Approximately
80% of the
cracks we see
in residential
structures are
horizontal,
vertical, or
diagonal. A
large number
are minor and
do not require
action.
Horizontal
Cracks
Horizontal
cracks are
usually
structurally
related.
However, their
significance
depends on
whether there
is lateral
movement and,
if so, how
much.
If a
wall has moved
1/3 of its
thickness out
of plumb, it is
in imminent
danger of
falling. If it
has not moved,
or if the
movement is
less than 1/3
of its
thickness, the
wall can
probably be
reinforced.
Vertical
Cracks
Vertical
or nearly
vertical cracks
are only
structurally
related when
there is
lateral
movement (i.e.,
bow or shear).
This assumes
the crack is
consistent in
width from top
to bottom. In
most cases,
vertical cracks
are hairline or
not much wider
and are caused
by normal
shrinkage or
contraction.
Expansion
and contraction
are normal for
building
materials. The
more rigid the
material is,
the more likely
a crack will
develop. Porous
or less dense
materials will
be flexible and
less likely to
crack. Vertical
cracks in a
wall with a
vertical bow or
with sheared
wall planes are
structurally
related.
Contraction
cracks are
hardly ever a
structural
concern.
Diagonal
Cracks
Diagonal
wall cracks,
which break
through the
building
material, are
almost always
structurally
related. Step
cracks in a
block wall that
only crack at
the mortar
joints and not
through the
block is
typically a
structural
problem, unless
lateral
movement is
present.
When the
bearing or
foundation
under a wall is
not adequate,
the wall will
settle or sink
at the weak
area. The
adjacent wall
structures that
are adequately
supported will
resist this
movement. This
situation will
cause diagonal
cracking.
To
determine the
cause or the
source of a
diagonal crack,
draw a line
perpendicular
to the crack
down from the
approximate
center of the
crack. Once you
locate and
understand the
source of the
crack, proper
corrections
will be
relatively easy
to determine.
Cracks
in ceramic tile
floors
Cracks
in ceramic tile
floors are
generally due
to two things:
1.
Materials of
different
densities that
expand and
contract at
different
rates. (e.g.,
ceramic tile
vs. wood).
2.
Floor systems
not stiff
enough to
receive a
ceramic tile
floor.
If
the strength of
the floor is
adequate, using
an additive in
the grout
allows the
ceramic system
to flex with
the wood floor
system and
eliminates the
typical
differential
expansion and
contraction of
the materials.
Cracks
in plaster
ceilings
Cracks
in plaster
ceilings are
generally due
to one of two
reasons:
1.
Over the years,
gravity will
cause plaster
to crack.
Typically,
cracks develop
in larger
ceilings in the
direction of
the longer
dimension at
approximately
30 to 40 years.
Cracks develop
perpendicular
to the first
cracks when the
ceiling is
approximately
50 to 60 years
old. Sections
of the ceiling
loosen in
approximately
70 to 90 years
and repair or
replacement is
then necessary.
2.
When the frame
structure above
a ceiling is
not stiff
enough to keep
the plaster
from cracking,
premature
cracks are
inevitable.
Excessive
weight or
bouncing can
cause floors to
flex, and cause
plaster on the
ceiling to
crack.
There
are various
solutions to
these problems.
These solutions
are influenced
by such things
as thickness,
height, and
span of the
wall; source of
the problem and
available
space.
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