NZ714106B2 - Improved 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 base coat compound of the setting-type, comprising 70 – 80 wt. % of a mineral binder, 15 – 25 wt. % of a filler material, 1 – 3 wt.% of an organic binder and 0.1% to 0.5%, by weight, of a hydrophobizing additive. 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 base coat compound is strong and lightweight, with low shrinkage. n organic binder and 0.1% to 0.5%, by weight, of a hydrophobizing additive. 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 base coat compound is strong and lightweight, with low shrinkage.

Description

IMPROVED 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 base coat 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. 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 (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 good adhesion and strength, and low shrinkage. In this regard, it can be formulated using hemihydrate 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 trowelled), high sand-ability (i.e. 17801745_1 (GHMatters) P97043.NZ 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 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 base coat compound for the jointing of adjacent, in situ building panels. The base coat compound is formulated to be of a setting type and the building panels may be plasterboard or cellulose-cement board.

The base coat compound can be formulated to have a short initial setting time (e.g. 20 – 60 minutes) to be ready for application of a topping compound after 30 – 75 minutes. For example, the base coat compound can be formulated with an accelerator and/or retarder to provide a full hydration time of approximately 30 – 75 minutes, thereafter, a topping may be applied 30 – 75 minutes after first application of the base coat compound.

The fast setting base coat compound allows for the possibility of a joint to be surface finished in a single working day (e.g. ready for painting the next day). The ability to fix panels and complete the jointing of them in one working day, and paint them the next represents a significant advance in the art, and substantially increases 17801745_1 (GHMatters) P97043.NZ building productivity.

The base coat compound can comprise 70% to 80%, by weight, of a mineral binder, such as a non-hydraulic binder. The mineral binder can, for example, comprise calcium sulphate hemihydrate (e.g. beta-calcium sulphate hemihydrate due to its availability, ease of processing and ease of handling). The mineral binder can provide strength to the base coat compound.

The base coat compound can also comprise 15% to 25%, by weight, of a filler material. The 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 another type of mineral filler material. The filler material can provide some bulk to the base coat and improve its mixing, handling and spreadability.

In one embodiment the metal-carbonate based filler material may comprise % to 12%, by weight, of calcium carbonate; the lightweight filler material may comprise 3% to 5%, by weight, of e.g. perlite microspheres; and the mineral filler material may comprise 3% to 4%, by weight, of mica.

The base coat compound can further comprise 1% to 3%, by weight, of an organic binder. The organic binder can also provide strength to the base coat compound, and can help bind together various components of the base coat compound. The organic 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; styrene butadiene rubber.

In one embodiment the organic binder may comprise 1% to 2%, by weight, of ethylene vinyl acetate and 0.1% to 1%, by weight, of polyvinyl alcohol. In other embodiments, the binder may further comprise one or more starches. In embodiments that include starch, other components of the binder may be reduced (e.g. the amount of polyvinyl alcohol may be reduced to accommodate the inclusion of starch as a binder).

The base coat compound can further comprise 0.1% to 0.5%, by weight, of a hydrophobizing additive. 17801745_1 (GHMatters) P97043.NZ In one embodiment the hydrophobizing additive may comprise silane.

The base coat compound can additionally comprise one or more thickening agents. For example, the one or more thickening agents may comprise a clay (e.g. 0.2% to 0.8%, by weight, of attapulgite or bentonite) and one or more cellulosic thickeners (e.g. HPMC at 0.05% to 0.25%, by weight, and MHEC at 0.05% to 0.3%, by weight).

The base coat compound may be formulated so as to be applied together with a reinforcing tape. In one embodiment, the reinforcing tape may be embedded in the base coat compound prior to setting of the base coat, so as to cover the joint. In another embodiment, 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. The reinforcing tape can be formed from a material that is resistant to swelling and shrinkage during wetting and drying (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 base coat 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 base coat 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 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, 17801745_1 (GHMatters) P97043.NZ separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure.

