NZ714102A - Improved Jointing System - Google Patents

Abstract

A two-coat method for the jointing 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 comprising about 32-46 wt.% 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 to achieve at least a Level 4 surface finish. The method allows a second application of the base coat to be eliminated, yielding greater speed, reduced cost and reduced complexity.

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 nd to provide a smooth, easy-to-sand finish. The base coat is applied in two .

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 onal 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 rd (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 ng tape, and because it also provides the underlying joint strength n the adjacent , the base coat is formulated to have good adhesion to both board and jointing tape, te strength and low shrinkage. In this regard, it can be formulated using calcium sulphate hemihydrate plaster to set and harden vely quickly via a reaction with 18541106_1 ters) P96139.NZ water (a so-called "setting" compound). On the other hand, the topping compound es good spread-ability (i.e. easily trowelled), high sand-ability (i.e. easily sanded), and a good (e.g. ) surface finish once applied and sanded. In this regard, it can be formulated from a water-based ric 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 ng and finishing plasterboard sheets in which a tive material is first applied to securely join a side edge portion of a first plasterboard sheet to a side edge portion of a second rboard sheet. A joint filling compound is applied to overlie the connective material, and a ing compound is then d to overlie the joint filling compound. 526 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 ation 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 ose-cement board for walls and ceilings, etc). 18541106_1 (GHMatters) P96139.NZ The two-coat method comprises applying a base coat at a joint 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 are formulated to be of a setting type and comprise calcium sulphate hemihydrate and a lightweight filler material.

In accordance with the present disclosure, the two-coat method and system ing to the present sure 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 se m 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 g formulations may also serve to reduce age 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 ng and, particularly, ease of sanding. For example, the eight filler material may comprise perlite microspheres, or may comprise other lightweight fillers such as cenospheres, hollow glass microspheres, expanded silicates or ric pheres, 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 g ent (e.g. more beta-calcium sulphate hemihydrate) than the topping compound. In this way, the base coat can 18541106_1 (GHMatters) P96139.NZ 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, buting to an improved surface finish (i.e. allowing for at least a Level 4 surface finish).

In some ments, 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 ated whilst still achieving at least a Level 4 finish. This two-coat methodology can thus provide savings in time, cost and xity.

In a first form, and in contradistinction to the teaching in the art, each of the base coat and topping compound are ated to be of a setting type, the topping compound comprising about 32-46 wt. % calcium sulphate hemihydrate. 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 e in the art, and substantially increases building productivity.

In this first form, each of the base coat and topping compound comprise a plaster-based g compound, and each can be formulated to provide the able degree of shrinkage. In this regard, the plaster may comprise a betacalcium sulphate hemihydrate, the orm being of relatively low cost to e ed 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 is greater than that in the topping compound. This can result in the base coat providing adequate underlying wet th to the resultant joint during setting. The relatively lower proportion of plaster in the topping compound can also contribute to improved 18541106_1 (GHMatters) P96139.NZ 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 r and a higher tion of lightweight filler in the topping compound (as compared to the base coat) can e the dual purpose of ining 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 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. And for example, the topping compound can be formulated to have an initial setting time of approximately 45 – 60 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 e 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 tion 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 th and adhesion, thus providing underlying th to the resultant joint, s 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 able to the base coat. 18541106_1 (GHMatters) P96139.NZ In this second form, each of the base coat and topping compound can comprise a water e 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 e or dispersible polymeric binder may comprise one or more of: nyl alcohol, , a polymer emulsion of: ethylene vinyl acetate; nyl acetate; acrylic; polyacrylamide; styrene acrylic; styrene butadiene rubber.

In this second form, the drying type formulation of the topping compound can se 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 um/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 lowshrinkage drying of the topping nd 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. g). 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 nd.

