AU2021201567A1

AU2021201567A1 - Improved Jointing System

Info

Publication number: AU2021201567A1
Application number: AU2021201567A
Authority: AU
Inventors: Edward Gale; Adnan Javed
Original assignee: CSR Building Products Ltd
Current assignee: CSR Building Products Ltd
Priority date: 2014-11-11
Filing date: 2021-03-11
Publication date: 2021-04-01
Anticipated expiration: 2035-11-11
Also published as: AU2015255227A1; NZ714102A; AU2020294227A1; AU2021201567B2

Abstract

A method and system for the rapid formation of a joint at adjacent sheets/panels of plasterboard and cellulose-cement board (e.g. for walls and ceilings) is disclosed. The method and system provides for a two-coat methodology and system, whereby a second coat application of base coat can be eliminated, with the attendant advantages of speed, reduced cost and reduced complexity. The base coat is able to provide underlying joint strength whilst having low shrinkage and good adhesion to the tape. The topping compound also has a comparable degree of low shrinkage, as well as good spread-ability, high sand-ability and a smooth surface finish once applied and sanded.

Description

IMPROVED JOINTING SYSTEM TECHNICAL FIELD

Disclosed is an improved jointing method and system for the formation of a joint between adjacent, in situ panels of building material. The method and system find particular, though not exclusive, application to the jointing of plasterboard and cellulose-cement boards, and will primarily be described in this context.

BACKGROUND

Plasterboard and cellulose-cement panels, formed with recessed edges, are used in construction to provide an internal lining for walls and ceilings. To provide a smooth, paintable joint between adjacent panels, the panels are joined using a base coat jointing compound, jointing tape to reinforce the joint and a topping compound to provide a smooth, easy-to-sand finish. The base coat is applied in two stages. The first stage involves applying a first coat of the base coat to secure the tape therein. This can involve applying a small amount of the base coat to the joint, applying the jointing tape along and over the joint, and applying additional base coat to cover the jointing tape. The first coat of base coat is allowed to set before the second stage commences. In the second stage, a second coat of the base coat is applied to cover the first coat of base coat, with the embedded tape, and level the surface. The topping compound may be formulated to have a similar colour to the externally facing paper of the plasterboard, and is applied to provide a smooth finish and to better hide the joint once painted (a so-called "Level 4 finish"). To provide a surface finish that is sufficiently high in quality to meet the highest building standard (a so-called "Level 5 finish"), a final skim or "finish" coat is thereafter applied over the whole wall.

Because the base coat is used together with the jointing tape, and because it also provides the underlying joint strength between the adjacent panels, the base coat is formulated to have good adhesion to both board and jointing tape, adequate strength and low shrinkage. In this regard, it can be formulated using calcium sulphate hemihydrate plaster to set and harden relatively quickly via a reaction with water (a so-called "setting" compound). On the other hand, the topping compound requires good spread-ability (i.e. easily trowelled), high sand-ability (i.e. easily sanded), and a good (e.g. smooth) surface finish once applied and sanded. In this regard, it can be formulated from a water-based polymeric binder (a so-called "drying" compound). Thus, the base and topping compounds are formulated differently.

Whilst the setting compound employed for the two coats of base coat can be formulated to set quickly (e.g. 20 - 60 minutes) to be ready for application of the topping compound, the topping compound needs to dry for a sufficient period (16 24 hours) before it can be sanded and painted. In practice, this means that the jointing procedure for a Level 4 finish takes longer than one day. For a Level 5 finish, further time must be provided for application of the skim coat, drying and sanding. Hence, up to three days can be required before a Level 5 finished surface is ready for painting.

US8257526 to the present applicant discloses a system of jointing and finishing plasterboard sheets in which a connective material is first applied to securely join a side edge portion of a first plasterboard sheet to a side edge portion of a second plasterboard sheet. A joint filling compound is applied to overlie the connective material, and a finishing compound is then applied to overlie the joint filling compound. US8257526 teaches the addition of a chemical agent, such as potassium or ammonium sulfate, in the region of the first and second plasterboard sheets to catalyse the curing/setting reaction of the joint filling compound.

The above references to the background art do not constitute an admission that the art forms part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the jointing method and system as disclosed herein.

SUMMARY OF DISCLOSURE

Disclosed herein is a two-coat method for the jointing of adjacent, in situ plasterboard building panels (e.g. building panels of plasterboard or cellulose-cement board for walls and ceilings, etc).

The two-coat method comprises applying a base coat at ajoint of the adjacent panels and allowing it to set. The method also comprises applying a topping compound over the base coat and allowing it to set. Each of the base coat and the topping compound comprise calcium sulphate hemihydrate and a lightweight filler material.

In accordance with the present disclosure, the two-coat method and system according to the present disclosure enables a second coat application of basecoat to be eliminated, with the attendant advantages of speed, reduced cost and reduced complexity. In this regard, a first coat application of the base coat can be applied at a joint of the adjacent panels and allowed to set (optionally with reinforcing tape embedded therein), and then the topping compound can be applied over the first coat application of the base coat and allowed to set.

In accordance with the present disclosure, the base coat can be formulated to have a low degree of shrinkage.

By formulating each of the base coat and the topping compound to comprise calcium sulphate hemihydrate, the base coat and topping compound can be made to set relatively quickly and with low shrinkage (as compared to so called 'drying-type' formulations). In this regard, a higher proportion of plaster will typically result in lower shrinkage during setting.

The inclusion of a lightweight filler material in each of the base coat and topping formulations may also serve to reduce shrinkage during setting. A lightweight filler material can also impart light-weight (i.e. reduce the density of) each of the base coat and topping compound, without compromising joint strength. Such a material can further provide for ease of handling and, particularly, ease of sanding. For example, the lightweight filler material may comprise perlite microspheres, or may comprise other lightweight fillers such as cenospheres, hollow glass microspheres, expanded silicates or polymeric microspheres, etc.

