We recently purchased a house in (earthquake prone) Southern
California. The property is surrounded by a 6' cinder block wall,
built around the same time the house was (1965). It has become apparent
to me that the wall was constructed without rebar or concrete
reinforcement and, in a few places a couple courses of block have
fallen off. My question is if it is possible to retro-fit the wall to
make it secure. In other words, can the decorative course of brick at
the top be removed, rebar and concrete added to stabilize the wall or,
should the whole thing be removed and rebuilt?
Cinder block or 4"/ 6" concrete fence block?
Fence block is "keyed" on the ends and is only mortared between courses.
Where I live non-earth moving zone there is supposed to be a ~4 inch wire
lattice installed every other course. Helps keep it together. Then there are
"piers" every ~13' or so which are filled with concrete and rebared to the
If it is as I describe yes it can be repaired.
I live in earthquake prone Northern California.
I don't think you can retrofit the wall, there's too many things you'd
need to do. Just stuffing rebar down the holes and filling them with
concrete may make the wall stronger, but what's the foundation
underneath? I was within 5 miles of the epicenter of Loma Prieta quake
in '89 and I remember a bunch of cinderblock walls coming down in the
quake. I'd remove it and rebuild it with sufficient footings under
some sufficient vertical support.
Oh wait, idea. You could possibly bolt some 3-4" dia pipes to it every
6 feet or so. This is just a guess. Every 6 feet, dig a 2 foot hole,
put the pipe in, run long bolts thru the pipe, thru the cinderblock,
into a big steel washer/plate on the other side. Probably use about 4
bolts along the length of the pipe. Then fill the hole with concrete.
Realistically, since I don't think there's an easy fix for this, and
since you are probably right that, after a quake, it may come down.
If you're going to put some sweat into this job, get a civil engineer
to take a look at it and give you some good advice. It would cost you
a modest amount, but at least you'd know you were doing the right
thing. Otherwise, you may do a bunch of 'work' to make it good in your
own sight, but the thing would still come down. Look what happened to
the Cypress structure in Oakland during Loma Prieta, and that even had
engineers design it. Bottom line, engineers know quite a bit more now
than they did then and that knowledge will help you out in this
Obviously you need a prof engineer to look at the wall. If you have to
replace it you might consider an interlocking wall instead. Anchor Block is
one brand. Some of their high end materials look like stone. I just had one
put up (a retaining wall) and it looks great. But it has to be done right.
On 15 Feb 2006 12:59:08 -0800, firstname.lastname@example.org wrote:
Is your objective to prevent quake-damage to the wall, or
just to keep it from falling on anyone when it is damaged?
If its regualr concrete-masonry units, then yes, you
can saw (or bash) the top row off and insert vertical rod,
which should keep it from spitting out individual blocks
on peoples heads. If the wall is actually necessary
because of the people-environment, this would be a good
time to retro-fit the wiring for an intrusion-detection
systems. Another alternative would be to cover
one or both faces with hardware cloth and parge it,
which would also prevent it from spitting out individual
chunks of masonry. I can't think of anything short
of buttresses that would keep the whole thing from
coming down all together in a major quake, but I'm
not an expert.
Me again from earthquake prone northern california.
What I notice the developers putting up all over the place here are the
precast concrete wall. Every (6 to 30 feet or so, depending on the
terrain) They drilll a hole in the dirt, put a footing with about a 2
1/2 inch square I beam sticking up about 2 feet. A crane puts a
precast column on it, then a crane puts a precast panel on either side
of it, then another column is put on the other end of the panel. It
seems to be a lot more robust than the cheezy precast walls they put up
about 10-20 years ago that were made out of man-handleable size pieces
of concrete. Those seemed to break all the time.
We are in a pretty benign area so, the purpose of the wall is to
separate our yard from the people next door.
I have thought of doing as you say - taking off the top row, adding
rebar and cement to make the wall solid. When 'the big one' comes, I
reckon that means the whole wall falls down rather than individual
To keep it quake proof, he must drive 10 inch steel well casings down
to the core of the earth, and place them every six feet along the
wall. Then these casings must be filled with concrete and welded
together about 2 feet below the surface of the ground, with sleeves
that allow for flexation during a quake. Attached to these casings
and the welded frame must be thick rubber shock mounts between the
casings and a heavy steel welded frame. Inside each frame the blocks
are placed with rebar in each course. This should make a wall that
will remain stable during a quake, but may cost several hundred
million dollars to construct.
The other solution is a picket fence. The worst thing that can happen
to a picket fence during a quake is a few boards falling off, or a
section landing on someone's toes.
Brilliant! except for the fact that, in addition to earthquakes,
Southern California is also subject to wildfires. I think that a picket
fence might provide a source of kindling in those situations and might
not be as benign a soloution as you think.
I guess my only option is to move.
Was it me, I'd probably get rid of the wall.
Are you trying to just MARK the boundary,
or do you need a privacy barrier? If the
former, replace the concrete monstrosity with
a (fake) wrought iron fence. Or just
resolve to stay more than 6 feet away from
it during earthquakes.
You could put in a boxwood hedge, and
set up the irrigation lines to double as
fire suppression systems.
If you've got the yard-room, you
could put in the previously mentioned
butresses, which are architecturally
far more interesting than a featureless
block wall, but hard to mow around.
Do you own both sides of the wall, or
is it right on the property line?
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