Water Resistant Plasterboard – wet area applications

BGC Plasterboard designed and developed WR Plasterboard for wet area walls, in residential and commercial buildings, such as bathrooms, laundries, toilets and cleaning room areas.

BGC WR Plasterboard has a low absorption core, eliminates the probability of water wicking, therefore preventing possible damage to the supporting structure and wall finishes.

Water Resistant Plasterboard:

  • Specifically designed for wet areas
  • Has a low absorption core
  • Light blue face for ease of identification
  • Quick and simple to install
Introduction

BGC Water Resistant (WR) plasterboard complies with the requirements of AS2588Gypsum Plasterboard’, (refer CSIRO Test Report DTS 713).

BGC Plasterboard designed and developed WR Plasterboard for wet area walls, in residential and commercial buildings, such as bathrooms, laundries, toilets and cleaning room areas.

BGC WR plasterboard is to be installed in accordance with AS 2589.1; 2007Gypsum Plaster Linings in Residential and Light Commercial Construction – Application and Finishes” and as detailed in AS 3740:2004Waterproofing of Wet Areas within Residential Buildings”.

BGC WR Plasterboard has a light-blue fungal resistant multi-layered facing board for easy identification. It is available in 10mm and 13mm thicknesses with recessed edges, ready for taping and jointing with proprietary water resistant stopping and setting compounds.

BGC WR Plasterboard has a low absorption core, eliminates the probability of water wicking, therefore preventing possible damage to the supporting structure and wall finishes.

Key Benefits

  • Cost effective, drywall wet-area lining system.
  • High serviceability performance board.
  • Dimensionally stable substrate for tiled wall finishes.
  • Ready for decorative paint and thin cover finishes.

Plasterboard Finish Selection

The selection of plasterboard finish in wet areas depends on the desired tiled surfaces and other wall decorations required. Generally, use Class 3 and 4 finishes in wet areas, as detailed in AS 2589.1-2007.

Where tiles are used, the finish can be of a lower standard and where other decoration is required, the standard is higher. BGC Plasterboard recommends the architect’s specifications for the level of finish required.

Early Fire Hazard Indices

BGC WR Plasterboard complies with AS 1530.3:1999

Ignitability                                          – 0
Spread of Flame Index                     – 0
Heat Evolved Index                           – 0
Smoke Developed Index                  – 4

Availability

BGC WR Plasterboard is available in 10mm and 13mm thicknesses, 1200mm and 1350mm wide and in various lengths.

BGC Plasterboard ensures that the range of stock sheet sizes listed are available, however variations may occur in some states.

Sheet Size

THICKNESS
(mm)
WIDTH
(mm)
 SHEET WIDTH (mm)
2400 2700 3000 3600 4200 4800 6000
10 1200 x x x x x x
1350 x x x x x
13 1200 x x x x
1350 x x x

Handling & Storage

Water Resistant Plasterboard should be stacked flat, up off the ground and supported on level, equally spaced (max 450mm) gluts.

Care should be taken to ensure edges of the Water Resistant Plasterboard are not damaged when handling.

Water Resistant Plasterboard should be delivered to site immediately prior to installation to reduce the risk of damage.

Installation

Install and fix BGC WR plasterboard sheets horizontally to minimise the number of joints and to minimise light reflections across the joints.

Cut the BGC WR Plasterboard from the face and snap back away from the score, then cut the back paper face toward the front face.

Use a straightedge for neat straight cuts.

Framing

Install and fix BGC WR plasterboard to timber or Cold Formed Steel (CFS) framing or furring channels, which satisfy the BCA requirements and which have been plumbed true and straight.

NOTE: Timber shall be kiln dried with a moisture content below 16%.

Prior to installing and fixing BGC WR Plasterboard, ensure that the preceding trades have certified, that –

  • Structural movement will not occur (or is minimised) at wall-to-wall and floor-to-wall junctions.
  • All noggings, trims and the like, are correctly installed and fixed for the bath, basins and other fixtures (Noggings are spaced at 600mm maximum centres for 10mm plasterboard and 800mm maximum centres for 13mm plasterboard).
  • All perimeters, corner and control joint flashings are in place and correctly installed.