The base coat compound 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 base coat compound is formulated to provide underlying joint strength whilst having low shrinkage and good adhesion to the tape. It can be used with a topping compound or all-purpose compound that has good spread- ability, high sand-ability and a smooth surface finish once applied and sanded.

The base coat compound is of a setting type and is able to be rapidly deployed (e.g. as part of a single working day methodology). The base coat compound is formulated to have a short initial setting time (e.g. of approximately 20 – 60 min). In this regard, the base coat compound is formulated to set sufficiently such that, after application and sufficient hardening of the topping compound, and before 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 fix panels and complete the jointing in one working day, and paint them 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 compound comprises 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-calcium sulphate hemihydrate). The proportion of plaster used in the base coat compound is relatively high (e.g. 70 – 80 wt. %) because the base coat compound provides the underlying strength to the resultant joint, whereas a topping compound is formulated to enable its ease of application and surface finishing (e.g. sanding).

To enhance strength and adhesion, the base coat 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 butadiene 17801745_1 (GHMatters) P97043.NZ rubber, etc). Polyvinyl alcohol has the added benefit of providing a thickening function to the base coat.

Again, the proportion of both plaster setting agent and polymeric binder in the base coat is relatively high because the base coat provides the underlying strength in the resultant joint.

The base coat compound comprises 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 relatively low (e.g. less than in a topping compound) because the base coat comprises a relatively high level of hemi-hydrate plaster for strength and hardness.

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 (the topping compound may comprise talc). Mica in the base coat provides good mix- ability and crack resistance.

The filler material in the base coat 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 base coat compound prior to setting.

The base coat compound can also be formulated to adhere to and/or support therewithin a reinforcing tape (i.e. that is arranged along and is embedded in the base coat prior to its setting, thereby covering a central part of the joint). For example, the reinforcing tape may be applied (e.g. adhered) directly to the joint and the base coat compound may be applied thereover, or the reinforcing tape may be embedded in the base coat.

The reinforcing tape can be formed from a material that is resistant to swelling, shrinkage and deformation during wetting and drying (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 17801745_1 (GHMatters) P97043.NZ 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. Such a tape may have thicker fibres, to assist with adhesion between the base coat compound and the fibres in the reinforcing tape, to improve the strength of the resultant joint.

Example 1 – Formulation for Base Coat The base coat compound formulation comprised a fine beta-hemihydrate plaster (i.e. at a relatively high level of > 70 wt. % and up to 80 wt. %). A typical range for the plaster was ~ 77 – 79 wt. % which, together with several organic binders, was observed to provide sufficient hardness and strength to the base coat compound once set.

The base coat compound was formulated to enable it to rapidly set (e.g. as part of a single working day methodology). The base coat was formulated to have as short an initial setting time as workable, e.g. of approximately 45 – 60 min. In this regard, the base coat was formulated to set sufficiently such that the topping compound could be applied thereto after around 60 – 75 minutes from application.

This allowed the joint to be surface finished (e.g. sanded) before the end of a working day.

To help facilitate the control of formulation set, an accelerator (e.g. ground gypsum, such as SMA or CMA, in a range of 0.05 to 0.15 wt. %) and a retarder (at ~ 0.005 to 0.04 wt. %) were added. These helped to control/regulate the base coat’s initial setting time and hardening rate. The retarder itself either comprised an amino acid (e.g. PlastRetard at ~ 0.006 to 0.022 wt. %), or a retarder comprising hydrated lime and quartz mixed with proteinaceous material (e.g. Gold Bond Retarder). The 17801745_1 (GHMatters) P97043.NZ base coat also comprised skim milk powder (at ~ 0.1 to 0.2 wt. %) to help retard the setting time and improve the rheology of the base coat compound.

The base coat compound further comprised three types of filler (two, different, mineral fillers and an inert, lightweight filler) in an appropriate proportion (i.e. less in comparison to a topping compound), namely: calcium carbonate (CaCO ), perlite microspheres, and mica. The CaCO (~ 10 – 11 wt. %) provided body/bulk to the base coat. The CaCO 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 – 4 wt. %) reduced the 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 – 4 wt. %) provided good mix-ability and crack resistance to the base coat.

