NZ714105B2 - Jointing Compound - Google Patents

Abstract

improved jointing compound for the formation of a joint between adjacent, in situ panels of building material is disclosed. The improved jointing compound is a topping compound of the setting-type, comprising 30 – 47 wt. % of a mineral binder, 45 – 65 wt. % of a filler material, the filler material comprising a sand-ability modifying mineral filler material in an amount equivalent to 8% to 15%, by weight, of the topping compound, and 1 – 3 wt.% of an organic binder. The filler material may include at least two different filler materials, such as one or more mineral filler materials and a lightweight filler material. The topping compound is lightweight, with low shrinkage and provides good spread-ability, high sand-ability and a smooth surface finish once applied and sanded. ial comprising a sand-ability modifying mineral filler material in an amount equivalent to 8% to 15%, by weight, of the topping compound, and 1 – 3 wt.% of an organic binder. The filler material may include at least two different filler materials, such as one or more mineral filler materials and a lightweight filler material. The topping compound is lightweight, with low shrinkage and provides good spread-ability, high sand-ability and a smooth surface finish once applied and sanded.

Description

JOINTING COMPOUND TECHNICAL FIELD Disclosed is an improved jointing compound for the formation of a joint between adjacent, in situ panels of building material. The compound finds particular, though not exclusive, application as a topping compound in the jointing of plasterboard and cellulose-cement boards, and will primarily be described in this context.

BACKGROUND Plasterboard and cellulose-cement panels 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 (compound), jointing tape to hide the joint and a topping compound to hide the base coat and tape. The base coat is applied in two stages, a first to secure the tape therein, and a second to cover the tape.

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 (so-called "Level 4 finish"). To provide a surface finish that is sufficiently good for a so-called "Level 5 finish", a final skim or "finish" coat is thereafter applied over both joints and board.

Because the base coat is used together with the jointing tape, and because it also provides the underlying joint strength between the adjacent panels, it is formulated to have high strength, low shrinkage as well as good adhesion to the tape. In this regard, it can be formulated from plaster to set 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 troweled), 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.

US8257526 to the present applicant discloses a system of jointing and finishing 18034202_1 (GHMatters) P97042.NZ 2/09/21 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 sulphate, 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 compound as disclosed herein.

SUMMARY OF DISCLOSURE Disclosed herein is a topping compound formulation for the jointing of adjacent, in situ building panels (e.g. plasterboard or cellulose-cement board). In contradistinction to the prior art, the topping compound is formulated to be of a setting type to enable both fast setting as well as the possibility of a joint to be surface finished in a single working day (e.g. ready for painting the next). In this regard, the topping compound can set with sufficient strength and yet be appropriately constituted such that it can still be surface finished (e.g. to allow subsequent sanding of the joint) in one day.

The ability to clad and plaster a room in one working day, and paint it the next would represent a significant advance in the art, and could substantially increase building productivity.

To be of a stetting type, the topping compound can comprise 30% to 47%, by weight, of a mineral binder. The mineral binder can be a non-hydraulic binder, such as calcium sulphate hemihydrate (e.g. beta-gypsum hemihydrate due to its availability, ease of processing and ease of handling). Such a mineral binder can provide the requisite strength to the topping compound and, when appropriately formulated, can still be surface finished. 18034202_1 (GHMatters) P97042.NZ 2/09/21 The topping compound can also be formulated to have a short initial setting time of approximately 45 to 60 minutes (e.g. as quickly as 45 minutes). For example, the topping compound can be formulated with an accelerator and/or retarder to provide a full hydration time of approximately 45 – 60 min. For example, the topping compound may comprise 0.1% to 0.5%, by weight, of accelerator (such as SMA and potassium sulphate). The topping compound formulation is such that it may be applied in as little as 75 minutes after first application of a base coat.

The topping compound can also comprise 45% to 65%, by weight, of a filler material. The filler material can comprise a sand-ability modifying mineral filler material in an amount equivalent to 8% to 15%, by weight, of the topping compound.

The relatively higher level of filler material may be made up of at least two, different, filler materials. For example, the filler material may comprise a metal-carbonate based filler material, a lightweight filler material and a mineral filler material. The filler material provides bulk to the topping compound and improves its handling and spreadability, even where a setting-type binder is employed.