The proportion of lightweight filler material in the base coat can, according to its function in the joint, be less than in the topping compound. For example, the base coat can comprise more of the setting component (e.g. more beta-calcium sulphate hemihydrate) than the topping compound. In this way, the base coat can provide for joint strength, whereas the greater amount of filler in the topping compound can provide improved ease of handling, ease of spreadability, and ease of sanding, contributing to an improved surface finish (i.e. allowing for at least a Level 4 surface finish).

In some embodiments, the topping compound can be formulated to have a degree of shrinkage comparable to the base coat. This allows for the possibility of a two-coat methodology to be deployed. In this regard, the comparable degree of shrinkage between the base coat and topping compound means that the requirement for a second coat of base coat can be eliminated whilst still achieving at least a Level 4 finish. This two-coat methodology can thus provide savings in time, cost and complexity.

In a first form, and in contradistinction to the teaching in the art, each of the base coat and topping compound are formulated to be of a setting type. The formulation of each as a setting type compound can allow for the comparable degree of shrinkage to be provided. However, the formulation of each as a setting type can also allow for the possibility of the method to be deployed quickly (e.g. in a single working day, whereby the topping coat may be sufficiently hard and dry to be surface finished (e.g. sanded) at the end of one day, to be ready for painting the next). The ability to fix board and complete jointing in one working day, and paint it the next represents a significant advance in the art, and substantially increases building productivity.

In this first form, each of the base coat and topping compound comprise a plaster-based setting compound, and each can be formulated to provide the comparable degree of shrinkage. In this regard, the plaster may comprise a beta calcium sulphate hemihydrate, the beta-form being of relatively low cost to produce compared to alpha-gypsum hemihydrate. However, alpha-calcium sulphate hemihydrate can also be used.

In this first form, the proportion of plaster in the base coat can be greater than that in the topping compound. This can result in the base coat providing adequate underlying wet strength to the resultant joint during setting. The relatively lower proportion of plaster in the topping compound can also contribute to improved sandability of the topping compound, providing for at least a Level 4 surface finish to be achieved in sanding. In this regard, the combined effects of a lower proportion of plaster and a higher proportion of lightweight filler in the topping compound (as compared to the base coat) can achieve the dual purpose of maintaining sufficiently comparable shrinkage to the base coat (to prevent cracking during setting/drying for example), whilst providing for improved sandability, such that a joint having a Level 4 surface finish can be achieved within a single working day, using the two-coat method.

In this first form, each of the base coat and topping compound can be formulated to have a short setting time. For example, the base coat can be formulated to have an initial setting time of approximately 45 - 60 min, or less than 45 min. And for example, the topping compound can be formulated to have an initial setting time of approximately 45 - 60 min, or less than 45 min.

In this first form, each of the base coat and topping compound can comprise a water soluble or dispersible polymeric binder. Such a binder can improve the strength and adhesion of the set compound. For example, the water soluble or dispersible polymeric binder may comprise one or more of: polyvinyl alcohol, starch, a polymer emulsion of: ethylene vinyl acetate; polyvinyl acetate; acrylic; polyacrylamide; styrene acrylic; styrene butadiene rubber.

In this first form, the proportion of polymeric binder in the base coat can be greater than that in the topping compound. This can result in the base coat having good dry strength and adhesion, thus providing underlying strength to the resultant joint, whereas the topping compound can also have a short setting time and sufficient adhesion but yet still be easy to: handle, spread/apply and sand/finish.

In a second form, the topping compound can be formulated to be of a drying type. The topping compound can, in this regard, comprise one or more organic binders (e.g. one or more water soluble or dispersible polymeric binders). However, in contradistinction to the prior art, the topping compound can be reformulated to have a degree of shrinkage that is comparable to the base coat.

In this second form, each of the base coat and topping compound can comprise a water soluble or dispersible polymeric binder. Such a binder can improve the strength and adhesion of each of the base coat and topping compound. For example, the water soluble or dispersible polymeric binder may comprise one or more of: polyvinyl alcohol, starch, a polymer emulsion of: ethylene vinyl acetate; polyvinyl acetate; acrylic; polyacrylamide; styrene acrylic; styrene butadiene rubber.

In this second form, the drying type formulation of the topping compound can comprise a comparatively higher level of filler than the setting type topping compound formulation. This higher level of filler can again help in providing the topping compound with a comparable degree of shrinkage to the base coat.

In this second form, the drying type formulation can comprise a dispersant that is selected to disperse the comparatively higher level of filler in an aqueous phase of the topping compound. For example, the dispersant can comprise one or more of: a hydrophobic copolymer carboxylate polyelectrolyte; an ionic dispersant such as ammonium/sodium polyacrylate, or polyacylic acid; a non-ionic dispersant such as a modified polyacrylate polymer, a modified polyurethane polymer, or an ethoxylate acetylene diols. The level of dispersant can be selected to promote a low shrinkage drying of the topping compound comparable to the base coat.

In one embodiment of either the first or second form, the topping compound can be formulated to enable its ease of surface finishing (e.g. sanding). When the base coat and topping compound are each of a setting type, their formulations can be varied according to their function in the joint.

In one embodiment of the second form, each of the base coat and topping compound can comprise filler material. The proportion of filler material in the base coat can, according to its function in the joint, be less than in the topping compound. For example, the base coat can comprise more of the mineral binder (e.g. more beta calcium sulphate hemihydrate) than the topping compound.

In either the first or second form, the base coat provides for joint strength, whereas the greater amount of filler in the topping compound can provide for ease of handling, ease of spreadability, and ease of sanding.

In one embodiment of either the first or second form, thefiller material may comprise a metal carbonate-based material such as calcium carbonate. The filler material may further comprise a filler that improves slip and sand-ability such as talc or mica. For example, the base coat may comprise mica for good mix-ability and crack resistance, whereas the topping compound may comprise talc and/or clay for good rheology and sand-ability.

