When was AMCOS Geotechnical (AG) founded?
ANS: Founded in 1978 by Nils
Jansma, AG offered a specialized service that was largely
restricted to the Geotechnical community. However, in 1988, AG
opened up its services to the general public and has been
successfully serving in that regard ever since.
What does AMCOS
do? ANS: AG provides a top-notch
quick, dependable solution to the problem of cracked slabs or
foundations, great customer support, and prices that can't be
beat! Generally, even the most serious problems can be fully
repaired within one week.
What is the most commonly asked question
about a cracked or broken slab? ANS:
"IS MY HOUSE SAFE TO LIVE IN?" The answer generally, under most
circumstances, is “YES,"
Do these questions and answers apply to
all concrete foundations and slabs?
ANS: No! You have to distinguish between “above-grade” and
“slab-on-grade” foundations. Most of the problems or damage
associated with cracked or broken foundations involve
slab-on-grade structures.
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What is the
difference between an “above-grade” foundation and a
“slab-on-grade” foundation? ANS:
An “above-grade” foundation is used to support a wood floor and
wall system while a typical “slab-on-grade” is made entirely of
concrete that includes a “perimeter” foundation. The wood floor
system generally covers an 18-inch crawl space that requires the
interior part of the house to be supported on regularly spaced
“piers.” The concrete slab-on-grade generally rests directly
on the ground or “grade” and does not include a crawl space. Back
Is a broken
“above-grade” foundation as serious as a broken “slab-on-grade”
foundation? ANS: No! Often,
the wood “floor and wall system” has sufficient strength to
bridge over a broken perimeter foundation. Differential
movement of the broken perimeter foundation is more likely to be
evenly distributed through the wood floor and wall system. This
arrangement often prevents damage from being transmitted from
the broken foundation to the walls above. However, this is not
the case with a slab-on-grade foundation. When differential
movements occur, the wall system above is immediately impacted
and often damaged.
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When is damage to an
“above-grade” foundation considered serious?
ANS: When there is obvious damage to the upper structure that
is clearly associated with the foundation damage. This is
generally due to differential settlements of the structure that
has caused the foundation to break.
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What causes concrete
to break? ANS: There are a
variety of potential causes many of which will be discussed in
more detail in connection with other more specific questions.
However, in general, there are three basic problems that
probably cause most of the serious concrete damage associated
with residential structures. These are concrete shrinkage,
expansive soils (clays), and soil consolidation or settlements.
Often, these work in combination.
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What is generally not
a cause of cracked or broken concrete in the San Diego area?
ANS: Cracks and breaks due to “earthquake” or seismic
activity. Earthquakes intense enough to break slabs and
foundations rarely occur in San Diego county. If a local
structure is damaged by seismic activity, it is probably because
of an already existing weakened condition. Back
I have been told that "all
concrete cracks sooner or later," and so not to worry about it.
Is that true?
ANS: Yes and no or "YO."
More often than not, concrete cracks develop during the "curing" stage due to
"shrinkage." However, there are “cracks” and then there are
“cracks.” Just because they happen due to “shrinkage” does not
mean that they are not “serious.” So whether you should “worry”
about them or not depends upon where they are located and how “bad” they
really are.
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Can cracks due to “concrete shrinkage” be
avoided? ANS: Yes
but it does require a lot of care before, during, and after the concrete
is poured. Aside from unanticipated site conditions probably
the second greatest reason why “concrete curing” causes cracks
is because the slab was not properly reinforced with steel.
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Does reinforcing slabs with steel guarantee
that the concrete will not crack?
ANS: NO. However, if a slab is adequately reinforced, the
cracks that occur will usually not be serious and may not need
to be repaired “structurally.” Usually, properly reinforced
concrete only allows numerous, relatively small harmless cracks to occur
rather than one big one.
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Don’t local codes usually require slabs and
foundations to be reinforced?
ANS: YES for the slab and NO for the foundation. The big
“problem” is that most slab reinforcement has not been properly
placed and so is ineffective. Unless the steel reinforcement is
physically “lifted” to the middle of the slab during the
concrete pour, it will not work. Steel that is walked on by the
installers and allowed to remain at the “bottom” of the slab is
next to “useless.” That is probably why I have never repaired a
slab with properly placed steel reinforcement.
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Why are broken slabs
and foundations a cause for concern?
ANS: The answer is four fold:
A. The damage reduces the value of the house compared to an
undamaged house.