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

The base coat also comprised cellulosic thickeners, namely, hydroxy propyl methyl cellulose (HPMC) at ~ 0.05 to 0.25 wt. % and modified cellulose ether (MHEC) at ~ 0.05 to 0.3 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 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 compound. Also, at a level of cellulosics > ~ 0.6 wt. %, the base coat 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 base coat compound with the jointing tools.

The base coat compound 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, 17801745_1 (GHMatters) P97043.NZ 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. Orotan 731-DP at ~ 0.1 – 0.2 wt. %.) was added to help disperse all the components evenly throughout the wet compound during mixing with water.

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

Base Coat Formulations Six preferred base coat compounds had the following formulations, with Formulations 1 and 2 being most preferred: Raw Material Description 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) 17801745_1 (GHMatters) P97043.NZ Formulation 1 (%) Formulation 2 (%) Formulation 3 (%) Formulation 4 (%) Formulation (%) Formulation 6 (%) 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 - - - - 0.50 - (Tackidex 250) Attapulgite (PalyGel or MIN- 0.734 0.754 0.78 0.79 0.25 0.75 U-GEL 400) HPMC (Mecellose 0.076 0.060 0.07 0.061 0.22 0.07 PMC 40 US) 0.145 0.155 0.16 0.158 0.18 0.15 Skim Milk Powder Dispersant 0.124 0.129 0.13 0.132 0.18 0.12 (Orotan 731-DP) 0.8 0.732 0.76 0.74 0.15 0.8 Polyvinyl Alcohol Accelerator 0.08 0.098 0.11 0.105 0.14 0.06 (SMA or CMA) Calcium hydroxide 0.038 0.038 0.040 0.040 0.12 0.1 (Hydrated Lime) 0.12 0.12 0.12 0.121 0.12 Fungicide (Ziram ) required Starch - - - - 0.10 - (Solvitose FC50) Sorbitol 0.3 0.3 0.29 0.29 0.08 0.3 Modified Cellulose MHEC (Walocel 0.2 0.211 0.20 0.211 0.08 0.2 MKX 25000 PP20) Amino Acid 0.022 or 0.022 or 0.02 or as 0.02 or as Retarder as as 0.006 - required required (PlastRetard PE) required required Gold Bond As - - - - - Retarder required Silane 0.311 0.311 0.29 0.29 - 0.31 (Elotex Seal 712) 100 100 100 100 100 100 Total (approx.) Each of the Formulations gave a base coat compound that, as a result of the inclusion of a lightweight filler, was lightweight and that had low shrinkage.

As identified above, different types of lightweight filler, such as various ® ® ® types of perlite (Sil-Cell 35/34 or Sil-Cell 35 BC) can be used. Sil-Cell 35/34 is a perlite that has been coated with silane, whereas Sil-Cell 35 BC is an uncoated perlite. The use of an uncoated perlite improved the mixability and dispersion of the perlite when the compound was mixed with water (i.e. immediately prior to 17801745_1 (GHMatters) P97043.NZ application of the base coat compound). Nonetheless, a silane coated perlite was also suitable.

The inclusion of perlite can sometimes produce marginally more pin-holing, which is caused by water seeping into pores and air pushing out. However, the use of a hydrophobizing additive, such as silane, in the base coat compound can counter this shortcoming. The use of a hydrophobic dispersant can further assist in preventing pin-holing. Both of these additives assist in keeping water on the base coat compound’s surface so that the water evaporates rather than migrating into the base coat compound and causing pin-holing.

Example 2 – Deployment of the Base Coat 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 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.