For example, the base coat can comprise more of the mineral binder (e.g. more betacalcium 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 e for ease of handling, ease of spreadability, and ease of sanding. 18541106_1 (GHMatters) P96139.NZ In one embodiment of either the first or second form, the filler 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 nd may se 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 g compound, without compromising joint th. Such a al can further e 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 pheres) 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 d (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 g compound is d, d to set or dry, and is then surface ed (e.g. sanded). With the first form of the present method and system, this can all take place in one working day. 18541106_1 (GHMatters) P96139.NZ In some embodiments of either the first or second form, an adhesive reinforcing tape may be applied directly to the joint of the adjacent panels, prior to applying the base coat.

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 g 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 th of the joint. Such a tape may have r fibres, to assist with adhesion between the base coat and the fibres in the reinforcing tape, to e the strength of the resultant joint. A glass fibre tape can also help to reduce blisters/bubbles in the joint (which is a known m 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 g compound to be applied over the base coat and d 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 twocoat system can be deployed quickly (e.g. in one single working day), representing a significant e in the art. 18541106_1 (GHMatters) P96139.NZ 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 an adhesive reinforcing tape. The adhesive reinforcing tape may be applied (e.g. adhered) directly to the joint and the base coat may be applied thereover. In some embodiments, 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 material. 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, and is iently set (i.e. for application of the topping nd) after approximately 75 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 l setting time of approximately 45 – 60 min. For example, and as set forth above, the topping compound may be applied to the base coat, incorporating the reinforcing tape, approximately 75 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 nd has set and sufficiently dried, it can, for example, be surface finished (e.g. sanded) on the same g 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 ng panels (e.g. building panels of rboard for walls and ceilings, etc). The system employs a base coat which is ated 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, the g 18541106_1 (GHMatters) P96139.NZ compound comprising about 32-46 wt.% m 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 e at least a Level 4 surface finish when sanded.

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

BRIEF PTION 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.

ED DESCRIPTION OF SPECIFIC EMBODIMENTS In the ing 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 y 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 /panels of plasterboard and ose-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. 18541106_1 (GHMatters) P96139.NZ 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 ility 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, able to the base coat.

First Mode Each of the base coat and topping nd is formulated to be of a setting type, whereby they have comparable degrees of shrinkage. In addition, the method and system can be y 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 surface finished (e.g. ), whereby the joint is ready for painting the next day. The ability to fix boards and te 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 ry.

For use with plasterboard and cellulose-cement board, optimally the base coat and topping compound each comprise a r-based, setting nd. 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 ation and surface finishing (e.g. sanding).

To enhance strength and adhesion, each of the base coat and topping nd further comprise a water soluble or dispersible polymeric binder, optimally including ethylene vinyl acetate and polyvinyl alcohol (although other 18541106_1 (GHMatters) P96139.NZ suitable binders include starch, nyl acetate; c; polyacrylamide; styrene acrylic; styrene butadiene rubber, etc.).

The proportion of both r 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 resultant joint. r, 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 ated 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 d in one working day).

In this regard, because the topping nd 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 se productivity in the building industry.

In the second mode, the base coat is formulated as in the first mode, to provide the ying strength to the resultant joint. 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 06_1 ters) P96139.NZ polymeric binder. Optimally the polymeric binder includes ethylene vinyl acetate and nyl alcohol (although other suitable binders include starch, polyvinyl acetate; acrylic; polyacrylamide; styrene acrylic; styrene butadiene rubber, etc).

Polyvinyl alcohol has the added benefit of ing 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 carbonatebased material (e.g. calcium carbonate). The proportion of filler material in the base coat is less than in the topping nd because the base coat comprises more binder than the topping compound. The greater amount of filler in the topping compound enhances ease of ng, ease of spreadability, and ease of sanding.

The filler material also includes a filler that improves rheology and sandability 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 nd provides good gy to the compound during its application and good bility 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 th. The lightweight filler material can also increase ease of handling. For example, the lightweight filler material can be perlite pheres or can be other lightweight fillers such as cenospheres, hollow glass pheres, expanded silicates or polymeric microspheres, etc. Such lightweight fillers can also help to reduce age of each of the base coat and topping compound prior to setting. 18541106_1 (GHMatters) P96139.NZ 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 method and system employ a reinforcing tape that is arranged along and is ed 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 rcing tape is formed from a material that is resistant to swelling, shrinkage and deformation (e.g. glass fibre mat al in an elongate format). Such swelling can occur due to water absorption by some types of tape (e.g. . r, 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 h and between the fibres, and to fuse across the tape, which can further improve the strength of the joint. 18541106_1 (GHMatters) P96139.NZ 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 ose-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 l part of the joint J using a suitably bladed tool (e.g. broad-knife or trowel) B.

