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Concrete Floors in Existing
Industrial Buildings...
Asset or Liability
By Steve Metzger
Before you negotiate your next purchase or lease of an industrial
building, take a hard look at the condition of the floor. It could save your company
headaches and money.
The decision to purchase or lease an existing industrial building is often motivated by
time. The building is needed now, or perhaps yesterday. A check-off list is developed and
the clock starts running. A building of the right square footage in the right location is
identified. The layout is good, clear height okay, number of dock doors are okay, no sign
of roof problems, electric service is adequate, etc., etc. But before you sign those
papers, I suggest you take a good hard look at the main thing you are really buying or
leasing . . .
the interior concrete floor.
What is a Floor?
The floor of an industrial building is, in actuality, your company's work surface; and in
a sense is not unlike your desk is to you. If the surface of either is smooth and
interruption-free, productivity is enhanced. If the surface is rough, weakened, or marred
by cracks or joints, productivity suffers. Buying a facility without carefully evaluating
the floor is like buying a desk without looking under the desk pad.
Years ago it could be said that "a floor is a floor". This is no longer true. In
the past twenty years, material handling vehicles (MHVs) have become more sophisticated,
faster, and able to move heavier loads. Vehicles may be controlled by computer or wire
guidance systems. MHVs, SKUs, bar codes, computer designed rack layout, and operator
certification are all part of a system. The concrete floor must be viewed as an integral
part of that system if optimum productivity, and thus profit, are to be realized.
Floor-Effects
How can a poor quality floor affect normal industrial operations? If we define a poor
quality floor as one that has open cracks, broken joint edges, and surface delamination,
the effects can include:
Vibratory damage to MHV parts and connections
Accelerated wheel wear and replacement
Downtime to replace worn wheels
Operator slowdowns for defects
Detours to avoid paths with defects
Increased housekeeping costs
Load tipping if defects are severe
Reduced employee morale
USDA/FDA/OSHA citations
Downtime for eventual repairs
Your company cannot afford a bad floor because a bad floor affects the bottom line of your
operations. It simply makes sense to purchase or lease a facility that has a better floor.
At the very least, it is wise to be aware of the deficiencies in the subject floor; know
how much they will cost to correct; and correct them before you take occupancy (or before
you renew your lease).
A Case History
Let's take as an example a recent tilt-up project I became involved in on behalf of one of
our corporate clients. The building was a new building near Los Angeles, 125,000 square
feet in size, and the lease terms were very favorable to our client. The floor looked
fine, but this owner had been stung on a previously leased distribution center and asked
me to perform an "informal" inspection. From the doorway the floor looked good,
but as I walked through I noticed the construction joints were averaging 3/8" wide
with some occasionally reaching 1/2". I also kept encountering joints where one side
of the joint was just slightly higher than the opposite side. That slight difference in
height may not mean much to most people but it can mean a lot of trouble to an MHV and its
operator. The column diamonds were 1/4" to 1/2" below the floor level, appearing
to have settled. I concluded that the slab was suffering severe "curl" and
excessive shrinkage. The question was how serious were the consequences.
Slab Edge Curl
It can safely be said that all concrete curls and all concrete shrinks. What counts is the
degree of each.
Slabs are exposed to the air on top and, thus, dry out faster on top. As with common mud
that dries out, the edges curl upward and slightly backward. If the curl is minor, it will
have no effect on the durability of the floor. If the curl is severe, it can mean that one
slab segment ends up higher than the adjacent one. It can also result in the bottom of the
slab lifting up and off the subgrade, thus being in a cantilevered position. Too much of a
load and this suspended section will break off.
Edge curl is most commonly found at pour ends (construction joints) and especially at
corners; thus, the apparently settled column diamond had not really settled. The slab end
had, in fact, curled and risen. In the case of the subject floor there was also evidence
of considerable curl at the intermediate
saw-cut control joints. This was not a good sign. Curl is a result of significant loss of
slab moisture and moisture loss is usually not that great between construction joints.