In one embodiment of the second form, a proportion of the filler material in each of the base coat and topping compound can comprise lightweight filler material. Such a material can help to reduce shrinkage and can also impart light-weight (i.e. reduce the density of) each of the base coat and topping compound, without compromising joint strength. Such a material can further provide for ease of handling and ease of sanding. For example, the lightweight filler material may comprise perlite microspheres, or may comprise other lightweight fillers such as cenospheres, hollow glass microspheres, expanded silicates or polymeric microspheres, etc.

In one embodiment of either the first or second form, the proportion of lightweight filler material in the base coat can be less than that in the topping compound. This is because the lightweight filler material (e.g. perlite microspheres) can promote low-shrinkage and improve the surface finish, sand-ability and paint ability of both the setting and drying type topping compounds.

In one embodiment of either the first or second form, the base coat can be applied together with a reinforcing tape that is placed to cover a central part of the joint, prior to setting of the base coat. More specifically, the base coat can first be applied at the joint between adjacent building material sheets/panels and, after a short period (up to one minute), the reinforcing tape can be bedded into the base coat. Then, a further thin layer of base coat can be applied over the reinforcing tape, and this can all take place within the one setting procedure. Alternatively, the reinforcing tape may be applied (e.g. adhered) directly to the joint and the base coat may be applied thereover. Once the base coat applied during either of these procedures has set sufficiently, then the topping compound is applied, allowed to set or dry, and is then surface finished (e.g. sanded). With the first form of the present method and system, this can all take place in one working day.

In one embodiment of either the first or second form, the reinforcing tape can be formed from a material that is resistant to swelling (i.e. due to water absorption when wet), and that is resistant to shrinkage during setting and drying of the joint

(i.e. after contact with water and subsequent setting/drying). For example, the reinforcing tape may comprise a glass fibre mat material of elongate format. Further, where an open fibre pattern is provided in the tape, this can allow for penetration of the base coat through the fibres, which can further improve the strength of the joint. Such a tape may have thicker fibres, to assist with adhesion between the base coat and the fibres in the reinforcing tape, to improve the strength of the resultantjoint. A glass fibre tape can also help to reduce blisters/bubbles in the joint (which is a known problem with paper tape). Such a tape can therefore enable a smooth finish for the first coat, (i.e. in comparison to a paper-based tape which can deform and shrink).

Also disclosed herein is a system for the jointing of adjacent, in situ building panels (e.g. building panels of plasterboard for walls and ceilings, etc).

The system employs a base coat which is formulated as a setting type compound to be applied at a joint of the adjacent panels and allowed to set.

The system further employs a topping compound which is formulated to have a degree of shrinkage comparable to the base coat, the topping compound to be applied over the base coat and allowed to set or dry.

As mentioned above, by formulating the topping compound to have a degree of shrinkage comparable to the base coat, a two-coat system can result, with the attendant savings in time, cost and complexity.

As set forth above, when the topping compound is of a setting type, the two coat system can be deployed quickly (e.g. in one single working day), representing a significant advance in the art.

The system can also employ a reinforcing tape that is embedded into the base coat to be arranged along and to cover a central part of the joint. In an alternative form, the reinforcing tape may be applied (e.g. adhered) directly to the joint and the base coat may be applied thereover. The reinforcing tape may be formed from a material that is resistant to swelling (i.e. due to water absorption when wet) and shrinkage during drying of the base coat, such as glass fibre mat. The reinforcing tape may have an elongate format (e.g. to be cut to the joint length and of e.g. 50 mm width). The reinforcing tape may also have an open fibre pattern.

In one embodiment of the system, the base coat can be formulated such that, after application at the joint, it has an initial setting time of approximately 45 - 60 min or less than 45 min, and is sufficiently set (i.e. for application of the topping compound) after approximately 75 min-90 min.

When the topping compound is of a setting type, it can be formulated such that, after application over the set base coat incorporating the reinforcing tape, it can have an initial setting time of approximately 45 - 60 min or less than 45 mins. For example, and as set forth above, the topping compound may be applied to the base coat, incorporating the reinforcing tape, approximately 75-90 min after the base coat has first been applied. This can, for example, take place in the morning of a working day. Once the topping compound has set and sufficiently dried, it can, for example, be surface finished (e.g. sanded) on the same working day (e.g. afternoon).

When the topping compound is of a drying type, it can be formulated such that, after application over the set base coat incorporating the reinforcing tape, it can have a drying time of approximately 16 - 24 hours (i.e. overnight).

The base coat and topping compound can otherwise be formulated in a manner as set forth in the method disclosed above.

Also disclosed herein is a system for the jointing of adjacent, in situ building panels (e.g. building panels of plasterboard for walls and ceilings, etc). The system employs a base coat which is formulated as a setting type compound to be applied at a joint of the adjacent panels and allowed to set. The system further employs a topping compound which is also formulated to be of a setting type.

BRIEF DESCRIPTION OF DRAWINGS

Notwithstanding any other forms that may fall within the scope of the method and system as set forth in the Summary, a specific embodiment will now be described, by way of example only, with reference to the accompanying drawing in which:

Figure 1 shows a schematic overview of the formation of a joint between adjacent, in situ panels.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

In the following detailed description, the illustrative embodiments described are not intended to be limiting. Other embodiments may be utilised and other changes may be made without departing from the spirit or scope of the subject matter disclosed herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, can be arranged, substituted, combined, separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure.

A method and system according to the present disclosure finds particular application to the rapid formation of an excellent joint at adjacent sheets/panels of plasterboard and cellulose-cement board (e.g. for walls and ceilings). The method and system according to the present disclosure provides for a two-coat methodology and system, whereby a second coat application of basecoat can be eliminated, with the attendant advantages of speed, reduced cost and reduced complexity.

