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Joint
Filler Profile is Important
The primary
function of MM-80 is to restore the floor surface to
an interruption-free, continuous plane. This is accomplished by
filling the joints flush while protecting joint edges from damage
caused by hard wheels.
Flush Profile=No Impact
Recessed Profile=Impact Points
.........
Obtaining
a flush profile is not as simple as it might seem. Because
floor joints are typically narrow and should be filled full
saw-cut depth, floor joint fillers must be pour grade
liquids. If you fill a joint with almost any liquid, it will
likely settle in the middle and remain higher on the sides.
This is called dishing.
This will happen with any filler and is not caused by
shrinkage of the filler. The problem is compounded, however,
by fillers that generate heat during their cure cycle. Warmer
fluids are thinner than cooler fluids. Thus, the heat
generated by an epoxy during cure may add to the dishing.
MM-80 can be installed with a flush
cured profile by following the procedures described in this
article. The first key to any of the methods is to
effectively seal off any voids at the bottom. Do not use
backer rod. Use Metzger/McGuire's SPAL-PRO ROD or a maximum
of 1/4" of silica sand as described in pages T1 and T3.
The second key is to make
multiple passes. Fill the joint to within 1/2" of the top on the first pass and allow it
to settle for 30-60 minutes. By limiting the amount of MM-80 on your final pass you can finesse
it and make it stay just slightly high (crowned).
OVERFILL
AND SHAVE
Install
MM-80 as previously described,
slightly over filling. Allow MM-80 to go past the gummy state
until it sets into a solid (usually 6-8 hours). If
possible at this time, shave off the excess, since it has
not reached its full hardness and shaving is relatively
easy. Possible shaving tools include well-honed spud
hoes, ice scrapers, tile floor stripping tools, wallpaper
scrapers, putty knives, etc. Having a long-handled tool
adds leverage and is easier on the back.
..................... ...Crowned...........................Shaving.....................Flush Profile
If you cannot shave on
the day of installation, return as soon as possible
afterward. Apply heat to the MM-80 using a hot air gun or torch,
then promptly shave. Do not burn or char the MM-80. (Note: Using an overfill
procedure will leave a slight film on the top of the
concrete, most of which will eventually wear off with
traffic).
TAPED EDGES
Apply tape to both
sides of the joint and then install the MM-80 as previously
described. The thickness of the tape will
partially determine the cured profile. You may
choose to use duct tape, two layers of duct tape
or even foam-backed tape for extra height. Allow
the MM-80 to thoroughly set into
a solid before removing the tape (the excess
above the floor level can be shaved or ground as
described in later paragraphs).
The tape will keep the joint edges neat and
clean.
...............
Before
Filling.....................After
Filling.........
The ideal
profile for cured MM-80
is perfectly flush with the floor, thereby
re-establishing a smooth, interruption-free
surface. Sometimes the MM-80
cures low and the vulnerable edges
become impact points for hard wheels.
Corrective steps should be taken if the MM-80
is deemed too low.
WHAT
CAUSES LOW FILLING
MM-80, like any self-leveling
filler, can cure too low despite having been
applied flush. There are several possible causes
and all are aggravated by the fact that epoxies
generate heat as they cure. Liquids become
thinner when they are warm. An example is syrup
from the refrigerator versus syrup left on the
table.
The most likely causes of low
MM-80
include:
A. During the mixing
process, MM-80 may entrap air
bubbles. Eventually the bubbles rise and the MM-80 runs down to fill in
the void.
B. The shrinkage crack at
the bottom of a joint may not be sealed off. Upon
warming, the MM-80 thins and flows out
through the crack. We suggest using the
Metzger/McGuire Spal-Pro Rod at the bottom
of saw-cut control joints to prevent run-through.
C. The MM-80 was applied high but
was later "tooled" flush while still
liquid. A flush fill will often dish
out (become
concave)
when the heat generation occurs.
D. MM-80 was installed in a single
pass method, not allowing for settlement, or
was not over-filled in a two-pass method
WHEN
IS A JOINT FILLED TOO LOW
There is no
single answer to what is an acceptable profile.
The answer will vary with anticipated traffic
frequency, loading, vehicle wheel size, and owner
or A/E criteria. Generally, the main focus will
be on whether the MM-80 prevents wheel impact
to the joint edge. An impact test with the type
of vehicle to be used in the facility is usually
a valid method of determination.
HOW
TO CORRECT LOW JOINT FILLING
The only
acceptable method of filling joints deemed too
low is to redo a minimum of the top 1/2". This is accomplished by
first saw-cutting out 1/2" minimum of MM-80.
A circular
saw and typical steel blade is usually adequate.
As you cut, be sure the blade cleans any residue
off the side walls. Refill with MM-80, overfilling slightly.
Return when hard-to-the-touch and shave off flush
with razor or similar tool.
HOW NOT TO REPAIR A LOW JOINT
The
application of a thin "cap bead" of MM-80 for low joints
is not acceptable. MM-80, like many epoxies, does
not adhere well to itself. A cap bead will become
dislodged soon after the onset of traffic. To be
durable, a corrective application of additional MM-80 must have a minimum 1/2" vertical bond contact
with the concrete.
 
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