Slab Shrinkage is Normal
Shrinkage of the mass of a slab is always expected since all concrete mixes contain excess
water for workability. This water should evaporate slowly over a period of one to two
years. Shrinkage occurs as moisture is lost. A general rule for a "reasonable"
mix is that a 5" to 6" slab will shrink 1/8" in 20 feet. This means a
construction joint that was originally poured tight might reasonably be expected to open
to 1/8", perhaps to 3/16".
The construction joints in this slab were 3/8" to 1/2", double what one would
normally expect. In addition, the 1/8" diamond blade-cut control joints halfway
between the construction joints also opened and now averaged 1/4" plus. My initial
guess was that the mix either contained too much water or an additive was overused. It
turned out both were good guesses.
Joints and Load-Transfer
One desirable effect of any joint is to have load-transfer. In other words, we want the
entire floor to act in unison under traffic despite the fact we pour it in sections and
further divide it by cutting or forming control joints. (Control joints direct the
expected shrinkage cracks in straight lines.)
Ideally, as an MHV crosses a joint, the two slab segments should work together. If one
segment deflects under load while the other stays high, edge damage occurs due to
hard-wheel impact. Load transfer is usually accomplished by design (dowels at construction
joints) or by aggregate interlock.
The inspected slab had no dowels at the construction joints and the sawn control joints
had opened too wide to have any effective aggregate interlock. The result was that each
14' ´ 14' slab section moved independently. To verify this we borrowed a half-loaded MHV
from a company across the street. The vehicle confirmed my fears. The floor looked like a
teeter-totter as the vehicle drove across.
Cure for Lack of Load-Transfer
There are few cures for slabs with no load transfer, and none of the cures are
inexpensive. We opted to explore a low-to-middle cost procedure which included:
1. Pressure-grout under each joint to reduce the up-down movement
2. Fill the joints full depth with a
non-structural, semi-rigid epoxy
3. Grind the worst curled joints down to an acceptable level
4. Apply a liquid hardener to the edges where grinding was performed.
We solicited bids from two local contractors with whose work I was familiar. The bids came
in at $53,000 and $59,000. The owner/developer refused to pay for the corrections and my
client wisely backed off. He promptly found another facility nearby with a durable floor.
The facility with the problems? I hope you didn't lease or buy it. If you did, your
operations people soon knew they had a big problem on their hands.
All Floors Are Not Equal
All floors are obviously not created equal and it is not at all difficult to get stuck
with one that can be a long-term headache. How can you avoid getting stuck? There is no
sure, 100% way to avoid problem floors, but you can minimize your risks.
First, learn about floors through books or seminars; bring in your corporate engineers or
retain a floor consultant before you structure the deal.
Second, be aware that many existing facilities are built by non-contractors who hire
second-rate contractors with only a low bid as their qualifications. I don't mean that to
be a slap at developers, but it can be the case, especially with 'spec' buildings.
Third, be cautious in areas where floor construction is known to be marginal. Other
corporate real estate professionals can prove to be helpful in this subject.
Red Flags
There are far too many warning signs to list in this brief article, but the following is a
sampling of red flags (along with those cited in my case history):
1. Broken corners.
When the corners of slab sections have broken off, it can be a sign of severe edge curl.
2. Delamination.
Be very cautious if you find shallow pieces of the surface coming off. It can mean that
the entire surface is weak due to poor finishing.
3. Replaced concrete.
If various areas have already been replaced, it is probably due to deficiencies that are
prevalent throughout the building.
4. Metal joints.
Construction joints are often formed with left-in-place metal keyways. These joints almost
always deteriorate with hard-wheeled traffic and the metal "chews up" wheels.
Conclusion
There is a direct relationship between the quality of an industrial floor and the profit
of the operations that function on it. Consider the quality of the floor on all future
industrial real estate decisions. Do not forget to evaluate the floors in your presently
leased facilities that are up for renewal. (Ask any MHV operator if there are significant
floor defects, he'll know.)
Don't let your floors cost you money... let them help your company make money.
Copyright 2001 Metzger/McGuire
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