In this regard, the base coat is able to provide underlying joint strength whilst having low shrinkage and good adhesion to the tape. The topping compound also has a comparable degree of low shrinkage, as well as good spread-ability, high sand ability and a smooth surface finish once applied and sanded.

In a first mode, when the topping compound is of a setting type, it enables the two-coat methodology and system to be deployed in a normal working day. In a second mode, the topping compound is of a drying type, but is formulated to have low shrinkage, comparable to the base coat.

First Mode

Each of the base coat and topping compound is formulated to be of a setting type, whereby they have comparable degrees of shrinkage. In addition, the method and system can be rapidly deployed (e.g. in a single working day). In this regard, the base coat and topping compound are each able to set and harden sufficiently such that, at the end of the working day, the joint is able to be surfacefinished (e.g. sanded), whereby the joint is ready for painting the next day. The ability to fix boards and complete the jointing in one working day, and paint it the next, represents a significant advance in the art, which can substantially increase productivity in the building industry.

For use with plasterboard and cellulose-cement board, optimally the base coat and topping compound each comprise a plaster-based, setting compound. A preferred setting compound is beta-calcium sulphate hemihydrate, because it has relatively low cost of production (i.e. compared to alpha-gypsum hemihydrate). The proportion of plaster in the base coat compound is greater than in the topping coat compound because the base coat provides the underlying strength to the resultant joint, whereas the topping compound is formulated to enable its ease of application and surface finishing (e.g. sanding).

To enhance strength and adhesion, each of the base coat and topping compound further comprise a water soluble or dispersible polymeric binder, optimally including ethylene vinyl acetate and polyvinyl alcohol (although other suitable binders include starch, polyvinyl acetate; acrylic; polyacrylamide; styrene acrylic; styrene butadiene rubber, etc.).

The proportion of both plaster setting agent and polymeric binder in the base coat is greater than in the topping compound because the base coat provides the underlying strength in the resultantjoint. However, whilst the topping compound still has relatively short working life, its lesser amounts of binders make it easier to handle, spread/apply and sand/finish.

In this regard, each of the base coat and topping compound is formulated to have a short initial setting time (approximately 45 - 60 min. for the base coat and approximately 45 - 60 min. for the topping compound).

Second Mode

The base coat is formulated to be of a setting type, whereas the topping compound is formulated to be of a drying type. The topping compound is formulated to have a degree of shrinkage comparable to the base coat. The method and system, being two-coat, is still able to be rapidly deployed (e.g. only two coats required, and both coats applied in one working day).

In this regard, because the topping compound can be applied to the base coat after approximately 75 minutes, it can dry sufficiently (e.g. in 16 - 24 hours) such that, at or close to the beginning of the next working day, the joint is able to be surface finished (e.g. sanded). Thus, again, the joint can then be ready for painting on that day. Again, this ability to fix board and complete jointing with two coats in one working day, and paint it the next, represents a significant advance in the art, which can substantially increase productivity in the building industry.

In the second mode, the base coat is formulated as in the first mode, to provide the underlying strength to the resultantjoint. Again, the drying-type topping compound is formulated to enable its ease of application and surface finishing (e.g. sanding).

To enhance strength and adhesion, each of the base coat and topping compound comprise an organic binder such as a water soluble or dispersible polymeric binder. Optimally the polymeric binder includes ethylene vinyl acetate and polyvinyl alcohol (although other suitable binders include starch, polyvinyl acetate; acrylic; polyacrylamide; styrene acrylic; styrene butadiene rubber, etc). Polyvinyl alcohol has the added benefit of providing a thickening function. However, the proportion of polymeric binder in the topping compound can be greater than in the base coat as it forms the primary binder of the drying-type topping compound.

First & Second Modes - Further Components

Each of the base coat and topping compound in both the first and second modes comprise filler material, typically a mineral filler such as a metal carbonate based material (e.g. calcium carbonate). The proportion of filler material in the base coat is less than in the topping compound because the base coat comprises more binder than the topping compound. The greater amount of filler in the topping compound enhances ease of handling, ease of spreadability, and ease of sanding.

The filler material also includes a filler that improves rheology and sand ability such as talc or mica. More specifically, the base coat comprises mica, whereas the topping compound comprises talc. Mica in the base coat provides good mix-ability and crack resistance. Talc in the topping compound provides good rheology to the compound during its application and good sand-ability after setting and drying.

The filler material in each of the base coat and topping compound also comprises lightweight filler material to reduce the density of each of the base coat and topping compound without excessively compromising strength. The lightweight filler material can also increase ease of handling. For example, the lightweight filler material can be perlite microspheres or can be other lightweight fillers such as cenospheres, hollow glass microspheres, expanded silicates or polymeric microspheres, etc. Such lightweight fillers can also help to reduce shrinkage of each of the base coat and topping compound prior to setting.

The proportion of lightweight filler (e.g. perlite microspheres) in the base coat is less than in the topping compound because such lightweight filler additionally improves surface finish, sand-ability and paint-ability.

The combined effect of a lower proportion of calcium sulphate hemihydrate and a higher proportion of lightweight filler in the topping compound (as compared to the base coat) can achieve the dual purpose of maintaining sufficiently comparable shrinkage to the base coat (to prevent cracking during setting/drying for example), whilst providing for improved sandability, such that a joint having a Level 4 surface finish can be achieved within a single working day, using the two-coat method.

The method and system employ a reinforcing tape that is arranged along and is embedded in the base coat prior to its setting, thereby covering a central part of the joint. Alternatively, the reinforcing tape, such as an adhesive reinforcing tape, may be applied (e.g. adhered) directly to the joint and the base coat compound may be applied over the reinforcing tape. Optimally the reinforcing tape is formed from a material that is resistant to swelling, shrinkage and deformation (e.g. glass fibre mat material in an elongate format). Such swelling can occur due to water absorption by some types of tape (e.g. paper). Further, such shrinkage can occur during drying of some types of tape (e.g. paper). A glass fibre tape can also help to reduce blisters/bubbles in the joint (a known problem with paper tape). Such a tape can therefore enable a smooth surface finish for the base coat, because the tape doesn't swell, shrink or deform (i.e. in comparison to a paper-based tape).

