CA1291411C - Cement finishers's knee board - Google Patents
Cement finishers's knee boardInfo
- Publication number
- CA1291411C CA1291411C CA000576118A CA576118A CA1291411C CA 1291411 C CA1291411 C CA 1291411C CA 000576118 A CA000576118 A CA 000576118A CA 576118 A CA576118 A CA 576118A CA 1291411 C CA1291411 C CA 1291411C
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- CA
- Canada
- Prior art keywords
- knee
- foam
- knee board
- board
- cement
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Abstract
ABSTRACT OF THE DISCLOSURE
A rigid light weight knee board for cement finishers.
The body of the knee board comprises a high density extruded closed cell polystyrene foam. A water repellent cover made from soft pliable vinyl is provided for the board and includes an upright handle strap.
A rigid light weight knee board for cement finishers.
The body of the knee board comprises a high density extruded closed cell polystyrene foam. A water repellent cover made from soft pliable vinyl is provided for the board and includes an upright handle strap.
Description
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 ~k ..
( ~ 9~ 4 ~1 ( 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, (~ ; ( ~9~
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 ~LX914~1 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 ~ 9~4~l -~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 . _ ~Z91~
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, _, _ ~X91~
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 I ~ X 9~
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 L4~l~
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 ~2~3~43L~
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 .
, .
12 ~ 43L
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.
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 ~k ..
( ~ 9~ 4 ~1 ( 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, (~ ; ( ~9~
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 ~LX914~1 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 ~ 9~4~l -~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 . _ ~Z91~
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, _, _ ~X91~
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 I ~ X 9~
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 L4~l~
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 ~2~3~43L~
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 .
, .
12 ~ 43L
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.
Claims (10)
1. A cement finisher's knee board comprising;
a rigid high density body member comprising extruded closed cell polystyrene foam having a thickness of from 1-2 inches and a weight from 2-3 pounds per cubic foot, said body member having at least one float surface adapted to be supported from a wet cement surface and the opposite surface thereof adapted to accommodate a kneeling workman, said surfaces being visco-elastic and having a vertical compression load capacity of from 25-45 psi, and a soft pliable water repellant cover layer surrounding said foam body member.
a rigid high density body member comprising extruded closed cell polystyrene foam having a thickness of from 1-2 inches and a weight from 2-3 pounds per cubic foot, said body member having at least one float surface adapted to be supported from a wet cement surface and the opposite surface thereof adapted to accommodate a kneeling workman, said surfaces being visco-elastic and having a vertical compression load capacity of from 25-45 psi, and a soft pliable water repellant cover layer surrounding said foam body member.
2. The knee board according to claim 1 wherein said cover layer is composed of vinyl plastic and includes carrying strap means connected thereto; said strap means extending above said opposite surface.
3. The knee board according to claim 1 wherein said body member is 1 1/2 inches thick having a weight of 2-2.5 pounds per cubic foot and a vertical compression load capacity of 40 psi.
4. A cement finisher's knee board comprising;
a rigid body member comprised of high density polystyrene foam weighing 2-3 pounds per cubic foot and having a thickness of 1 1/2 to 2 inches, said body member including first and second opposed flat surfaces adapted to be supported from a wet cement surface and to accommodate a kneeling workman respectively;
said surface being visco-elastic and having a vertical compression load capacity of 25-45 psi, and a soft pliable water repellant cover surrounding said foam body.
a rigid body member comprised of high density polystyrene foam weighing 2-3 pounds per cubic foot and having a thickness of 1 1/2 to 2 inches, said body member including first and second opposed flat surfaces adapted to be supported from a wet cement surface and to accommodate a kneeling workman respectively;
said surface being visco-elastic and having a vertical compression load capacity of 25-45 psi, and a soft pliable water repellant cover surrounding said foam body.
5. The knee board according to claim 4 wherein said cover layer is composed of vinyl plastic and includes carrying strap means connected thereto; said strap extending above said second flat surface.
6. The knee board according to claim 4 wherein said body member is 1 1/2 inches thick having a weight of 2-2.5 pounds per cubic foot and a vertical compression load capacity of 40 psi.
7. A cement finisher's knee board for supporting a person in a kneeling position on a wet uncured cement surface comprising;
a rigid expanded foam body having flat top and bottom surfaces of sufficient dimensions to accommodate both knees and both toes of a person in a kneeling position, a soft pliable water repellant cover layer surrounding said foam body, and carrying strap means connected to said cover, said foam body being comprised of extruded high density closed cell plastic foam, being approximately 1-2 inches in thickness and having a weight of 2-3 pounds per cubic foot, said foam body being visco-elastic and having a vertical compression load capacity of 26-45 psi, whereby cushioning is provided for the knees of the person while the body weight of the person is distributed over the area covered by the knee board with no substantial deflection of the board body.
a rigid expanded foam body having flat top and bottom surfaces of sufficient dimensions to accommodate both knees and both toes of a person in a kneeling position, a soft pliable water repellant cover layer surrounding said foam body, and carrying strap means connected to said cover, said foam body being comprised of extruded high density closed cell plastic foam, being approximately 1-2 inches in thickness and having a weight of 2-3 pounds per cubic foot, said foam body being visco-elastic and having a vertical compression load capacity of 26-45 psi, whereby cushioning is provided for the knees of the person while the body weight of the person is distributed over the area covered by the knee board with no substantial deflection of the board body.
8. The knee board according to claim 7 wherein said cover layer is composed of vinyl plastic and said carrying strap means is connected to said vinyl plastic cover.
9. The knee board according to claim 8 wherein said closed cell plastic foam comprising polystyrene.
10. The knee board according to claim 9 wherein said closed cell foam body is 1 1/2 inches thick having a weight of 2-2.5 pounds per cubic foot with a vertical compression load capacity of 40 psi.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000576118A CA1291411C (en) | 1988-08-30 | 1988-08-30 | Cement finishers's knee board |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000576118A CA1291411C (en) | 1988-08-30 | 1988-08-30 | Cement finishers's knee board |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1291411C true CA1291411C (en) | 1991-10-29 |
Family
ID=4138650
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000576118A Expired - Fee Related CA1291411C (en) | 1988-08-30 | 1988-08-30 | Cement finishers's knee board |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1291411C (en) |
-
1988
- 1988-08-30 CA CA000576118A patent/CA1291411C/en not_active Expired - Fee Related
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| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |