The present invention relates to a blade for a trowel and particularly, but not exclusively, to a blade for a trowel for applying plaster, paint, screed, tile adhesive, floor levelling compounds, cementitious mixes and other spreadable materials.

BACKGROUND OF THE INVENTION

Applying plaster to walls and ceilings to an acceptable standard is a skill which can take several years to master. Due to the difficulty of the task, the process of plastering is usually carried out by a trained and/or time-served plasterer. Applying plaster using a conventional trowel is difficult because the angle between the surface of the trowel and the building surface (for example, a wall) must be gradually reduced and pressure applied as the trowel is drawn along the wall and plaster on the trowel is transferred to the wall. If the optimum angle between the trowel and the wall is not maintained, then the surface tension, commonly referred to as "suction", between the trowel and plaster is likely to be greater than that between the plaster and the wall, and hence there is a risk that plaster that has already been applied will be pulled away from the wall on further movement of the trowel.

When plastering a wall, typically a first layer of plaster is applied which has to dry before a further finishing coat of plaster can be applied. The time delay between applying the two coats of plaster while the first coat is drying can have cost consequences, for example, if a tradesman cannot be utilised during the delay. Applying finish plaster is also a very time consuming and physically tiring process, because once applied, the plaster has to be finished by repeated trowelling, in order to achieve an adequately smooth surface.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a blade for a trowel comprising a front face for spreading material and a rear face adapted to be attached to a handle, the front face having at least two substantially planar portions, the substantially planar portions being separated by a step.

The front face of the blade may have a plurality of substantially planar portions

separated by a plurality of progressive steps. The substantially planar portions may be formed by lamellae.

Preferably the lamellae are disposed in a stack, each step being formed by an edge of one of the lamellae.

The lamellae may be rectangular and each lamella may have a smaller width than the previous lamella in the stack. Also, at least some of the lamellae may have a smaller length than the previous lamellae in the stack.

Preferably the lamellae are aligned about a central axis, and the steps formed by the side edges of the lamellae are parallel with one another and the steps formed by the end edges of the lamellae are parallel with one another. The smallest of the lamellae may be disposed at the centre of the stack on the front face of the blade.

A flexible member may be disposed between adjacent lamellae in the stack.

Preferably each flexible member is a lamella made from an elastomeric material. The elastomeric material may be butyl rubber, natural rubber, EPDM, silicon rubber or any other suitable material.

The lamellae and flexible members may be bonded together with adhesive.

In another embodiment of the invention at least one rib may be attached to a planar portion of the front face of the blade, and a front surface of the rib may define one of the substantially planar portions.

A plurality of spaced ribs may be attached to the front face of the blade, each rib having a front surface defining a separate planar portion.

A structural member may be disposed along the rear face of the blade and may be fastened to the blade using studs, pins and/or adhesive.

The studs or pins are preferably welded to a part of the blade and may be releasably fastened to the structural member.

The structural member may extend over either the full length of the blade or over part of the length of the blade.

A handle may be attached to the structural member.

A second aspect of the invention provides a trowel comprising a handle and a blade according to the first aspect of the invention wherein the handle is fastened to the rear face of the blade.

A second handle may be fastened to the rear face of the blade, spaced from the first handle. This enables the trowel to be held in both hands, and also allows for the manufacture and use of a longer trowel.

In another aspect of the present invention there is provided a spreadable material trowel including a handle device connected to a flexible, tensile blade, wherein at least a portion of the blade has a thickness such that, in use, when the portion of the trowel is pressed against a surface of a building structure to apply the spreadable material to it, the blade portion flexes and a tensile force within the blade and the interposition of the rib cause the fluids and the finest particles of the spreadable material to be drawn towards the blade.

The blade portion may be formed of spring steel and may have a thickness between around 0.2 mm and around 0.4 mm, but preferably about 0.3 mm. However, the blade may be formed of any other appropriate material, eg plastic.

The trowel may include at least one rib on a front surface of the blade, the main direction of the rib being substantially parallel with the length of the blade. The rib may be spaced from the side edges of the blade. It is envisaged that in use, a portion of the rib may be closer to a surface of a structure to which spreadable material is being applied and may act as a guide to the user for maintaining the trowel at an effective working angle with the structure surface. The rib may be spaced from a nearest side edge of the blade by a distance approximately equal to one quarter of the width of the trowel. The rib may have a thickness of around 2 mm, which would enable the trowel to be maintained at an angle of around 5° in use. Preferably, the trowel includes two ribs, one rib being spaced apart from a first side edge of the blade, the other rib being spaced apart from the opposite side edge of the blade.