A glass fibre reinforcing tape can also be selected that has an open fibre pattern. This can allow the base coat to penetrate through and between the fibres, and to fuse across the tape, which can further improve the strength of the joint.

Example 1 - Deployment of the Method & System

Figure 1 schematically depicts a two-coat method and system 10 for the jointing of adjacent, in situ building panels P of plasterboard (or cellulose-cement boards) for walls and ceilings.

Figure 1A shows a setting type base coat 12 first being applied in a recess R of a joint J located at adjacent panels P. This first application of the base coat is applied to fill the recess and immediately thereafter a reinforcing tape 14 (e.g. a roll of 50mm wide shrink-resistant glass fibre mat) is then applied along and over (i.e. to cover) a central part of the joint J using a suitably bladed tool (e.g. broad-knife or trowel) B.

Figure 1B shows a further layer of the base coat 12 being applied over the tape 14 again using a suitably bladed tool (e.g. broad-knife or trowel) B, and to a width of e.g. -150 - 200mm, with this operation taking place usually after a few minutes, and within the one setting procedure of the base coat (which procedure usually takes place over a 45 - 60 minute interval).

Referring now to Figure IC, once the base coat has set sufficiently (e.g. -75 90 minutes after first being applied), a setting or drying type topping compound 16 is applied with a trowel T and is allowed to set or dry. The setting-type topping compound can initially set in about a 45 - 60 minute interval, or in some cases less than 45 mins, whereas the drying-type topping compound dries over a 16 - 24 hour period.

Referring now to Figure ID, once the topping compound 16 has set or dried sufficiently, it is then surface finished, such as being hand-sanded with sandpaper S or electric sander.

In the case of a setting-type topping compound, if the base coat 12, with embedded tape 14 and topping compound 16, have been applied in the morning, and the topping compound has set sufficiently, the hand-sanding with sandpaper S or electric sander can advantageously take place in the afternoon of the same day.

In the case of a drying-type topping compound, if the base coat 12, with embedded tape 14 and topping compound 16, have been applied in the morning, and the topping compound has dried sufficiently, the hand-sanding with sandpaper S or electric sander can take place in the morning of the next day.

In either case, the set or dried and surface-finished joint can advantageously be painted on the next day.

Figure 1E shows a cross-sectional plan view taken through the resultantjoint to illustrate the embedded tape and compounds 12 and 16. Laboratory results indicate that the resultant joint compares favourably with existing joints that have been formed in accordance with a three coat, prior art methodology.

Example 2 - Formulation for Base Coat

The base coat formulation comprised a fine aridized plaster (- 78 wt. %) which, together with several organic binders, was observed to provide sufficient hardness and strength to the base coat once set (i.e. the base coat employed more binder than in comparison to the topping compound - see Example 3).

The base coat also comprised three types of fillers (two mineral fillers and an inert, lightweight filler) in an appropriate proportion (i.e. less in comparison to the topping compound), namely: calcium carbonate (CaCO 3), perlite microspheres, and mica. The CaCO3 (- 11 wt. %) provided body/bulk to the base coat. The CaCO3 grade was Microfine at an average particle size of around 5 microns and so added a smooth, grit-free consistency to the base coat. The perlite microspheres (at ~ 3.9 wt. %) reduced the shrinkage and density (weight) of the compound and thus increased its ease of handling, and also improved the rheology of the base coat. The mica (at ~ 3.7 wt. %) provided good mix-ability and crack resistance to the base coat.

The base coat further comprised a clay, namely, attapulgite (e.g. PalyGel*, MIN-U-GEL*, etc). The attapulgite provided a thickening function, improved the rheology and reduced the need for an additional amount of cellulosic agents.

The base coat also comprised cellulosic thickeners, namely, hydroxy propyl methyl cellulose (HPMC) and modified cellulose ether (MHEC) as water retainers/thickeners (at less than ~ 0.6 wt. % in total). Limiting the cellulosics to less than 0.6% by weight of the compound limited the amount of air entrainment during formulation/mixing of the base coat (i.e. avoiding the need for anti-foaming agents), and at this level did not impede workability and use of the base coat. Also, at a level of cellulosics > 0.6 wt. %the base coat becomes sticky (i.e. harder to apply, sticking to the jointing tools, etc.). At this level the cellulosics retained sufficient water, and provided a sufficient amount of thickening, to facilitate smooth and easy trowelling of the base coat with the jointing tools.

The base coat further comprised polymeric binders, namely: ethylene vinyl acetate (EVA) powder (- 1.3 wt. %); modified starch as an adhesive/gum (e.g. Tackidex© 250, at ~ 0.5 wt. %); polyvinyl alcohol (PVA) to provide both a binding and thickening function (at ~ 0.15 - 0.8 wt. %); and potato starch ether for rheology modification and thickening (e.g. Solvitose* FC50, at ~ 0.1 wt. %). The EVA helped to bind together (i.e. during curing) all of the components, as well as to promote good adhesion properties of the compound to plasterboard/wallboard substrates. In some embodiments of the base coat compound, the higher levels of PVA were employed and the starch(es) were removed from the formulation.

A fungicide was also added to the compound to control bacterial, algal and fungal growth therein, to improve in situ life of the base coat and to protect paint films applied over the joint. The fungicide added was a dithiocarbamate (e.g. Ziram®, at ~ 0.12 wt. %).

Sorbitol (or mannitol) (at ~ 0.08 wt. %) was also added to the compound, being an amount to counteract the presence of boric acid (in the form of metal borate) in plasterboard. Otherwise, the metal borate would react with and coagulate the polyvinyl alcohol.