Figure 1B shows a r 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 1C, once the base coat has set sufficiently (e.g. ~75 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, whereas the drying- type topping compound dries over a 16 – 24 hour period.

Referring now to Figure 1D, 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 g 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 anding with sandpaper S or ic 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 06_1 (GHMatters) P96139.NZ the topping compound has dried sufficiently, the anding with sandpaper S or electric sander can take place in the morning of the next day.

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

Figure 1E shows a sectional plan view taken through the resultant joint to illustrate the embedded tape and compounds 12 and 16. Laboratory results te 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 sed 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 (CaCO3), 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 gy of the base coat. The mica (at ~ 3.7 wt. %) provided good mix-ability and crack resistance to the base coat.

The base coat r 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 onal amount of cellulosic .

The base coat also comprised cellulosic thickeners, namely, hydroxy propyl methyl cellulose (HPMC) and modified ose ether (MHEC) as waterretainers /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 06_1 (GHMatters) P96139.NZ 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 osics > ~ 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 ties of the compound to plasterboard/wallboard substrates. In some embodiments of the base coat nd, the higher levels of PVA were employed and the starch(es) were removed from the ation.

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. %). ol (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 mer carboxylate ectrolyte (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 SMA or CMA, at ~ 0.14 wt. %) and a retarder (e.g. an amino acid retarder, such as PlastRetard®, or ed lime and quartz mixed with proteinaceous material, such as Gold Bond® er, 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. 18541106_1 (GHMatters) P96139.NZ A hydrophobizing additive (e.g. a silane powder such as ® 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: Formulation ( %) %) %) %) % % 1 Raw Material Formulation 2 ( Formulation ( 3 4 ( 5 6 Description Formulation Formulation Formulation Fine Aridized 78.5 77.7 77.7 77.7 77.8 78.8 Plaster Calcium Carbonate .0 10.5 10.5 10.5 11.2 10.0 Microfine Perlite (Sil-Cell® /34 or Sil-Cell® 4.0 3.99 3.95 3.95 3.9 4 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 dex® - - - - 0.50 - lgite (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 0.124 0.129 0.13 0.132 0.18 0.12 (OrotanTM 731-DP) 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) Fungicide (Ziram®) 0.12 0.12 0.12 0.121 0.12 0.12 Starch tose® - - - - 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 0.006 - ed required (PlastRetard® PE) required required Gold Bond® As - - - - - Retarder ed Hydrophobizing 0.311 0.311 0.29 0.29 - 0.31 Additive Total (approx.) 100 100 100 100 100 100 18541106_1 (GHMatters) P96139.NZ 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, ed sufficient setting and sufficient strength, whilst ing ease of working and sand-ability/finishing (i.e. less binder than in comparison to the base coat – see Example 2).

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

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

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 e, 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 r manner to the base coat.

It was noted that the low shrinkage of the setting-type topping formulation was ed 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 d the amount of free water for evaporation. The crystal structure of the mineral binder also helped to reduce 18541106_1 (GHMatters) P96139.NZ shrinkage by inhibiting close g of the inert fillers. The lightweight filler (e.g. perlite microspheres) also helped to reduce shrinkage when a proportion of the mineral er) binder dried without setting.

Some red setting-type topping compounds had the following formulations: Formulation 1 Formulation 2 Formulation 3 Raw al ption (%) (%) (%) Fine aridized plaster 32.3 45.9 45.8 m 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 rator (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 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 ing 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. %). 18541106_1 (GHMatters) P96139.NZ 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 nic 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 g compound comparable to the base coat.

It was noted that low shrinkage in the drying-type (e.g. vinyl-based) g 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 e higher filler g and to reduce water requirement (i.e. level of water required).