B. Finance companies will generally require that the damage be
fixed by a reputable party before they will offer full
financing.
C. All Sellers are required by law to disclose the damage to a
future buyer. A Prospective Buyer knows that the damage
will have to be fixed sometime in the future to avoid a loss of
resale value. What is saved now will be lost then.
D. The damage to the slab and foundation may actually be a
“symptom” that there are site-problems that could significantly
reduce the over-all value of the property at some time in the
future.
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Is there any good reason why the Damage
should be fixed now rather than later?
ANS: YES. Imagine if you were considering the
purchase of a
house and that you were told it had significant repairs made to the slab or foundation . What would you prefer
to hear as a buyer, a repair
with a 5-year history of no movement or one made recently?
Obviously, the longer a repair proves to be a success the less
concern it becomes. Most finance agencies disregard the
adverse impact of a repair if it has a successful history of at
least three or more years.
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How can I tell if I
have a serious problem? ANS: If you
observe interior or exterior wall and/or ceiling cracks that are
1/8-inch or more, then you can anticipate that your problems may
be serious. If you observe that such damage is accompanied by a
visually evident tilting floor slab, the probability of serious
damage increases significantly.
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Is there any way I can
look at a house and tell if it has a marginally damaged slab or
foundation? ANS:
Yes. If you see cracks longer than 24-inches around
exterior windows and /or
corresponding interior damage along with ceiling cracks, then
that may be an indication of foundation damage.
Additionally, if the exterior foundation is visible, you
generally see vertical cracks of any size in it also.
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What are some of the
symptoms of a house with a significantly damaged slab or
foundation. ANS: Often, you will see
corresponding exterior and interior wall cracks. The house may
or may not have interior ceiling cracks. If the house was built
since 1960, you will likely be able to visually see breaks in
the exterior foundation. If built before 1960, you may see
exterior wall cracks that extend down to the ground elevation.
Often you will see exterior wall cracks around windows that
extend both up and down to the wall edges.
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Can a slab be cracked
and still not have to be repaired? ANS:
Slab cracks that do not go through the exterior foundation often
do not need to be repaired. Generally, they do not completely
penetrate the slab.
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Can a foundation be
cracked and still not have to be repaired?
ANS: Foundation breaks are different from
slab breaks. Whether to repair them or not depends upon
subjective (personal) criteria. If non seismic safety is your
concern, then many foundation cracks do not have to be
repaired. However, such unrepaired foundations may cause the
house to experience up to 100 times more damage during a
significant earthquake. Additionally, normal ground vibrations
cause by air and/or road traffic along with seasonal site
moisture fluctuations may also result in wall and ceiling cracks
that cannot be repaired permanently.
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What damage often
happens to a house because of a broken slab or foundation?
ANS: This depends upon the cause. The
breaks in the slab and foundation act like “hinges.” This means
that the slab and foundation become extremely “flexible.” This
flexibility forces the house frame to help keep the foundation
and slab together. This results in predictable damage in the
form of cracks and breaks to occur to the house frame.
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What is the primary
cause for a slab or foundation to break?
ANS: The primary cause is “normal” concrete shrinkage due to
misplacement of concrete reinforcement. The shrinkage problem
may be made worse by pouring “wet” concrete on a “hot” day.
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After
“concrete shrinkage” what other factors cause concrete to break?
ANS: Generally, there are two other reasons for concrete to
break if not due to normal shrinkage. These would be, expansive
soils and/or settlement of artificial site fills.
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Why
do cracks appear in the walls and ceilings of a house
supported by a broken “slab-on-grade” foundation?
ANS: When a slab-on-grade foundation and slab breaks, the house
slab is divided into multiple sections separated by a measurable
space. This allows the individual pieces of the slab to move
independently (differentially) of one another. The differential
movement of all the slab pieces requires that the upper “house
structure” hold them together during movement episodes.
Movement episodes can be caused by earthquakes, wind buffeting,
vehicular road traffic, sonic booms and other various
“transient” energy sources. Because the house structure was not
designed to hold the slab together, its rigid surfaces crack in
various locations. If the foundation is not repaired, these
upper structure cracks cannot be permanently repaired.
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Why
would a house with broken foundation experience significantly more damage during
an earthquake than a house whose foundation has been properly
repaired?