A dispersant such as a hydrophobic copolymer carboxylate polyelectrolyte (e.g. OrotanTM 731-DP at - 0.18 wt. %.) was added to help disperse all the components evenly throughout the wet compound during mixing with water. An accelerator (e.g. ground gypsum, such as SIA or CMA, at ~ 0.14 wt. %) and a retarder (e.g. an amino acid retarder, such as PlastRetard*, or hydrated lime and quartz mixed with proteinaceous material, such as Gold Bond* Retarder, at - 0.006 0.022 wt. %) were added to help control/regulate the base coat's initial setting time and hardening rate. The base coat also comprised skim milk powder (at ~ 0.175 wt. %) to retard the setting time and improve the rheology.

A hydrophobizing additive (e.g. a silane powder such as Elotex* Seal 712) was added (at 0.1 - 0.5 wt. %.) to increase water resistance of the base coat.

Preferred base coats had the following formulations:

Raw Material Description Fine Aridized 78.5 77.7 77.7 77.7 77.8 78.8 Plaster Calcium Carbonate 10.0 10.5 10.5 10.5 11.2 10.0 Microfine Perlite (Sil-Cell* 35/34 or Sil-Cell* 4.0 3.99 3.95 3.95 3.9 4 35 BC) Mica 150 3.33 3.33 3.33 3.29 3.7 3.13 Redispersible EVA 1.24 1.55 1.49 1.58 1.25 1.25 powder (DA-1100) Starch (Tackidex* - - 0.50 250) 25)- -

Attapulgite (PalyGel* or 0.734 0.754 0.78 0.79 0.25 0.75 MIN-U-GEL* 400) HPMC (Mecellose* 0.076 0.060 0.07 0.061 0.22 0.07 PMC 40 US) Skim Milk Powder 0.145 0.155 0.16 0.158 0.18 0.15 Dispersant (OrotanTm 731-DP) 0.124 0.129 0.13 0.132 0.18 0.12

Polyvinyl Alcohol 0.8 0.732 0.76 0.74 0.15 0.8 Accelerator (SMA 0.08 0.098 0.11 0.105 0.14 0.06 or CMA) Calcium hydroxide 0.038 0.038 0.040 0.040 0.12 0.1 (Hydrated Lime)

17493084_1 (GHMattes) P96139.AU.3

Fungicide (Ziram©) 0.12 0.12 0.12 0.121 0.12 0.12 Starch (Solvitose* - - - - 0.10 FC50) Sorbitol 0.3 0.3 0.29 0.29 0.08 0.3 Modified Cellulose 0.2 0.211 0.20 0.211 0.08 0.2 Ether MHEC Amino Acid 0.022 or 0.022 or 0.02 or as 0.02 or as Retarder as as required required 0.006 (PlastRetard* PE) required required Gold Bond* As Retarder required Hydrophobizing 0.311 0.311 0.29 0.29 - 0.31 Additive Total (approx.) 100 100 100 100 100 100

Base coat Formulations 1-6 as detailed above were found to have volume reductions during setting (shrinkage) of approximately 6.5%, as determined using a standard ring test method. This is in contrast to conventional, heavy setting-type base coat formulations (i.e. without lightweight fillers), which typically exhibit shrinkages of 8-9%.

The sandability of the of the base coat was assessed using a Taber Abrasion Resistance machine, with 105mm X 105mm base coat samples prepared and dried to constant weight at 21-25°C and 45-55% relative humidity. The samples were then weighed, subjected to sanding for 25 sanding revolutions at 500g abrading load, and re-weighed. The weight loss in grams then indicated the sandibility of the compound. Base coat Formulations 1-6 were found to have sandabilities of approximately 0.60g. This is in contrast to conventional, heavy setting-type base coat formulations (i.e. without lightweight fillers), which typically exhibit sandabilities of approximately 0.33g. In this regard, the lower the sandibility figure, the less is the sandibility of the formulation.

Example 3 - Formulation for Setting-type Topping Compound

The setting-type topping formulation also comprised a fine aridized plaster(~ 32 wt. %) which, together with several organic binders, provided sufficient setting and sufficient strength, whilst promoting ease of working and sand-ability/finishing (i.e. less binder than in comparison to the base coat - see Example 2). As noted above, the relatively lower proportion of plaster in the topping compound (as

17493084_1 (GHMattes) P96139.AU.3 compared to the base coat) contributed to improved sandability of the topping compound, providing for at least a Level 4 surface finish to be achieved in sanding.

The topping compound also comprised four filler materials (two grades of carbonate mineral filler, talc, and an inert, lightweight filler) in an increased proportion in comparison to the base coat. The fourfiller materials were: two grades (i.e. of different particle size) of CaCO3, perlite microspheres and talc.

A coarser grade CaCO3 (Circal 60/16 at ~ 26 - 36 wt. %) provided body/bulk to the topping. Afiner grade of CaCO3 (grade Microfine at an average particle size of around 5 microns) interspersed the coarser grade CaCO3 to add a smooth, creamy consistency to the topping.

The preferred inert, lightweight filler was again perlite microspheres (but at an increased level of - 5.5 wt. %), which again reduced the density (weight) of the topping and further increased its ease of handling, improved the rheology of the topping, and improved the sand-ability/finish-ability of the compound. As noted above, the combined effects of a lower proportion of plaster and a higher proportion of lightweight filler in the topping compound (as compared to the base coat) allowed for the dual purpose of maintaining sufficiently comparable shrinkage to the base coat (i.e. to prevent cracking during setting/drying for example), whilst providing for improved sandability, such that a joint having a Level 4 surface finish was able to be achieved within a single working day, using the two-coat method.

The talc (hydrated magnesium silicate at ~ 15 wt. %) replaced the mica of the base coat and provided additional body to the calcium carbonate, as well as itself providing good rheology, a smooth surface, good sand-ability and good paint-ability to the topping.

The topping additionally comprised potassium sulfate (at - 0.08 wt. %), an accelerator, to help catalyze the setting reaction of fine aridized plaster.

