing brick wall 
is considered "end of life" for a renovation project.

-- 
Jordan


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