ANS: During an earthquake, a house foundation is subjected to
both “push” and “shake” forces. As long as the foundation is
not broken, the push and shake forces do not cause major damage
to the upper structure. However, when the foundation is finally
broken by the earthquake, the house foundation is segmented into
separate pieces which begin to move independently of one
another. This independent or more properly called “differential
movement” results in considerable damage to the upper structure
in a very short period of time. Consequently, a house with an
"already-broken" foundation is subjected to “differential
movement” during the entire earthquake period and will likely
experience up to 100 or more times the damage in comparison to a house whose
foundation and slab does not break.
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What is the best way to
repair a broken slab and/or foundation?
ANS: The best way to repair a broken slab and/or foundation is
by having the separate slab pieces bound together with
“structural steel” that equals or exceeds the strength of the
original slab before it was broken.
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What is meant by a
“structural” repair?
ANS: A structural repair must bind the broken slab parts
together in such a way to make it as strong or stronger than
before it was broken.
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What is an “epoxy”
repair? ANS: Epoxy
is a type of very strong glue. An “epoxy repair” is
suppose to glue the two
slab portions together.
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Is an
epoxy repair a “structural” repair? ANS: An epoxy repair is
generally not considered a structural repair for normal
residential construction. This is because the two broken edges
of the slab pieces are usually not completely covered by the
bonding epoxy. Therefore, without exceptional application
techniques, the epoxy repair can never restore
100% of the slabs original strength.
All of the epoxy repairs
examined by AMCOS have only penetrated the crack approximately ˝
inch at most. This amounts to a restoration of
approximately a maximum of 12% of the original strength of the
slab. However, due to poor preparation of the slab edges, it is
estimated that such a repair restores no more than 5% of the
original slab’s strength. Nevertheless, even if credible
proof can be offered of 100% penetration of the applied epoxy,
it is estimated that only 30% of the original strength of an
unbroken concrete slab can be restored under residential placement
conditions.
This deficiency is due to inadequate cleaning
of the full depth of the broken pieces of the concrete slab.
This conclusion can be confirmed by testing. When epoxy
repairs are tested by breaking them apart, the broken surface is
observed to have only a small number of tiny pieces of broken
concrete attached to it. This means that the actual break
occurs mostly in the weaker epoxy-bond zone and not in the
concrete.
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Can I
trust a contractor or Engineer who says that an observed
foundation and/or slab break will not move in the future? ANS:
YES, if he or she will give you a written guarantee.
Without a written guarantee, the answer is an emphatic NO!
A person who will not put their opinion in writing is at best
guessing and at worst, conspiring.
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How can
a contractor or Engineer say with assurance that a broken slab
or foundation will not move in the future? ANS: By repairing
it. Generally, no one can predict the future. However, if a
slab or foundation is properly repaired, one can guarantee that
the repair will not move again within a specified period of
time. If the repaired break does “reactivate” then it should be
repaired again without charge. That is what a guarantee should
provide.
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Are all
guarantees the same? ANS: No. A guarantee is only good for
the items it covers. A good guarantee covers the repaired crack
itself which is generally what is expected. However, other
guarantees are for “workmanship” or “products.” These are of no
use if the repair fails. One should carefully examine a
guarantee and make sure that it is not limited to the
“workmanship” employed or the “products” used.
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If an
Engineering report accompanies a repair, does that mean it has
been properly done? ANS: YES, most of the time. However, some
engineering reports are carefully worded to transfer
responsibility for selecting the repair to the Real Estate Agent
or the Seller. If a choice of solutions are given by the Engineer
that have a significant price range, probably only the most
expensive repair carries a guarantee. Should the Agent or
Seller select a less expensive repair solution, they might find
that they have voided the warranty. These type reports may not
give the expected protection and should be used with caution.
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Is it necessary to remove carpet/tile in
order to perform an inspection of a slab-on-grade foundation?
ANS:
Not necessarily. If the foundation is
visible outside, we generally can discover any serious breaks by
just walking around the house. Or, sometimes, when there is
obvious interior wall or ceiling cracks that might indicate a
foundation break, we will use a sub-carpet probe to locate the
edges of a cracked or broken slab. However, if you are serious
about buying a house, the very best way to find all the
foundation damage is to loosen the edges of the carpeting
adjacent to the exterior walls and expose about 12 inches of the
concrete slab. Any such work is the responsibility of
others and should be done in advance of inspections performed by
AMCOS.
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