Fixing

Fix BGC WR Plasterboard sheets horizontally to wall framing and or metal framing, with the bottom sheets first, at 6-10mm clear of the finished floor.

Set out sheets around all wall openings, with cutouts 200mm horizontally and 250mm vertically, to prevent corner cracking.

For untiled walls space fasteners at 600mm maximum centres on internal studs and at 150mm for internal and external corners. See Figure 1.

Press sheets firmly against the frame and fasten along one recessed edge at each framing member.

For all wet areas fasten sheets with corrosion resistant Class 3, or better screws, which comply with AS 3566:

For timber-framing plasterboard nails must comply with AS 2334; 1980 Steel Nails – Metric series and have a minimum Class 3 or better corrosion resistance.

BGC Plasterboard recommends the use of screw fasteners instead of nails.

Table 2- Minimum Screw Fastener Length and Type

SHEET THICKNESS CFS STEELUP TO 0.55 BMT CFS STEEL0.75 TO 1.1 BMT
10 mm 6-9 x 25 NP 6-18 x 25 SDP
13 mm 6-9 x 30 NP 6-18 x 30 SDP

NOTE: When fixing into preservative treated timbers, Class 3 AS 3566.2-2002 coatings of screws and nails are to be used.

NOTE: Do not fix BGC WR Plasterboard with adhesives.

Figure 1 – Sheet Set Out Untiled Areas

Tiled Walls

Position fasteners between 10mm and 16mm from the edge of the sheets at the correct spacing to carry the loads of the tiles.

For walls with tiles 6.5mm thick or 12.5 kg/m2 or less, space fasteners at 200mm maximum centres on the intermediate studs and at 150mm on internal and external corners, butt joints and around openings.

Where tiles are greater than 6.5mm thick or 32 kg/m2, space all fasteners at 100mm maximum centres in the centre of sheets, on internal and external corners, butt joints and around openings.

Tile adhesive should be compatible with the waterproofing membrane.

Pre-Formed Shower Base and External Shower Tray

Preliminary work and detail fixing out is similar for external shower trays and preformed shower bases, as shown in Figure 2.

Install and fix perimeter-flashing angles, at the wall/ floor junction and preformed shower bases or external shower trays, prior to fixing WR plasterboard lining.

Cut and install PVC corner angle, down inside the pre-formed shower base; Figure 8 and fasten to framing at 600m centres, in a staggered pattern.

Seal the lower edge of WR plasterboard sheets, whether cut or not, with a proprietary wet-area acrylic sealant to prevent potential moisture wicking.

Figure 2
Pre-Formed Shower Base and External Shower Tray – cont.
Install and fix sheets to the wall framing 6mm clear of the shower tray up-stand; See Figure 2 and of the mortar bed in the external shower tray.

Caulk the bottom edge of the sheets and the shower base or the mortar bed and around plumbing fixtures with a flexible sealant. See Figures 2 & 3.

Penetrations 

The WR Plasterboard must be cut out to leave a 6 mm gap all round the fixture. This gap must be filled with a mould resistant flexible sealant.

BGC recommends using a hole saw to make a neat cut out for fittings such as taps, shower roses etc. Do not use a hammer.

Additional framing must be installed as required to properly support all fixtures.
Figure 3 – Sealing Penetrations
Insitu Shower Tray
Install and fix perimeter-flashing angles, at the wall/floor junction.

Cut and install PVC corner angle and fasten to framing at 600m centres, in a staggered pattern.
Seal the lower edge of water resistant plasterboard sheets, whether cut or not, with a proprietary wet-area acrylic sealant to prevent potential moisture wicking.

Install and fix sheets to the wall framing, as outlined previously, 6mm clear off the floor.
Form a bond-breaker with closed-cell foam backing rod and masking tape at the bottom edge of the Plasterboard at wall/floor junction, as shown in Figure 4.

Caulk around plumbing penetrations and up the internal corners of the shower with flexible sealant.