In one embodiment the sand-ability modifying mineral filler material may comprise talc, mica or a combination thereof.

In one embodiment the metal-carbonate based filler material may comprise 35% to 45%, by weight, of calcium carbonate; the lightweight filler material may comprise 1% to 6%, by weight, of e.g. perlite microspheres; and the mineral filler material may comprise 8% to 15%, by weight, of talc.

In one embodiment the filler material can comprise two grades of metal- carbonate based filler, namely, a coarser grade (e.g. 60/16 grade calcium carbonate at ~ – 40 wt. %) and a finer grade (e.g. Microfine grade calcium carbonate at ~ 5 – 10 wt. %; average particle size of around 5 microns). The finer grade can replace a corresponding proportion of the coarser grade such that the combined metal-carbonate based filler is approximately 35 – 45 wt. % of the topping compound.

The topping compound can further comprise 1% to 3%, by weight, of an organic binder. The organic binder can also provide strength to the topping compound, and can help bind together various of the components of the topping compound. The organic 18034202_1 (GHMatters) P97042.NZ 2/09/21 binder may comprise a water soluble or dispersible polymeric binder, for example, one or more of: polyvinyl alcohol; starch; a polymer emulsion of: ethylene vinyl acetate; polyvinyl acetate; acrylic; polyacrylamide; styrene acrylic; or styrene butadiene rubber.

In one embodiment the organic binder may comprise 0.8% to 1.8%, by weight, of ethylene vinyl acetate and 0.3% to 1.0%, by weight, of polyvinyl alcohol.

In one embodiment the topping compound may comprise a fungicide.

The topping compound can additionally comprise one or more thickening agents. For example, the one or more thickening agents may comprise a clay (e.g. 0.6% to 1.5%, by weight, of attapulgite) and one or more cellulosic thickeners (e.g. HPMC at 0.1% to 0.5%, by weight, and MHEC at 0.1% to 0.6%, by weight).

The topping compound may be formulated so as to be applied together with base coat. The base coat will typically comprise a reinforcing tape either embedded therein or underlying the base coat. The topping compound can be applied to cover the joint, after a predetermined amount of setting of the base coat (e.g. after ~ 75 minutes). The reinforcing tape employed with the base coat can be formed from a material that is resistant to swelling and shrinkage during setting and drying of the base coat (e.g. a glass fibre mat material of elongate format).

BRIEF DESCRIPTION OF DRAWINGS Notwithstanding any other forms that may fall within the scope of the topping compound 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, employing an embodiment of the topping compound.

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 18034202_1 (GHMatters) P97042.NZ 2/09/21 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.

The topping compound formulation 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).

In this regard, the topping compound is formulated to provide good spread- ability, high sand-ability and a smooth surface finish once applied and sanded.

The topping compound is of a setting type and is able to be rapidly deployed (e.g. as part of a single working day methodology). The topping compound is formulated to have a short initial setting time (e.g. of approximately 45 – 60 min). In this regard, the topping compound is formulated to set sufficiently such that, after application and sufficient set of the topping, and by the end of the working day, the joint is able to be surface finished (e.g. sanded). Thus, the surface-finished joint is ready for painting the next day. The ability to clad (i.e. fix panels) and plaster a room 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 topping compound formulation comprises a plaster-based setting compound. A preferred setting compound is beta-gypsum hemihydrate, because it has relatively low cost of production (i.e. compared to alpha-gypsum hemihydrate). The proportion of plaster used in the topping compound is formulated to enable its ease of application and surface finishing (e.g. sanding).

To enhance strength and adhesion, the topping compound further comprises an organic binder such as 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 18034202_1 (GHMatters) P97042.NZ 2/09/21 butadiene rubber, etc). Polyvinyl alcohol has the added benefit of providing a thickening function to the topping compound.

The topping compound further comprises a relatively high amount of filler material and, usually, a mix of at least two, different, filler materials. Typically a metal carbonate-based filler material (e.g. calcium carbonate) will form a major portion of the filler material mix. The filler material mix also includes a filler that improves slip/sand- ability such as talc or mica. More specifically, the topping compound comprises talc to provide good rheology, a smooth surface, good sand-ability and good paint-ability to the finished joint.

The filler material mix in the topping compound also comprises lightweight filler material to reduce its density 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 the topping compound.