The blade may have at least one reinforcing rib located on the blade's rear. The reinforcing rib may be located substantially above a rib on the application surface of the blade. The blade may be substantially rectangular. The handle device may be located at least partially on the surface of the blade opposite the application surface.

The handle device may normally be connected substantially half way across the width of the blade. The handle device may be longer than the length of the trowel to enable a user to apply the trowel to areas beyond that which he/she can normally reach. Such a handle may have a length of about 1 m to 1.5 m.

The blade may also include a further rib of about 4mm thickness located substantially mid-way across the width of the application surface of the blade. This substantially central rib may, in use, act both as a rib and as a pivot when the user changes which side edge of the blade is to be closer to the surface to which the spreadable material is being applied. The substantially central rib may have a curved surface.

The trowel may be connected to a tube that functions as a conduit for the spreadable material. The material may be transferred (eg by means of a pump) from a source, through the tube and out through an aperture leading to the application surface of the blade of the trowel. Thus, the user may not need to move the trowel regularly to a source of plaster in a conventional manner.

According to another aspect of the present invention there is provided a trowel for spreadable material including a handle device connected to a blade and at least one rib on an application surface of the blade, the main direction of the rib being substantially parallel with the length of the blade and the rib being spaced apart from the side edges of the blade.

According to another aspect of the present invention there is provided a portable spreadable material (eg plaster) carrier. The carrier may include a container supported on a frame that is movable by means of, for example, a set of wheels. The frame may have a height of around one metre so that the user does not need to stoop down far to put plaster on the trowel. In one embodiment the container is rotatably mounted on the frame in order to assist with mixing plaster. The container may also include a handle in order to assist with the mixing motion. The container may have a substantially

cylindrical shape with one half of the container acting as a releasably fixed lid.

According to another aspect of the present invention there is provided a spreadable material trowel including a blade having an aperture in flow communication with a conduit for the spreadable material. A controllable pump may be attached to the conduit to control the flow of the material out of the aperture for application to a surface.

According to a further aspect of the present invention there is provided a kit for applying spreadable material to a surface of a building structure, the kit including a trowel (which may be substantially as described herein) and a portable spreadable material carrier substantially as described herein.

The invention is intended to provide a means to make it easier to apply plaster and other materials to a professional standard, and to reduce the time and effort required to apply the plaster or other material.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-

Figure 1 is a perspective view of a trowel including a first embodiment of a blade of the invention;

Figure 2 is a schematic front view of the blade of Figure 1 ;

Figure 3 is a schematic end view of the trowel of Figure 1 ;

Figure 4 is a schematic side view of the trowel of Figure 1 ;

Figure 5 is a schematic rear view of the trowel of Figure 1 ;

Figure 6 is an enlarged end view of the trowel of Figure 1 ;

Figure 7 is an exploded perspective view of the trowel of Figure 1 ;

Figure 8 is a schematic end view of a trowel including a second embodiment of blade of the invention;

Figure 9 is a front view of the trowel of Figure 8;

Figure 10 is a schematic illustration of the trowel of Figure 8 in use; and

Figure 11 illustrates schematically a container for plaster that can be used in conjunction with either embodiment of trowel.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring firstly to Figure 1 , a trowel is indicated generally at 10, and comprises a first embodiment of blade 12 of the invention and a handle 14. Referring also to Figures 2 to 8, the blade 12 is made up of a plurality of rectangular lamellae 16,18,20,22, typically constructed from spring grade stainless steel and having a thickness of less than 1.0mm. In testing, it has been found that four laminae are most effective for a hand held trowel of conventional size, ie 338mm by 113mm, although there may be more or less, as desired. Sizes of the laminae are indicated in mm in Figure 2 and range from 338mm by 113mm down to 290mm by 48mm. The laminae 16,18,20,22 are arranged in a stack on the front of the blade in alignment with one another about a central axis 24, indicated in Figure 7. Flexible elastomeric laminae 17,19,21 are positioned between the spring steel laminae in the stack, and provide compliance in the assembled blade 12.

The laminae, both spring steel and elastomeric are bonded together with adhesive. The adhesive must be flexible, able to withstand shear forces, and able to resist a variety of fluids, chemicals and a range of temperatures. Infra-red, heat and/or pressure cured adhesives have proved most suitable, being the most durable in testing of the trowel 10.

The compliance laminae 17, 19,21 are important because the blade 10 can be exposed to intermittent bending forces as the trowel is used. It is understood that the

compliance laminae function to prevent the adhesive breaking down, because the compliance laminae flex, thus taking the strain off the adhesive.

