Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CEMENT FINIS~IER'S ~NEE BOARD
BACKGROUNG OF THE INVENTION
FIEID OF THE INVENTION:
This invention relates to supports for workmen who must
perform their work in a constant kneeling position. The support
must perform the functions of (1) protecting the knees of the
user over a sustained period of use (2) distribute the workman's
weight over an increased area and (3) serve to protect or guard
the surFace being worked. More particularly, the present
invention relates to a knee board or kneeling board especially
adapted for use in finishing cement or concrete floors and slabs.
The work of smoothing and Finishin~ the surface of a concrete
slab is, of course, done prior to hardening of the cement and
while the cement is still green and wet or moist on the surface.
This invention is directed to a single board which accommodates
both knees and both toes allowing the workman to work with
finishing trowels in a full kneeling position without the
necessity o-F strap-on devices for the knees or legs.
DESCRIPTION OF THE PRIOR ART:
In the construction ;ndustrY, concrete slabs are
commonly finished by hand troweling. The work is usually done by
assuming a full kneeling position and using one or two hand
krowels as the workman moves rearwardly across the surface of the
uncured cement surface. Working under thsse conditions requires
some form of protection For the workman's knees both in terms of
flotation or support on the surface oF the soft concrete and From
the standpoint of cushioning or easing the pressure on the
workman's knees over sustained periods of time. In
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addition, the support apparatus must also be such as to avoid asmuch damage as possible to the soft sur~ace of the uncured
cement. Since ~he workman must traverse the slab, whatever knee
protection and support is utilized must also move with the work-
man acro~s the ~oft surface. One common form of protection for
floor finisher's knees which has been used in the past, with
many attendant problems, are devices which fasten to the user's
knees or legs with straps, belts or the like which hold the knee
pad to the leg in the kneeling position. The U. S. patent to
Russell No. 2,476,565, issued July l9, 1949 and the U.S. patent
to Zirves No. 3,346,877 are examples of such types of knee or
leg engaging pads. The patent to Zirves, although not directed
specifically to cement finishing, illustrates a typical clip-on
knee pad. The devices of both of these patents are necessarily
flexible so as to be worn or wrapped around the knee and thus do
not function in a satisfactory manner to support the workman on
a soft surface such as wet concrete. Soft pliable knee pads of
this type are thus not generally acceptable for cement
finishing. In addition, this type of knee pad does not make
provision for supporting the user's toes while in a kneeling
position which is a problem on a wet soft surface. Attempts
have been made to combine the soft cushion type knee protectors
such as di.~cussed above with hard surface flotation boards which
accommodate both the knee and the toe of each individual leg of
the user. Examples of this type of strap on knee protector~ are
illustrated in the U.S. patent to Emmett No. 2,719,576, issued
October 4, 1955 and the U.S. patent to Ramon No.3,084,458,
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issued April 9, 1963. These two types of devices are similar in
that a soft or pliable resilient cushion member is mounted on
the top of a hard surface flotation board. The board is usually
formed from wood or other hard smooth surface material. These
two latter patents have the same drawbacks as previously de-
scribed in that the use of straps which engage the knee or the
calf of the leg become extremely uncomfortable over long periods
of tlme when in the kneeling position. These devices are also
extremely cumbersome when considering that a ~eparate device i8
utilized for each leg and must be dragged across the soft wet
surface as the finisher moves backwardly. ~ further example of
the individual kneeling board is disclosed in the U.S. patent to
Hammond No. 4,346,784, issued August 31, 1982. This type of
individual knee and toe board also combines a hard surface
wooden board or the like with a cushion surface on the upper
side. Although the prior art contains examples of knee pads and
floor ~ats in general such as the U.S patent to Rundell No.
830,103, issued September 4, 1906 and the U.S. patent to Solin
NoO 3,3'9,273 issued May 16, 196t, such soft and pliable pads do
not offer a solution to the problems inherent to knee protection
and soft surface cement finishing of the type under
consideration.
AB a re6ult o~ the difficulties and inadequacie~ of
prior art support devices and knee protectors available to the
cement finisher, it i8 still by far the most common practice to
simply utilize a piece of plywood, oftentimes w$th no knee
padding or protection whatsoever to ease the pressure on the
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workman's knees. The presence of straps or buckles about the
knee and calf when used have the effect of limiting blood circu-
lation over long periods of kneeling. Usually ~wo such plywood
boards are utilized wlth the workman moving from one board back-
wardly to another, moving the previously used board to a new
position and thus incrementally moving across the wet concrete
surface from one board to the other~ This common practice re-
sults in severe knee injury when practiced over an extended
number of years. The result is a very slow and progre6sive
disabling of the user's knees and attendant pain and discomfort.
In addition~ this process of hard board placement and movement
across the soft concrete surface entails additional work for the
craftsman since each time the board is moved, dragged or lifted
off of the uncured cement surface a considerable amount of
cleanup of that area must take place. This is augmented by the
fact that the wood surface absorbs moisture and the concrete
adheres to it. The present practice of hard knee board use with
all of its problems is evidence of the inadequacies or the un-
desirablilit1es of known protection devices.
S UMMARY OF TH B I NVENT I ON
The present invention provides a novel knee board par-
tlcularly adapted for cement finishers which overcomes the dif-
ficulties and drawbacks experienced with prior art devices. The
present invention eliminates any need for knee strap6, toe
straps and/or independent apparatus for separately attaching to
and moving with each leg of the workman. The knee board of the
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-~resent invention co~bines the functions of wei~ht spreading
3upport or flotation and knee protection ~hich in the past has
required separate hard boards and soft cushion elements. The
present invention utilizes a single member which is extremely
stiff and is not bendable so as to be capable o-f spreading the
weight of the user over a significant area and at the same time
provide a requisite deformation and cushioning at the knee
contacting surface to protect the user's knees from injury. The
knee board of the present invention is extremely buoyant and may
be conveniently moved about on the wet concrete surface without
damage to the board or the concrete surface and with very little
physical eFfort required. In this sense, the present invention
provide extreme advantages over the present practice of using
relatively heavy plywood knee boards which tend to sink into the
concrete and scar the soft cement sur-Face and which are
cumbersome to move from one spot to another. The cleanup
required subsequent to moving one of the knee boards of the
present invention is also extremely slight compared to the damage
done by either hard support boards or soft pliable knee pads of
prior art patents discussed. The combination of rigiditY~ high
degree of buoyancy, and inherent cushioning qualities along with
moisture resistance and the moisture proofing by use of a soft
pliable skin or covering for the knee board renders the apparatus
oF the present invention usable and practical as opposed to the
complicated devlces known in the prior art. The knee board and
soFt pliable plastic cover of the present invention may be simply
washed or hosed off following use without
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damage to the board. The soft pliable skin or cover also elimi-
nates any tendency for sharp edges or corners of the board from
marring the soft moist cement surface. An upstanding strap or
handle is utilized to facilitate movement of the lightweight
pads from one position to the other as the finisher completes
the immediate area and moves backwardly.
The present invention accomplishes the advantages de-
scribed by the use of a high density rigid closed cell foam
plastic material with ~ufficient compressive strength to support
and spread the weight of the individual without cracking or
breaking or losing its dimensional stability. The material is
visco-elastic in that the surface yields steadily until a con-
stant stress level is reached. This surface yielding or defor-
mation along with partial return provides excellent protection
to the knees of the user and eliminates the need for additional
knee pads allowing the workman to stay on the surface longer.
Because of the excellent flotation quality of the buoyant foam
plastic material it is possible to get on the wet surface sooner
than with conventional heavy hard boards which need a firmer
surface for support. All o~ these advantages are gained with an
extremely simplified structure and the utilization of extremely
inexpensive materials.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view o~ the typical use of the
knee board of the present invention by a workman during trowel-
lng of a soft cement work area,
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Fig~ 2 is a perspective view of the knee board of the
present invention;
Fig. 3 is a cross sectional detail taken along lines
3-3 of Fig. 2 illustrating the board member and the protective
pliable covering and seam;
Fig. 4 is a sectional detail illustrating the yielding
and deformation of the board surface and protective covering
during use; and
Fig. 5 illustrates an alternative means for applying a
waterproof and surface protection layer to the knee board body.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Fig. 1 illustrates the use of the present knee board
wherein the workman 10 may be in a full kneeling position, i.e.
with both knees and both toes on the board. One or two trowels
11 are used to finish and smooth the fresh cement surface 12.
The cement surface is generally soft and moist during the time
of finishing. As illustrated, two knee boards 13 of the present
invention are utilized in such a manner that when the workman 10
finishes the immediate area in front and about the board 13 in
use~ he moves rearwardly onto the second knee board 13 and moves
the first knee board into a rearward position so that he may
progress incrementally across the surface of a floor or slab.
Each board 13 is provided with a handle or upstanding strap 14
to facilitate lifting and moving the board.