The topping compound can also be formulated to cover a reinforcing tape (i.e. that is embedded in the base coat prior to applying the topping compound, thereby covering a central part of the joint). The reinforcing tape can be 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, synthetic fabric). Further, such shrinkage can occur during drying of some types of tape (e.g. paper, synthetic fabric). 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 topping, 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 to allow the base coat and or topping compound to permeate through and between the fibres, and to fuse across the tape, which can further improve the strength of the joint. 18034202_1 (GHMatters) P97042.NZ 2/09/21 Example 1 – Formulation for Topping Compound The topping compound formulation comprised a fine aridized plaster in a range of 30 – 47 wt. % (e.g. ~ 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 a base coat).

The topping compound also comprised four filler materials in a relatively higher range of 45 – 65 wt. % (i.e. than in comparison to a base coat). The filler materials preferably comprised two grades of carbonate mineral filler, talc, and an inert, lightweight filler, with the fillers being in an increased proportion in comparison to the base coat. This aided handling (i.e. trowel-ability, spread-ability, sand-ability, etc).

The preferred filler materials were: two grades (i.e. of different particle size) of calcium carbonate, perlite microspheres and talc.

A coarser grade CaCO (i.e. 60/16 at ~ 25 – 40 wt. %) provided body/bulk to the topping. When a finer grade of CaCO was employed (at ~ 5 – 10 wt. %, Microfine grade at an average particle size of around 5 microns) and the total calcium carbonate content (i.e. the finer and coarser grades combined) was 35 – 45 wt. %, with the finer grade of CaCO being interspersed with the coarser grade of CaCO to add a smooth, creamy consistency to the topping compound.

The preferred inert, lightweight filler was perlite microspheres at an increased level in a range of 1 – 6 wt. % (e.g. ~ 5.5 wt. %), which again reduced the density (weight) of the topping compound and further increased its ease of handling, improved the rheology of the topping compound, and improved the sand-ability/finish-ability of the compound.

The talc in a range of 8 – 15 wt. % (e.g. hydrated magnesium silicate at ~ 14.7 wt. %) 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 compound.

The topping compound additionally comprised the accelerator potassium sulphate (at 0.1 – 0.5 wt. %) to help catalyze the setting reaction of fine aridized plaster. 18034202_1 (GHMatters) P97042.NZ 2/09/21 Optionally, another accelerator (e.g. SMA – ground gypsum – in a range of 0.05 – 0.15 wt. %) was added. A retarder comprising an amino acid (e.g. PlastRetard ), or a retarder comprising hydrated lime and quartz mixed with proteinaceous material (e.g.

Gold Bond Retarder), at ~ 0.05 – 0.1 wt. % was added. The accelerator(s) and retarder helped to control/regulate the topping compound’s initial setting time and hardening rate.

Calcium hydroxide (hydrated lime at ~ 0.04 – 0.1 wt. %) was optionally added to control pH, improve workability and to help control setting characteristics.

The topping compound optionally also comprised skim milk powder (at ~ 0.1 – 0.2 wt. %) to help retard the setting time and improve the rheology.

The topping compound further comprised a clay, namely, attapulgite at ~ 0.6 – 1.5%, by weight. The attapulgite provided an additional thickening function and e.g. reduced the need for an additional amount of cellulosic agents. Alternatively, a clay such as bentonite can be employed.

The topping compound also comprised cellulosic thickeners, namely, hydroxy propyl methyl cellulose (HPMC at ~ 0.1 – 0.5 wt. %) and modified cellulose ether (MHEC at ~ 0.1 – 0.6 wt. %) as water-retainers/thickeners. Limiting the cellulosics to less than ~ 0.6% by weight of the compound limited the amount of air entrainment during formulation/mixing of the topping compound (i.e. avoiding the need for anti- foaming agents), and at this level did not impede workability and use of the topping compound. Also, at a level of cellulosics > ~ 0.6 wt. %, the topping compound became sticky (i.e. harder to apply, sticking to the jointing tools, etc). Thus, at this controlled level, the cellulosics retained sufficient water, and provided a sufficient amount of thickening, to facilitate smooth and easy trowelling of the topping compound with the jointing tools.