As well as bonding the steel and elastomeric laminae with adhesive, a structural member 26, or spine, is disposed on the rear of the largest lamina 16, as in the construction of a conventional plastering trowel. A plurality of stainless steel pins or studs 28, shown in Figure 4, may be welded to the smallest lamina 16, and may extend through apertures in the other laminae 18,20,22 and be fastened to the structural member 26. The free ends of the studs may be either bifurcated into the structural member or may be fastened with a top-hat nut assembly (not shown).

The structural member 26 adds stiffness to the blade 12 and is shown extending along approximately half of the length of the blade 12. However, the structural member can be longer or shorter, depending on the amount of flexibility required in the blade, particularly at the blade ends. Apertures of slots (not shown) may be cut in the stainless steel laminae 16,18,20,22 to reduce their stiffness as desired. The handle 14 is fastened to the structural member 26 in conventional manner. The handle 14 can be made from any suitable material, and can be covered with a flexible grip, as required.

The face of the assembled blade 12, as shown in Fig 1, includes a plurality of planar portions 32,34,36,38, formed by the laminae 16,18,20,22, which are separated by progressive steps 35,37,39 formed by the edges of the laminae. Because the rectangular laminae are aligned with one another, the steps 35,37,39 from one side of the laminae to the other are parallel, as are the steps from end to end.

The operation of the trowel 10 will now be described with reference in particular to Figure 6. The trowel 10 is shown with its working surface, ie its front surface, at an angle to a substrate 30. The outward corners of the edges of the parallel steps 35,37,39 are closest to the substrate, and in contact with the spreadable material, for example, plaster 40, which is spread on the substrate by the planar portions 32,34,36,38 of the laminae. The trowel is being moved in a direction, indicated by the arrow A, parallel with the substrate.

The plaster 40 forms a series of hydrodynamic wedges. It is currently thought that the flow within each wedge enables the spreadable material to be compressed and then released as it passes the edge of the step, producing both separation and grading of

particulate media and the fluid(s) in which it is contained. This action speeds and facilitates the densification and distribution of bulk viscous media in the plaster mixture.

The shape of the trowel's working surface enables small quantities of media to be captured where excess is present, and released where insufficient material is available, to form a flat surface. This process is realised through the formation of equilibrium and non-stable hydrodynamic conditions formed as the trowel's working surface is swept over the area upon which the viscous media is being spread.

The trowel's stepped working surface minimises adhesion of viscous media to the trowel when relative surface speeds are low, facilitating loading of product onto the area upon which the viscous media is being distributed. As relative surface speeds are increased, a filtering effect becomes apparent at the surface of the media being spread. This is a result of the grading of particles and fluids within the viscous media. In certain applications this effect is beneficial in rapidly producing a surface with a high degree of smoothness. Under certain controllable conditions of angle of approach or flexural loading of the trowel, a full hydrodynamic glide condition may be established assisting in the rapid formation of a polished surface.

The operation of the trowel, as described above, means that the force applied to the trowel is normally significantly less than that required for a conventional trowel. In other words, the physical exertion to apply, for example, plaster, is much less than that for a conventional trowel. The multiple points of application, ie contact at each edge of a lamina, provides a much smoother surface in one pass, than with a conventional trowel with a single contact edge. It has been found that in some cases the amount of coats of plaster can be reduced as a result of this effect.

Referring now to Figures 8 and 9, a trowel indicated generally at 100 includes a second embodiment of a rectangular blade 102. In the example, the blade has a length (illustrated by arrows 100L) of around 390 mm and a width (illustrated by arrows 100W) of around 127 mm. In general, the length of the blade could be between 250 mm (or less) and 900 mm. The blade is formed of a flat plate of spring steel (typically a type of rolled steel having a high carbon or alloy content) having a uniform thickness (illustrated by arrows 102Y) of around 0.3 mm, although the thickness of the steel may be in the range of around 0.2 mm to around 0.4 mm. However, it will be appreciated that a blade formed of another suitable material (or combination of materials) and/or

having different dimensions could be used to provide a blade with suitably flexible/tensile properties. For example, the blade can have a non-uniform thickness, being thicker at a central portion and becoming thinner towards at least one of its side edges.

Further, although the blade 102 shown in the example is formed of a single sheet of material, it will be appreciated that the blade could comprise two or more separate pieces attached together in a suitable manner (eg welded).

A handle 103 is connected to the middle of the upper surface of the blade 102. In the embodiment shown, the handle has a conventional generally cylindrical design suitable for being gripped directly by the user. The length of the handle 103 in the example is no greater than the length of the blade 102 and the main length of the handle is generally parallel with the length of the blade.

