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RE: Crumbling concrete

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Jordan,

I've noticed that the presence of efflorescence is most reliably found in
unused spaces such as crawl spaces under houses, and in little-used
basements.  The elements tend to wash or blow it away from exterior
locations, and busy places are often kept clean.

The elements of the roof drain system appear to be of modern components.  It
may be that they were installed because the basement was getting wet.  If
that can be confirmed by the owner, it may be that the source of the
moisture has been mitigated, and the wall surfaces can now be safely
repaired.  If that is the case, thorough removal of the damaged material and
trowel-applied non-shrink stucco [as can be made with CTS Eisenwall cement]
can now be applied.

Another source of moisture near an old house that I forgot to mention is
sometimes a change of grades adjacent to the house.  Erosion can remove soil
that used to provide slope away from the house, or moisture-related
consolidation can cause settlement, resulting in slopes toward the house. A
discussion with the owner about the 40 years of the house's history that he
knows about may help establish what has happened to cause the deterioration.
A house that went for 60 years before moisture related problems developed
would seem to have been built well enough, but subsequently, something has
been done to breach its original moisture protection.  Be a detective.


Nels Roselund, SE
South San Gabriel, CA
njineer(--nospam--at)att.net

-----Original Message-----
From: Jordan Truesdell, PE [mailto:seaint(--nospam--at)truesdellengineering.com] 
Sent: Thursday, December 23, 2004 10:26 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Crumbling concrete

I actually had to look back at the photos when you mentioned efflorescence, 
as I saw none while I was on site.  I think you're seeing false color as a 
result of the on-camera flash combined with the variation in wall texture 
in the outdoor shot.  Efflorescence is a common problem in my area, so I'm 
familiar with what it usually looks like.  I looked for the presence of 
obvious crystallization, but could find nothing by eye. The white in the 
last photo looked more like a spilled/cleaned up mess than an evaporate 
when I was on site.

One of the intriguing aspects is that this is occurring on a wall which is 
both entirely above grade and under a covered porch on the exterior, as 
well as the partially below grade walls.  There's no telling what type of 
foundation is below the walls - they may have been placed without a footing.
The wall does get moisture, and there is noticable water in the basement 
during the one or two heaviest rains each year. The back of the lot slopes 
up probably 10-12 feet in 40-50 feet of run, and part of the basement is on 
rock (1/2 basement, 1/2 crawlspace), so parts are going to see wetness 
every big event simply due to volume.

I took a sample, and once I research on the possible causes, will send it 
off to my local lab to tell me what is in it.



At 08:31 AM 12/23/2004 -0800, you wrote:
>Jordan,
>
>This looks like deterioration due to moisture penetration from the
exterior.
>Look for a not-original moisture source adjacent to the house.  Often it is
>a planter that was added adjacent to the house [that does not seem to be
the
>case here], or a removed roof-gutter-and-downspout system [though I've seen
>this a number of times -- the old gutters start to leak and, rather than
>repair or replace them, the decision is made to just remove them and let
the
>water fall from the eaves to the ground next to the house -- that may not
be
>the case here since there seems to be a downspout-to-drain-pipe system next
>to the house].  However, since there is a lot of damage right where two of
>the drain pipes enters the ground, perhaps the drain system discharges
under
>ground next to the house instead of carrying the water away.
>
>It works something like this.  Water from some source enters the wall and
>migrates through it.  Salts dissolved into the moisture from the soil, or
>from the concrete as the water passes through it, crystallize when the
>moisture evaporates into the air in the basement or above grade.  The
>crystals form just inside the surface of sound concrete; the crystals grow,
>expanding and breaking up the concrete matrix.  The damage is progressive,
>working its way into the wall, under the damaged surface, always acting at
>the surface of sound concrete.  If you scrape away an area of the damaged
>surface, you will eventually come to sound concrete. An indication that
what
>I've described may actually be the cause would be the presence of
>efflorescence [visible accumulations of salt deposits and crystals] on wall
>and floor surfaces near the damage.  That may be what is visible in the
last
>photo and perhaps in the second photo.  Also, since moisture does not
>evaporate below grade, the damage probably does not occur more that a few
>inches below grade.
>
>Nels Roselund, SE
>South San Gabriel, CA
>njineer(--nospam--at)att.net
>
>-----Original Message-----
>From: Jordan Truesdell, PE [mailto:seaint(--nospam--at)truesdellengineering.com]
>Sent: Thursday, December 23, 2004 6:19 AM
>To: seaint(--nospam--at)seaint.org
>Subject: Crumbling concrete
>
>I'm curious what would cause older concrete walls to crumble into a
>lightweight, easily-friable condition.
>
>Here's my story:
>
>I just went by a 100+/- year old residence yesterday and saw the most
>amazing concrete wall deterioration I've ever seen.  Portions of this
>mostly-above-ground basement wall (I'm going to say 30-50%) were friable to
>the touch, and easily (literally fell apart) crumbled in my hand.  In the
>soft areas, a masonry bit advanced without significant resistance until it
>hit a large piece of aggregate, usually about 1.5 to 2" into the 9" thick
>wall. My only time reference is that - according to the owner - it wasn't
>present in the 60s when they bought the place.
>
>There is significant evidence that some organics were included in the mix,
>along with sand and round river rocks.  You can see the diagonal striations
>of segregation from where the concrete batch placement started at the
>corners and flowed down the walls to its final resting place.  I'm guessing
>that casual water intrusion has slowly decayed the organics to the point
>that they have partially disintegrated reducing the strength, with the
>remaining organics moisture cycling to break what was left.  There was no
>obvious sign of chemical residue on the surface of the wall.
>
>Interestingly, there is no sign of macro-deterioration of the structure
>(yet). No settlement or stress cracks, even where the unbalanced backfill
>is close to 5 feet.  Nonetheless, the walls are going to have to be
>replaced.
>
>I'm curious what might be happening, and if there are any tests that might
>be recommended to determine the cause of the damage.  I'm doing this as a
>side research (unbillable) for future reference, as the current owner just
>wants to know how to fix the problem (replace the walls), and the value of
>the house is only about $120k-$130 without the wall issue, and currently
>has no historic significance.
>
>If you're curious, there are some photos here:
>
>http://www.truesdellengineering.com/1125/index.html
>
>Thanks, in advance, for any thoughts/suggestions you folks might have,
>
>Jordan
>
>
>
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