The other components of the topping compound as set forth below functioned in a similar manner to the base coat.

It was noted that the low shrinkage of the setting-type topping formulation was achieved due to crystal formation of the mineral (plaster) binder during the hydration reaction. A certain percentage of water in the prepared paste was consumed in the hydration reaction, which reduced the amount of free water for evaporation. The crystal structure of the mineral binder also helped to reduce shrinkage by inhibiting close packing of the inert fillers. The lightweight filler (e.g. perlite microspheres) also helped to reduce shrinkage when a proportion of the mineral (plaster) binder dried without setting.

Some preferred setting-type topping compounds had the following formulations:

Formulation 1 Formulation 2 Formulation 3 Raw Material Description (%) (%) (%) Fine aridized plaster 32.3 45.9 45.8 Calcium Carbonate 36.3 26.5 36.7 Microfine Calcium Carbonate 7.26 9.8 Perlite microspheres 5.5 5.5 5.5 Talc 14.7 8.8 8.9 Redispersible EVA powder 1.4 1.2 0.8 Attapulgite 1.1 0.7 0.7 HPMC 0.15 0.2 0.2 Modified Cellulose 0.42 Ether, MHEC 0.25 0.28 Poly Vinyl Alcohol 0.45 0.35 0.35 Sorbitol 0.15 0.16 0.11 Accelerator (SMA) 0.06 0.1 0.1 Retarder 0.05 0.06 0.06 Potassium Sulphate 0.08 0.2 0.39 Fungicide - 0.12 0.12 Skim Milk Powder - - 0.15 Calcium Hydroxide (hydrated 0.08 lime) - 0.05 Total (approx.) 100.0 100.0 100.0

Shrinkage 8.4 9.1 8.2 Sandability 1.81 1.35 1.4

Topping compound Formulations 1-3 as detailed above were found to have volume reductions during setting (shrinkage) of approximately 8.4%, 9.1% and 8.2% respectively, as determined using a standard ring test method at 23°C and 50% relative humidity. These shrinkages, while higher than that for the base coat compositions

17493084_1 (GHMattes) P96139.AU.3 comprising lightweight filler (approximately 6.5%), were found to be sufficiently comparable to that of the base coat to obviate cracking during completion of the two coat method.

The sandability of topping compound Formulations 1-3 (8.4, 9.1 and 8.2g, respectively) was found to be significantly higher (greater than double) than that for the base coat (0.6g) and thus suitable for achieving a Level 4 surface finish by sanding. This improvement in standability was noted to be due to the reduced proportions of calcium sulphate hemihydrate, and the increased proportions of lightweight filler (in this case perlite) in the topping compound formulations, as compared to of the proportions in the base coats.

The shrinkage and sandability results obtained for topping Formulations 1-3 indicated that each of the formulations was suitable to be used with any of the base coat formulations of Example 2, in successfully performing the two-coat jointing method within a single working day.

Again, shrinkage and sandability values were determined as described for Example 2.

Example 4 - Formulation for Topping Compound with Polymer Binder

The drying-type topping formulation comprised several organic binders, namely, EVA and PV Alcohol. These binders provided sufficient adhesion and strength, whilst promoting ease of working and sand-ability/finishing.

The drying-type topping formulation comprised a comparatively higher level of filler than the setting type formulation (i.e. ~ 55 wt. % or greater; CaCO3 at > 40 wt. %, talc at nearly 10 wt. %).

The drying-type topping formulation comprised a dispersant that was selected to disperse this comparatively higher level of filler in an aqueous phase of the topping compound (i.e. once formulated with the wet ingredients). The dispersant was selected from one or more of: a hydrophobic copolymer carboxylate polyelectrolyte (e.g. OrotanTM 731-DP); an ionic dispersant such as ammonium/sodium polyacrylate, or polyacylic acid; and/or a non-ionic dispersants such as a modified polyacrylate polymer, a modified polyurethane polymer, or an ethoxylate acetylene diols. The level of dispersant (- 0.03 wt. %) was selected to promote a low-shrinkage drying of the topping compound comparable to the base coat.

It was noted that low shrinkage in the drying-type (e.g. vinyl-based) topping compound was achieved due to the combination of higher filler content (or resulting low water content) and the lightweight filler, together with the dispersant, the latter which helped to achieve higher filler loading and to reduce water requirement (i.e. level of water required).

It was also noted that a further reduction of shrinkage was able to be achieved by employing a different EVA, such as DA-511 or Celvolit* 1309 at 2.07 wt. %, both of which require less water for formulating the topping. For example, these grades of EVA enabled a sacrificing of (reduction in) water down to ~ 35 wt. %.

Other factors which could be varied to control shrinkage of the drying-type topping formulation included varying the selected EVA properties, including:

- the molecular weight of polymer;

- the type and quantity of protective colloid used;

- its viscosity;

- the % of solids.

It was noted that Celvolit* 1309 has a lower viscosity (lower molecular weight) than the EVA of the formulation below (DA-511).

It was further noted that EVA polymers in emulsion form are stabilized using different type of protective colloids (such as polyvinyl alcohol, hydroxy-ethyl cellulose (HEC), starch, surfactants, etc). Polyvinyl alcohols used as a protective colloid are also of different types (e.g. different molecular weight, fully hydrolysed/partially hydrolysed, surface tension differences) which again was also noted to affect the water requirement. The employed grades of HEC could also have different molecular weights which could affect the water requirement.