Attached to (or formed on) the surface of the blade 102 that is used to apply plaster to a surface of a structure (the lower surface of the blade in the example shown in the Figures) are two elongate ribs 104A, 104B. Each rib has a width (illustrated by arrows 104X) of around 10 mm and a thickness (illustrated by arrows 104Y) of about 2mm. The main direction of each rib is generally parallel with the length of the blade. The length of each rib in the example is substantially the same as the length of the blade 102 and so each rib runs substantially all the way from one end 102A of the blade to the opposite end 102B. However, there could be gap of up to around 28 mm between at least one end of at least one rib and the adjacent end(s) of the blade.

The distance (illustrated by arrows 102X) between the left hand side edge 102C of the blade and the adjacent side surface of the first rib 104A is around 28 mm. The distance between the right hand side edge 100D of the blade and the adjacent side surface of the second rib 104B is also about 28 mm. Thus, each rib is spaced from the nearest side edge of the blade by a distance that is approximately equal to one quarter of the width of the blade.

Also located on the lower surface of the blade 102 is a substantially central rib 105. The central rib 105 will typically have the same length as the ribs 104A, 104B and is substantially parallel with them. The central rib has a with (illustrated by arrows 105X) of around 15 mm and a thickness (illustrated by arrows 105Y) of around 4 mm.

The gap between the side surface of the first (left-hand in the Figures) rib 104A and the adjacent side surface of the central rib 105 (illustrated by arrows 102XX) is around 18 mm. Similarly, the distance between the side surface of the right hand rib 104B and the adjacent side surface of the central rib 105 is 18 mm.

As can be seen in Figure 8, two reinforcing ribs 106A, 106B are located on the upper surface of the blade 102, directly above the two lower surface ribs 104A, 104B. The upper ribs 106A, 106B will normally have approximately the same length and width as the corresponding lower ribs 104A, 104B, although the thickness of the upper ribs may be around twice that of the lower ribs, eg about 4 mm.

It will be appreciated that the various ribs may be formed of steel or any other suitably rigid material and can be attached to the blade by various means, eg bolts, rivets, strong adhesives or welding. Alternatively, at least some of the ribs may be integrally formed with the trowel blade during manufacture. Further, although the ribs in the Figures are shown are being constructed of a single continuous elongate strip, one or more of them could be formed of more than one piece arranged to forrri a continuous rib. The surfaces of the ribs 104A, 104B and 105 are planar and are stepped away from the planar surface of the base lamina of the blade 102.

Turning to Figure 10, there is illustrated schematically an example of how the trowel 100 can be used to apply plaster to a surface of a building structure. A typical example of such a surface is building wall 300, but the trowel can also be used to apply plaster to other building surfaces such as ceilings. The user first places an amount of plaster on the lower surface of the blade 102 and then moves that surface to face the wall 300. A portion (labelled using arrows 302) of the blade's (about 10 mm of its width) side edge is then pressed against the wall. In the example of Figure 10, part of the blade is to be drawn along the wall in a curved, but generally upwards direction (illustrated by arrow 304) for the application of plaster to an area of the wall. In this case, the side edge 102C of the blade is closest to the wall. The corner of the edge of the first lower surface rib 104A will normally contact the wall at this stage and this can act as a guide for the user so that he/she holds the main, un-flexed portion of the lower surface of the trowel blade at an effective working angle (eg around 5°) with the wall substantially throughout the plaster application motion. Because the trowel can be held by the user at a substantially constant angle throughout a plaster application motion, he/she does

not need to reduce the angle as plaster is transferred to the wall as with conventional trowels. The position of the rib with respect to the side edge of the blade can also influence the width of the portion 302 of the blade that contacts the wall.

The pressure exerted on the trowel by the user causes the blade portion 302 to flex (whilst the remainder of the blade remains substantially flat). The pressure also spreads and flattens some of the plaster on and around that portion of the blade onto the wall, whilst another amount of the plaster is pushed further inboard along the blade towards the first rib 104A. A space 306 (generally triangular in shape as viewed in Figure 10) between the wall 300, the side surface of the rib 104A and part of the lower surface of the blade (between where the portion 302 contacts the wall and the side edge of rib 104A) acts as a "reservoir" for plaster that is gathered there in this way. If there are gaps between the ends 102A, 102B of the blade and the ends of the ribs then this can allow the plaster to flow around the ribs into the reservoir. Such gaps can also allow the end(s) of the blade to "kick up", which can reduce or eliminate lines in the applied plaster.