In a variation as set forth in Example 3, 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 usually takes place over a 45 – 60 minute interval). 17801745_1 (GHMatters) P97043.NZ 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 (as appropriate). 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 will dry 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. If, for example, the base coat 12, with embedded tape 14 and setting-type topping compound 16 have been applied in the morning, the system and method are such that the topping compound has set sufficiently so that the hand- sanding with sandpaper S or electric sander can take place in the afternoon.

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.

Figure 1E shows a cross-sectional plan view taken through the resultant joint to illustrate the embedded tape and compounds 12 and 16.

In the case of a drying-type compound, if the base coat 12, with embedded tape 14 and drying-type 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.

Whether using a setting or drying-type topping compound, the set or dried and surface-finished joint can advantageously be painted on the next day.

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 3 – Alternative Deployment of the Base Coat 17801745_1 (GHMatters) P97043.NZ 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, the reinforcing tape is applied directly to the plasterboard at the joint between the adjacent panels of plasterboard. The reinforcing tape 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- X10 Mold-Resistant Drywall Tape, FibaTape Standard Mesh Drywall Tape, etc).

The adhesive backing of the reinforcing tape assisted in the correct positioning of the tape over the joint.

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

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

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

Whilst a number of specific base coat compound embodiments have been described, it should be appreciated that the compound may be embodied in other forms. 17801745_1 (GHMatters) P97043.NZ 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. 17801745_1 (GHMatters) P97043.NZ

Claims (18)

1. A base coat compound for the jointing of adjacent, in situ building panels, the base coat compound being of a setting type and comprising: − 70% to 80%, by weight, of a mineral binder; − 15% to 25%, by weight, of a filler material; − 1% to 3%, by weight, of an organic binder; and − 0.1% to 0.5%, by weight, of a hydrophobizing additive.

2. A base coat compound as claimed in claim 1, wherein the base coat compound is formulated to have a setting time of 20-75 minutes.

3. A base coat compound as claimed in claim 2, wherein the base coat compound is formulated with an accelerator and/or retardant to have a setting time of approximately 45 – 60 min.

4. A base coat compound as claimed in any one of the preceding claims, wherein the mineral binder is a non-hydraulic binder.

5. A base coat compound as claimed in any one of the preceding claims, wherein the mineral binder comprises calcium sulphate hemihydrate.

6. A base coat compound as claimed in any one of the preceding claims, wherein the mineral binder comprises beta-calcium sulphate hemihydrate.

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

8. A base coat compound as claimed in claim 7, wherein the filler material comprises a metal-carbonate based filler material, a lightweight filler material and a mineral filler material.

9. A base coat compound as claimed in claim 8, wherein: - the metal-carbonate based filler material comprises 10% to 12%, by weight, of calcium carbonate; 17801745_1 (GHMatters) P97043.NZ - the lightweight filler material comprises 3% to 5%, by weight, of perlite microspheres; - the mineral filler material comprises 3% to 4%, by weight, of mica.

10. A base coat compound as claimed in any one of the preceding claims, wherein the organic binder comprises a water soluble or dispersible polymeric binder.

11. A base coat compound as claimed in claim 10, 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; or styrene butadiene rubber.

12. A base coat compound as claimed in claim 10 or 11, wherein the binder comprises 1% to 2% by weight, of ethylene vinyl acetate and 0.1% to 1%, by weight, of polyvinyl alcohol.

13. A base coat compound as claimed in any one of the preceding claims wherein the hydrophobizing additive comprises silane.

14. A base coat compound as claimed in any one of the preceding claims further comprising one or more thickening agents.

15. A base coat compound as claimed in claim 14, wherein the one or more thickening agents comprise a clay and one or more cellulosic thickeners.

16. A base coat compound as claimed in claim 15, wherein the clay comprises 0.2% to 0.8%, by weight, of attapulgite and, and where the cellulosic thickeners comprise HPMC at 0.05% to 0.25%, by weight, and MHEC at 0.05% to 0.3%, by weight.

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

18. A base coat compound as claimed in claim 17, wherein the reinforcing 17801745_1 (GHMatters) P97043.NZ