It was also noted that a further ion of shrinkage was able to be ed 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 age of the drying-type topping formulation included varying the ed 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 ) than the EVA of the formulation below (DA-511).

It was further noted that EVA polymers in emulsion form are ized using different type of protective colloids (such as polyvinyl alcohol, hydroxy-ethyl 18541106_1 (GHMatters) P96139.NZ cellulose (HEC), , surfactants, etc). Polyvinyl alcohols used as a protective colloid are also of different types (e.g. different lar , 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 ation: Raw Material Description Formulation (%) Calcium Carbonate 47.1 Talc 8.30 e microspheres 5.41 Attapulgite 1.42 Polyvinyl alcohol 0.3 Hydroxy Ethyl Cellulose 0.3 HPMC 0.15 Sorbitol 0.16 sant 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 Example 5 – Alternative Deployment of the Method & System An alternative methodology for the jointing of adjacent, in situ building panels of plasterboard (or ose-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 18541106_1 (GHMatters) P96139.NZ form of an adhesive shrink-resistant glass fibre mat, such as various FibaTape products of St. Gobain (e.g. FibaTape Extra th Drywall Tape, FibaTape Perfect Finish Ultra-thin Drywall Tape, FibaTape Mold-X10 Mold-Resistant Drywall Tape, FibaTape rd Mesh l Tape, etc). The adhesive backing of the reinforcing tape 14 ed 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 g 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 ation 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, s 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 anding with sandpaper S or electric sander can take place in the afternoon of the same day. If a -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.

In either case, the set or dried and surface-finished joint can advantageously be painted on 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. 18541106_1 ters) P96139.NZ In the claims which follow and in the preceding summary except where the context requires ise due to s 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. 18541106_1 (GHMatters) P96139.NZ

Claims (20)

1. A two-coat method for the jointing of adjacent, in situ plasterboard building panels, the at 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; ng a topping compound over the set base coat and allowing it to set, the g compound comprising about 32-46 wt.% 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 2, wherein each of the base coat and the topping compound is ated to have a g time of approximately 45-60 minutes.

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

5. A method as claimed in claim 4, wherein the lightweight filler material comprises perlite microspheres.

6. 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 al.

7. A method as d in any one of the preceding claims, wherein each of the base coat and the topping compound further comprises a filler material selected from talc or mica. 18541106_1 ters) P96139.NZ

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

9. A method as claimed in claim 8, n the water soluble or dispersible polymeric binder ses one or more of: polyvinyl alcohol; starch; a polymer emulsion of: ethylene vinyl acetate; polyvinyl acetate; acrylic; polyacrylamide; styrene acrylic; styrene butadiene rubber.

10. 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.

11. A method as claimed in any one of claims 1 to 9, wherein an ve reinforcing tape is applied directly to the joint of the adjacent panels, prior to applying the base coat.

12. A method as claimed in claim 10 or claim 11, wherein the reinforcing tape comprises a glass fibre mat material.

13. A two-coat system for the jointing of adjacent, in situ plasterboard ng 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 nd which is ated as a g type compound to be applied over the base coat and allowed to set, the g compound comprising about 32-46 wt.% 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.

14. A system as claimed in claim 13, the system further sing a reinforcing tape that is to be embedded into the base coat to cover the joint. 18541106_1 ters) P96139.NZ

15. A system as claimed in 13 the system r comprising an adhesive rcing tape that is to be applied directly to the joint of the adjacent panels, prior to applying the base coat.

16. A system as d in claim 14 or claim 15, wherein the reinforcing tape comprises a glass fibre mat material.

17. A system as claimed in any one of claims 13 to 16, 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.

18. A system as claimed in any one of claims 13 to 17, wherein the base coat and topping compound are formulated in a manner as set forth in any one of claims 2 to 12.

19. A two-coat method as claimed in claim 1, and substantially as herein described with reference to the accompanying drawings.

20. A two-coat system as claimed in claim 13, and substantially as herein described with reference to the anying drawings. 18541106_1 (GHMatters) P96139.NZ