There will normally be a gap of around 2 mm between the wall and the adjacent corner of the edge of the central rib 105. Plaster will fill the space defined between the adjacent side surface of the rib 104A and the central rib 105.

It is believed that due to the flexible, tensile properties of the blade, as the blade moves over the substrate the viscous media remains in the blade portion 302 and forms a hydrodynamic wedge. Plaster is a mixture of water and grains/particles (typically sand and lime) of varying sizes. The smaller particles may be drawn up towards the surface rather than the larger ones, which gives a more "finished" appearance to the area of the wall that has had plaster applied to it by the trowel 100. As the trowel is drawn further along the wall, the contacting blade portion 302 then smoothes the applied layer of plaster.

After the user has completed a plaster application motion in the general direction of arrow 304, he/she then reverses the direction of the movement of the trowel 100 (in a generally opposite second direction shown by arrow 304A) to further smooth the plaster that has just been applied. This will typically involve lowering the other side of the trowel blade 102 onto the wall 300 so that a portion (again around 10 mm of the width of the blade) of the blade leading from the other side edge 102D is pressed

towards the wall. The central lower surface rib 105 may be used by the user to pivot the trowel in a "see-saw" motion during this change in direction. In fact, the central rib 105 may have a curved surface to assist with this movement. The proximity of the comer of the edge of the second lower surface rib 104B and the wall 300 can help the user to hold the trowel at an effective working angle whilst moving the trowel in the second direction.

Although the blade 102 shown in the example is flat, in some cases a curved blade (eg concave with respect to the structure surface) may produce beneficial results. Further, although the trowel 100 is mainly intended for use in applying plaster, the inventor has also found that it is also effective in applying other spreadable materials, including paint, to surfaces.

In an alternative embodiment, a long (eg around 1 to 1.5 m) handle/pole may be connected to the trowel that enables the user to apply the trowel to areas beyond his/her normal reach. The relative ease-of-use of the trowel 100 compared with conventional ones means that it can be used effectively with such an extended handle.

In an alternative embodiment, instead of having a pair of lower surface ribs 104A, 104B, there is a single lower surface rib, which can be located substantially half way along the width of the lower surface of the blade 102. This single rib can work in a similar manner to the two-ribbed version described above, but the inventor has found that having a rib located nearer to a side edge of the blade can be more effective in helping the user hold the trowel at a desired working angle, for example. Also, having two lower surface ribs means that the trowel is more efficient when changing the direction of a plaster application motion as discussed above. In another alternative embodiment, the trowel may comprise two or more flexible blades attached to a main body in an arrangement similar to some existing shaving razor blades.

Referring to Figure 11 , an example of a portable spreadable material (eg plaster) carrier 400 is illustrated. Conventionally, plaster is carried on a handheld square board called a hawk. This is only capable of holding a relatively small amount of plaster and so has to be replenished fairly often. Also, the user holds the hawk in one hand whilst he/she is using the other hand to plaster and this arrangement can be inconvenient to use. The carrier 400 includes a supporting frame 402 that holds a container 404 at a height of between around 0.5 and 1 metres above the base of the frame. Thus, the

user does not have to stoop far to put plaster on the trowel. The height of the frame 402 may be adjustable. To make the portable carrier 400 easily movable, it may be provided with a set of wheels 406 fitted to the base of the frame 402.

In the example, the container 404 has a substantially cylindrical shape, with one half of the cylinder being pivotally connected to the other half, which enables one of the halves to act as a lid. It will be appreciated that other shapes/designs can be used for the container 404. The cylindrical container 404 may be rotatably mounted on the frame 402 by means of a spindle, which allows the container to be spun (when closed) to assist with mixing the material it holds. A handle 408 may be attached to the portable container 400 to aid rotation. The portable container 400 can be drawn along the floor conveniently as the user moves whilst plastering.

Also shown in Figure 11 is a tube 412, one end of which is located in a supply of plaster (in this case the container 404). the tube 412 can be attached to a pump that transfers plaster from the supply to the other end of the tube, which can be attached to a modified trowel 414. Such a modified trowel includes an aperture 416 on its lower surface to enable plaster that has been pumped through the tube 412 to be applied to the wall. Such an arrangement can be particularly advantageous when a longer handle/pole is used in connection with the trowel.

Although illustrative embodiments of the invention have been shown and described, the features of the different embodiments are considered to be interchangeable by the skilled man within the scope of the claims. Furthermore, the carrier 400 can be utilised with trowels including either embodiment of blade described.