Apply a proprietary liquid membrane material to the face of the plasterboard and floor to form an insitu internal shower tray.

Follow the membrane manufacturers’ instructions.

Apply the membrane to the vertical corner to a minimum height of 1800mm from the finished floor surface.

The liquid membrane is to extend 75mm minimum each side of the corner.

Note: Use only insitu membrane materials appraised and approved by recognised authorities.

Figure 4
Shower Over Bath

Preliminary work and fixing out detail is similar for preformed shower bases and in part the insitu tray details, see Figure 13.

Cut and install PVC corner angle, down inside the bath up-stand flange and fasten to framing at 600mm centres, in a staggerd pattern, see Figure 5.

Seal the lower edge of water resistant plasterboard sheets, whether cut or not, with a proprietary wet-area acrylic sealant, to prevent potential moisture wicking.

Install and fix sheets to the wall framing, as outlined previously 6mm clear off the bath up-stand.
Caulk the bottom edge of the sheets and the bath edge around plumbing fixtures with a mould resistant flexible sealant.

Apply a proprietary branded liquid membrane 150mm above the bath edge and wall surround, to a minimum height of 1800mm above the finished floor level and 75mm each side of the corner, see Figure 5 & 13.

Perimeter and Bath Flashing

Vertical corner is to angle finish inside perimeter wall angles and also pre-fabricated shower tray/base, insitu-laid trays or the like Refer Figure 5.

Figure 5

Structural Movements and Control Joints

Buildings and their component parts move over time due to various factors which may lead to building and or system failures if design, materials and installation are not satisfactory.

To minimise the risk of system failure take care when designing, detailing, installing and finishing all aspects of wet areas.

The design of wet areas must take into account any relative movements in the building structure and components, due to loading and temperature and humidity variations and the like. See Figure 6.

Figure 6

In long runs of wall, control joints should be set at 5.4 metres maximum in non-tiled areas, and at 4.2 metres maximum, in tiled areas or at construction joints, which ever is the lesser. Control joints must allow for the differential expansion and contraction between the structure, wall lining and tiles. Control joints, must be constructed with double studs, with a gap to suit the control joint type. Refer Figure 7.

Figure 7

Corner Jointing

Corners are set and finished with paper tapes in wet areas for internal corners, or casing beads for external corners.

However, in wet area construction, corners above pre-formed shower bases, insitu trays and shower over baths situations require special attention to detail, as noted.

Vertical Corner Flashing

In tiled walls, vertical corner flashings finish inside pre-fabricated shower tray/base, insitu-laid trays or the like. Refer Figure 8.

 Figure 8

Jointing

Wet area plasterboard joints must satisfy the BCA requirements and comply with AS 2589.1:2007

All WR plasterboard joints in wet areas must be set with perforated paper tapes and proprietary branded base and flushing compounds such as BGC WR Taping Cement.

The wet area base-coat system is typically a two-coat system under tiled areas and a three-coat system where tiles are not used.

All horizontal, vertical and corner joints and fastener points must, be stopped and set with the same materials, to ensure water resistance across the wall areas.

The use of correct materials, application and sequencing of taping and jointing is important and any deviation may result in joint failure.

Mixing of different proprietary compounds or application of setting type compounds over acrylic drying compounds, may lead to joint failure and will negate any proprietary item warranties.
Only use drying type topping or finishing compounds over water-resistant acrylic drying type base-coat compounds.

NOTE: Do not use setting type compounds over water-resistant acrylic drying type compounds.

Do not use self adhesive tapes.

Table 3 – Tiled Areas

First Coat Tape Second
Coat
Finish Coat
Water
Resistant
Taping
Cement
Paper Tape Water
Resistant
Taping
Cement
None
Required

Table 4 – Tiled Areas: – Non-Wet Areas

First Coat Tape Second
    Coat
Finish Coat
Water
Resistant
Taping
Cement
Perforated
Paper Tape
Water
Resistant
Taping
Cement
None
Required

Table 5 – Non-Tiled Areas: – Finish Coat

First Coat Tape Second
    Coat
Finish Coat
Water
Resistant
Taping
Cement
Paper Tape Water
Resistant
Taping
Cement
Water
Resistant
Taping
Cement

 First Coat and Tape

  • Wipe joint recesses with damp cloth to remove dust from plasterboard face.
  • Fully fill recess evenly with BGC WR Taping Cement.
  • Centrally bed the paper tape into bed coat and cover lightly with BGC WR Taping Cement compound and allow to fully dry.
  • Cover all fastener points with BGC WR Taping Cement compound and allow to fully dry.