Referring to Figs. Z and 3, the knee board comprises a
rigid high density cellular foam plastic body 16 which is pref-
erably 1 1/2 to 2 inches in thickness and having overall length
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and width dimensions of approximately 18 - 24 inches. The dl-
mensional area covered by the board 13 may, of course, be varied
but should be sufficient to permit a workman to comfortably rest
both knees and both toes on the board during its use. As afore-
mentioned, the expanded foam plastic body 16 of the board is
sufficiently rigid to support and spread the weight of a workman
without breaking or deflecting to any appreciable extent. The
high density foam plastic 16 is covered with a waterproof jacket
17 which may be seamed around the vertical edges as at 18 to
provide a watertight seal. The waterproof or water resistant
covering 17 may be made from a variety of pliable plastic ma-
terials such as vinyls and the like. The covering 17 il-
lustrated is a fabric backed vinyl sheet which may be sewn at
the seams 18. The handle or strap 14, as shown in Fig. 2/ may
be sewn into the seam or may be otherwise securely attached to
the vinyl jacket. The vinyl or other plastic material covering
serves not only to further waterproof the expanded foam but
provides the rigid board with soft corners and edges so as to
reduce or eliminate any tendency of the board to scar the sur-
face of the moist concrete. Because of the lightweight and
buoyant characteristic of the foam plastic, however, any ten-
dency to scar the surface is greatly diminished as compared to
heavy hard boards such as plywood utilized in the prior art.
The plastic jacket provides durability to the expanded foam body
and actually protects the foam from being damaged by contact
with tools such as the hand trowels being wielded by the
workman. While the present embodiment of the invention as il-
lustrated in Figs. 1-4 ut1lizes a seamed vinyl covering, it will
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be apparent that other durable plastic coverings could be uti-
lized and seaming could be done by other methods such as heat
sealing etc. Fig. 5 illustrates another alternative for cover-
ing the cellular plastic foam by means of simply coating the
board 16 with a compatible plastic by such methods as dipping or
otherwise applying the protective layer.
Fig. 4 illustrates the characteristic of the cellular
foam plastic wherein the user's knee 21 initially causes a de-
pression or indentation 22 in the top surface of the knee board.
The visco-elastic characteristics of the board surface result in
the yielding of the surface to a point where the stress on the
material becomes constant and the material is stabiliæed. While
some degree of return will be experienced with the board sur-
face, the cushioning effect of the material on the user's knee
remains throughout use of the board.
The expanded foam material 16 is comprised of an ex-
truded closed cell polystyrene foam. This material is a high
density rigid cellular foam plastic developed around 1945 and is
available and sold under the name STYROFOAM, a trademark of Dow
Chemical Company. The product is commercially available and
commonly used as heat insulation material and is described in
the Dow Chemical Company product specification publication
~t~L~~a--~o~ccL-L~LLl~L~ p~d~9~s for ~all~, Eoun~ations and
BQQ~, 07200!DOT, Buyline ~930. The material is foamed or ex-
panded by an extrusion process a~ contrasted to the typical
molded bead polystyrene foam. The extruded closed cell material
is a high density rigid material with no voids between the
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cells. This closed cell structure results in a material which
may range from 2-3 pounds per cubic foot. The voidless closed
cell structure also results in a highly moisture resistant ma-
terial, which adds to its desirability for use in conjunction
with a wet surface environment. The relatively light weight
material provides a highly buoyant board which tends to float
better than hard board such as plywood, metal or the like. The
compressive strength of the extruded closed cell polystyrene
foam is expressed in terms of the vertical compressive loading
at which the surface will yield and deform. The compressive
strength of the extruded closed cell polystyrene foam may range
typically from a low of 25 psi (pounds per square inch~ to a
high of 70 psi.
The preferred extruded high density closed cell poly-
styrene foam which provides excellent results is in a range of
1-2 inches in thickness and weighing from 2-3 pounds per cubic
foot of material. The preferable range of compressive strength
is from 25 - 45 psi.
Excellent re~ults have been obtained using a 1 1/2 inch
extruded closed cell polystyrene foam having a weight of 2 - 2.5
pounds per cubic foot and a compression strength of 40 psi.
The knee board of the present invention provides the
essential characteristics of known prior art knee boards or knee
pads by providing an improved structure which combines the ri-
gidity necessary for 10tation and weight spreading on a soft
wet surface yet cushions and protects the u~er's knees. The
foam plastic is protected form physical damage and abuse with a
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durable and soft pliable plastic cover which also provides mois-
ture proofing for easy cleanup. This combined function is an
improvement over the prior art wherein two elements, namely a
hard board and a separate cushion is necessary. In addition,
the buoyancy obtained by the light weight foam material and the
use of a soft pliable cover significantly reduces damage to the
wet concrete surface as compared with prior art hard boards.
Although the present invention has been disclosed and
described with relation to specific embodiments, it will be
apparent to those skilled in the art that modifications may be
made without departing from the spirit of the invention or from
the scope of appended claims.