The topping compound further comprised polymeric binders in the weight range of 1 – 3 %, namely: ethylene vinyl acetate (EVA) powder (~ 0.8 – 1.8 wt. %); and polyvinyl alcohol to provide both a binding and thickening function (at ~ 0.3 – 1.0 wt.

%). The EVA helped to bind together (i.e. during curing) all of the components, as well 18034202_1 (GHMatters) P97042.NZ 2/09/21 as to promote good adhesion properties of the compound to plasterboard/wallboard substrates.

A fungicide may also be added to the topping compound to control bacterial, algal and fungal growth therein, to improve in situ life of the topping compound and to protect paint films applied over the joint. The fungicide added was a dithiocarbamate (e.g. Ziram , at ~ 0 – 0.2 wt. %).

Sorbitol (or mannitol) (at ~ 0.1 – 0.4 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.

Three topping compound embodiments had the following formulations, with Formulation 1 being preferred: 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 Ethylene Vinyl Acetate (Redispersible powder) 1.4 1.2 0.8 Attapulgite 1.1 0.7 0.7 HPMC 0.15 0.2 0.2 Modified Cellulose Ether, MHEC 0.42 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 lime) 0.08 - 0.05 Total (approx.) 100.0 100.0 100.0 18034202_1 (GHMatters) P97042.NZ 2/09/21 Example 2 – Deployment of the Topping Compound Figure 1 schematically depicts a methodology 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 base coat 12 (e.g. of a setting type) 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.

In a variation, an adhesive-backed reinforcing tape 14 can first be applied to cover the recess R at the joint J, and then the base coat 12 can be applied over the tape 14 using the bladed tool B. Where the tape comprises pores or is foraminous, the base coat can penetrate into and through the tape to fill the joint J.

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 typically 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 topping compound 16 is applied with a trowel T and is allowed to set. The topping compound is typically formulated to initially set in about a 45 – 60 minute interval.

Referring now to Figure 1D, once the topping compound 16 has set and dried sufficiently, it is then surface finished, such as being hand-sanded with sandpaper S or electric sander. If, for example, the base coat 12, with embedded tape 14 and topping compound 16 have been applied in the morning, the system and method are such that the topping compound has dried sufficiently so that the hand-sanding with sandpaper S or electric sander can take place in the afternoon. 18034202_1 (GHMatters) P97042.NZ 2/09/21 Figure 1E shows a cross-sectional plan view taken through the resultant joint to illustrate the embedded tape and compounds 12 and 16.

Advantageously, the methodology 10 is able to take place in one working day, representing a significant advance in the art. For example, steps 1A-1C can take place in the morning of a working day, and step 1D can take place in the afternoon of the same working day. Laboratory results indicate that the resultant joint compares favourably with existing joints that have been formed in accordance with a 2 day prior art methodology.

Whilst a number of specific topping compound embodiments have been described, it should be appreciated that the compound 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. 18034202_1 (GHMatters) P97042.NZ 2/09/21

Claims (8)

1. A topping compound for the jointing of adjacent, in situ building panels, the topping compound being of a setting type and comprising: 30% to 47%, by weight, of a mineral binder; 5 45% to 65%, by weight, of a filler material, the filler material comprising a sand- ability modifying mineral filler material in an amount equivalent to 8% to 15%, by weight, of the topping compound; and 1% to 3%, by weight, of an organic binder.

2. A topping compound as claimed in claim 1, wherein the sand-ability modifying 10 mineral filler material comprises talc, mica or a combination thereof.

3. A topping compound as claimed in claim 1 or 2, wherein the mineral binder comprises a non-hydraulic binder.

4. A topping compound as claimed in any one of the preceding claims, wherein the mineral binder comprises calcium sulphate hemihydrate. 15

5. A topping compound as claimed in any one of the preceding claims, wherein the mineral binder comprises beta-gypsum hemihydrate.

6. A topping compound as claimed in any one of the preceding claims wherein the filler material comprises at least two, different, filler materials.

7. A topping compound as claimed in claim 6, wherein the filler material further 20 comprises a metal-carbonate based filler material and a lightweight filler material.

8. A topping compound as claimed in claim 7, wherein: - the metal-carbonate based filler material comprises 35% to 45%, by weight, of calcium carbonate; and - the lightweight filler material comprises 1% to 6%, by weight, of perlite 25 microspheres. 18034202_1 (GHMatters) P97042.NZ