Building Management Hawaii April/May - (Page 14)
3 Steps For A Solid Spalling Job
How to prevent premature failure of concrete repairs.
By Sean Dunham
RestoRation
A
ll too often, concrete repairs
fail quicker than they should.
Have you ever noticed that the areas
you repaired five years ago are
once again a key problem for your
building? While concrete repair
and steel reinforcing construction
are still evolving sciences, there are
some simple steps that you and your
contractor can take to minimize
recurring problems.
As part of the repair process,
deteriorated concrete is removed and
create a void that needs to be filled
with new concrete. An uninformed
or inexperienced repairer might be
inclined to use the latest and greatest,
off-the-shelf mortar promising “no
cracking,” “flows like water” and
“easy to finish.” However, what
is being overlooked is that this
particular “easy solution” might not
be compatible with the adjacent older
concrete. It is important to keep in
mind that all concrete—depending
on its composition—contracts and
expands at different rates when it’s
exposed to heat and moisture ... even
the concrete mix that promises no
cracks will do so over time. And,
when it does crack, it will do so all
along the perimeter where the newer
concrete abuts against the older
concrete. The cracks will allow water
to penetrate to the rebar, causing the
process of deterioration to start again.
An equally critical concern is that the
chemical electrical process that causes
steel to rust can actually be accelerated by
CRACKS
a new repair patch. A new patch typically
has higher alkalinity compared to the
surrounding area. The higher alkalinity
will actually create a cathode and push
electrical current into the surrounding
rebar. This process, in turn, produces
an anode, causing rust to start. This
phenomenon is known as the “ring
effect,” whereby the concrete surrounding
the new patch starts to deteriorate much
quicker than other areas.
At this point, you’re undoubtedly
wondering how to avoid these
problems. There are several easy
steps you can take either during the
contractor bidding or pre-selection
interviewing process.
• First, select a licensed contractor with
the necessary expertise and track
record to capitalize on their knowledge.
• Second, pick the right concrete
aggregate mix and top coating.
Confirm with your contractor that
the proposed aggregate mix ratio
closely mimics the material adjacent
Cost/Sq Ft
Effective
Reapply
Membrane
$6-$8
100%
> 5-7 yrs
Overlay
$12-15
95%
> 15 yrs
Sealer
$2.50
85-90%
> 3-5 yrs
Seal Cracks
$6-7/lin ft
Local
April - May 2013
BMH
REBAR
CATHODE
COMPARISON OF
WATERPROOFING OPTIONS
14
CORROSION
CURRENT FLOW
> 5 yrs
to the intended patch area. Also
confirm with your contractor that
the material meets the industry
standards for your particular
application: a) lack of shrinkage;
b) elasticity; c) proper thermal
coefficient; and d) tensile strength.
Note, there is no need for greater
compressive strength of the patch
relative to the adjacent material.
For example, an 8,000 psi patch is
unnecessary when the rest of the
building is 3,000 psi.
• Third, select a coating material
(painting or waterproofing with
membranes) that can bridge hairline
cracks. This coating will slow down
the process of water and calcium
ion intrusion. Without a protective
coating, the reinforcing steel will
corrode and cause hairline cracks
to expand. While this approach
may be ideal, it may not always be
affordable for a large repair area. In
this type of situation, another option
is to saw-cut a groove along the
perimeter of the repair. This groove
is then filled with sealant that
prevents water from entering where
cracks may occur.
Sean Dunham of
Kawika’s Painting Inc.
graduated from the
University of Denver in
2010 with a degree in
accounting and a minor in
construction management.
He helps Kawika’s with its
bookkeeping, estimating
and project management.
www.buildingmanagementhawaii.com
http://www.buildingmanagementhawaii.com
Table of Contents for the Digital Edition of Building Management Hawaii April/May
Lifts: Elevators & Escalators
Service Providers Leverage Cutting-Edge Technology
Time To Modernize?
Ready To Switch Gears?
Concrete: Restoration & Repairs
When To Test For Lead
3 Steps For A Solid Spalling Job
Deep Secrets
Phase The Work
Concrete Restoration
Tips On How To Reduce Spalling On Newer Buildings
The Difference Between Repair & Restoration
Insurance
Equipment Breakdown Insurance
High-rise Hotspot
EDITORIAL
Toolbox Talk: How to choose the correct ladder for the job.
Industry News and Movers & Shakers
On Site: Saving Staff
Building Management Hawaii April/May
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