 Figure 9

Second Coat

  • Apply the second coat of BGC WR Taping Cement compound, 180mm wide and feather out the edges and allow to fully dry.
  • Apply a second coat to all fastener points, feather out 25mm and allow to fully dry.
  • When the coating compounds are dry, lightly sand all joints and fastener points.

Figure 10

Finish Coat

The finish coat is only required where tiles are not used and another decorative finish is required.

  • Apply a 280mm wide approximate, thin finish coat, centrally over the second coat.
  • Dampen the outer edges with a sponge to feather out the edges of the finish coat and allow to dry.
  • Apply a thin finish coat over all fastener points and feather out 40mm and allow to dry.

Figure 11

Sanding and Finishing

  • Allow joint and fastener point coating compounds to dry for 24 hrs before sanding.
  • For tiled areas lightly sand all joints and fastener points, with 150 grit or with 220 sanding mesh, to remove any high spots.
  • Wipe off excess dust with a slightly damp cloth, prior to the application of tile adhesive, seal coats or decorative finishes.

Figure 12

Australian Standards

The following tables are the specific requirements for Wet Areas taken from the Australian Standards 3740-2004 and are applicable to areas lined with BGC WR plasterboard.

Wet Areas

An area within a building supplied with water from a water supply system and includes bathrooms, showers, laundries and sanitary compartments. Excludes kitchens, bar areas, kitchenettes or domestic food and beverage preparation areas”.

The BCA requires that all wet-area design, construction and materials, do not create unhealthy, dangerous conditions, or damage to building components, caused by dampness, water overflow, infiltration or penetration.

LEGEND:
N/A – Not Applicable / * Including mechanical fixings or fasteners through surface materials / ¥ Wall/floor junctions only / ‡Where floor waste is provided the floor shall be graded to the waste / §If a shower is included in a bath, include the requirements for shower area walls.

Figure 13

Table 6 – Design and Installation for Wet Area Waterproofing AS3740-2004

Vessels or area where the fixture is installed Level of risk Design and installation criteria
Floor Walls Junctions Penetration Figure No.
Shower area High Waterproofed
& drained
Water
resistant
Waterproof Waterproof 14
Bathrooms Medium Concrete &
compressed
fibre cement
sheet flooring
Water resistant‡
N/A Waterproof¥ N/A 13, 15
Areas adjacent to baths & spas§ (applies to all rooms in
which a bath or spa is installed)
Medium Timber floors
including
particleboard,
plywood &
other materials
Waterproof
N/A Waterproof¥ N/A 13, 15
Concrete &
compressed
fibre cement
sheet flooring
Water resistant‡
Water
resistant§
Waterproof¥ Horizontal
surface
Waterproof*
Vertical surface
Water resistant
Timber floors
including
particleboard,
plywood &
other materials
Waterproof
Water
resistant§
Waterproof¥ Horizontal
surface
Waterproof*
Vertical surface
Water resistant
15
Walls adjoining other vessels
(e.g., sink, basin or laundry tubs)
Low N/A Water
resistant
Waterproof¥ Horizontal surface Waterproof*
Vertical surface
Water resistant
Laundries & WCs Low Water resistant‡ N/A Water resistant¥ N/A
Bathrooms & laundries requiring a floor waste in accordance with Volume One of the BCA High Waterproofed
and drained
N/A Waterproof¥ Waterproof where
through the floor,
otherwise N/A

Australian Standards cont.