A preferred drying-type topping compound had the following formulation:

Raw Material Description Formulation(%) Calcium Carbonate 47.1 Talc 8.30 Perlite microspheres 5.41 Attapulgite 1.42 Polyvinyl alcohol 0.3 Hydroxy Ethyl Cellulose 0.3 HPMC 0.15 Sorbitol 0.16 Dispersant 0.03 DRY INGREDIENTS TOTAL 63.16 (approx.) Water 34.6 EVA Emulsion 2.07 Biocide 0.17 WET INGREDIENTS TOTAL 36.84 (approx.) TOTAL (approx.) 100.0

Shrinkage 11.5 Sandability 2.4

Example 5 - Alternative Deployment of the Method & System

An alternative methodology for the jointing of adjacent, in situ building panels of plasterboard (or cellulose-cement boards) for walls and ceilings will now be described. In this embodiment, and in contrast to the embodiment shown in Figure 1, the reinforcing tape 14 is applied directly to the plasterboard at the joint J between the adjacent panels P of plasterboard. The reinforcing tape 14 may be in the form of an adhesive shrink-resistant glass fibre mat, such as various FibaTape products of St. Gobain (e.g. FibaTape Extra Strength Drywall Tape, FibaTape

Perfect Finish Ultra-thin Drywall Tape, FibaTape Mold-X1O Mold-Resistant Drywall Tape, FibaTape Standard Mesh Drywall Tape, etc). The adhesive backing of the reinforcing tape 14 assisted in the correct positioning of the tape over the joint J, without the need to initially apply a base coat 12 to the joint.

A thin layer of a setting type base coat 12 was then applied over the reinforcing tape 14 using a suitably bladed tool B (e.g. broad-knife or trowel). This first application of the base coat 12 was applied so as to infuse through the tape 14 and fill the recess R between the adjacent panels.

Once the base coat 12 had set sufficiently (e.g. ~ 75 minutes after first being applied), a setting or drying type topping compound 16 was applied (e.g. with a trowel T) and was allowed to set or dry. The setting-type topping compound can also be formulated to initially set in about a 45 - 60 minute interval, whereas the drying-type topping compound is usually formulated to dry over a 16 - 24 hour period.

Once the topping compound 16 had set or dried sufficiently, it was then surface finished, such as being hand-sanded with sandpaper S or an electric sander. If, for example, the tape 14, base coat 12 and setting-type topping compound 16 have been applied in the morning, the system and method are such that the topping compound 16 has set sufficiently so that the hand-sanding with sandpaper S or electric sander can take place in the afternoon of the same day. If a drying-type topping compound is used, and the topping compound has dried sufficiently, the hand-sanding with sandpaper S or electric sander can take place in the morning of the next day.

Whilst a number of specific method and system embodiments have been described, it should be appreciated that the method and system may be embodied in other forms.

In the claims which follow and in the preceding summary except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", that is, various features may be associated with further features in various embodiments.

Variations and modifications may be made to the parts previously described without departing from the spirit or ambit of the disclosure.

Claims

1. A two-coat method for the jointing of adjacent, in situ plasterboard building panels, the two-coat method comprising:

applying a base coat at a joint of the adjacent panels and allowing it to set, the base coat formulated to be of a setting type and comprising calcium sulphate hemihydrate and a lightweight filler material;

applying a topping compound over the set base coat and allowing it to set, the topping compound also formulated to be of a setting type and comprising calcium sulphate hemihydrate and a lightweight filler material, the topping compound being formulated to have a proportion of calcium sulphate hemihydrate that is less than in the base coat; and

sanding the set topping compound so as to achieve at least a Level 4 surface finish.

2. A method as claimed in claim 1, wherein, each of the base coat and topping compound comprises a beta-calcium sulphate hemihydrate.

3. A method as claimed in claim 1 or 2, wherein each of the base coat and topping compound is formulated to have a short setting time.

4. A method as claimed in claim 3, wherein each of the base coat and the topping compound it is formulated to have a setting time of approximately 45-60 minutes.

5. A method as claimed in any one of the preceding claims, wherein the proportion of lightweight filler material in the base coat is less than that in the topping compound.

6. A method as claimed in claim 5, wherein the lightweight filler material comprises perlite microspheres.

7. A method as claimed in any one of the preceding claims, wherein each of the base coat and the topping compound comprises a metal carbonate-based material such as calcium carbonate.

8. A method as claimed in any one of the preceding claims, wherein each of the base coat and the topping compound further comprises a filler, such as talc or mica, to improve rheology and sand-ability.

9. A method as claimed in any one of the preceding claims, further comprising a water soluble or dispersible polymeric binder.

10. A method as claimed in claim 9, wherein the water soluble or dispersible polymeric binder comprises one or more of:

polyvinyl alcohol; starch; a polymer emulsion of: ethylene vinyl acetate; polyvinyl acetate; acrylic; polyacrylamide; styrene acrylic; styrene butadiene rubber.

11. A method as claimed in any one of the preceding claims, wherein the base coat is applied together with a reinforcing tape that is embedded so as to cover the joint, prior to setting of the base coat.

12. A two-coat system for the jointing of adjacent, in situ plasterboard building panels, the system comprising:

- a base coat which is formulated as a setting type compound to be applied at a joint of the adjacent panels and allowed to set, the base coat comprising calcium sulphate hemihydrate and a lightweight filler material;

- a topping compound which is formulated as a setting type compound to be applied over the base coat and allowed to set, the topping compound comprising calcium sulphate hemihydrate and a lightweight filler material, the topping compound being formulated to have a proportion of calcium sulphate hemihydrate that is less than in the base coat and to achieve at least a Level 4 surface finish when sanded.

13. A system as claimed in claim 12, the system further comprising a reinforcing tape that is to be embedded into the base coat to cover the joint.

14. A system as claimed in claim 11 or 12, wherein the base coat is formulated such that, after application at the joint, it sets within approximately 75 min, and wherein the topping compound is formulated such that, after application over the set base coat, it sets within approximately 75 min.

15. A system as claimed in claim 14, wherein the topping compound is able to be applied to the base coat approximately 75 min after the base coat has first been applied.

16. A system as claimed in any one of claims 12 to 15, wherein the base coat and topping compound are formulated in a manner as set forth in any one of claims 2 to 10.