Figure 14

Table 7 – General Requirements for Extent of Application AS 3740-2004

Vessels or area where the
fixture is installed
Design and installation criteria
Floors & horizontal
surfaces
Walls Wall junctions
& joints
Penetrations Figure No.
  • Shower area Enclosed & hobbed
Waterproof entireenclosed showerarea, including hob

Waterproof to150mm min. abovethe shower floor substrate or 25mm min. above the maximum retained water level and the remainder to be water resistant to a height of 1800mm min. from finished floor level

Waterproof internal & external corners & horizontal joints within a minimum height of 1800mm above the floor level with a minimum width of 40mm either side of junction Seal all penetrations 14
Enclosed & hobbed Waterproof entireenclosed showerarea includingwater stop Waterproof to150mm min. abovethe shower floorsubstrate and the remainder to be water resistant to a height of 1800mm min. from finished floor level
Enclosed & stepped down Waterproof entireenclosed showerarea includingthe stepdown Waterproof to150mm min. abovethe shower floor substrate or 25mm min.above the maximum retained water level and the remainder to be water resistant to a height of 1800mm min. from finished floor level
Enclosed & preformedshower base N/A Water resistant to aheight of 1800mmmin. from finishedfloor level Seal allpenetrations 14
Insert baths N/A for floor underthe bathWaterproof entireshelf area, incorporating a waterstop under the bath lip and project a minimum of 5mm above the tile surface N/A for wallunder the bathWaterproof to150mm above the lip of the bath* N/A for wall underthe bath* Seal all tap & spoutpenetrations wherethey occur in ahorizontal surface 13
Walls adjoining other vessels(e.g., sink, basin or laundry tub) N/A Water resistant toa height of 150mmmin. above vesselif the vessel is within 75mm min. of the wall Where the vesel isfixed to a wall, sealedges for extentof vessel Seal all tap andspout penetrationswhere they occurin a horizontal surface
Laundries & WCs Water resistant toentire floor Seal all wall to floorjunctions with askirting or flashingto 25mm min. above the finished floor level, sealed to the floor Waterproof all wallto floor junctions,where a flashing isused the horizontal leg shall be a minimum of 40mm N/A
Bathrooms & laundriesrequiring a floor waste inaccordance withVolume One of the BCA Waterproof & drainentire floor N/A Seal all wall to floorjunctions with askirting or flashingto 25mm min. above the finished floor level, sealed to the floor Waterproof wherethrough the floor,otherwise N/A

LEGEND: N/A – Not Applicable / * If a shower is included in a bath, refer to the requirements for shower area walls & penetrations ¥ Does not apply to joinery fittings such as vanities.

Figure 15

Table 7 – Continued

Vessels or area where the     fixture is installed Design and installation criteria
Floors & horizontal     surfaces Walls Wall junctions     & joints Penetrations Figure No.
Unenclosed Waterproof entire     shower area Waterproof to       150mm min. above       the shower floor       substrate or 25mm       min. above the       maximum retained       water level and the       remainder to be       water resistant to a       height of 1800mm       min. from finished     floor leve Waterproof internal       and external corners       and horizontal joints       to a minimum height       of 1800mm above       the floor level with       a minimum width       of 40mm either side     of junction Seal all     penetrations 13
Areas outside the shower       area for concrete and       compressed fibre cement     sheet flooring Water resistant to     entire floor N/A Waterproof all wall       to floor junctions,       where a flashing is       used the horizontal     leg shall be a minimum of of 40mm N/A 13
Areas outside the shower area       for timber floors including       particleboard, plywood and     other flooring materials Waterproof     entire floor N/A Waterproof all wall       to floor junctions,       where a flashing is       used the horizontal       leg shall be a     minimum of 40mm N/A
Areas adjacent to baths and       spa*¥ for concrete and       compressed fibre cement     sheet flooring Water resistant to     entire floor Water resistant to a       height of 150mm       min. above vessel       and exposed       surfaces below       vessel lip to floor     level* Seal edges for       extent of vessel       and junction of bath       enclosure with floor.       Where the lip of the       bath is supported       by a horizontal       surface this area       shall be waterproof       for showers over bath       and water resist for     all other cases Seal all tap and       spout penetrations       where they occur       in a horizontal     surface
Areas adjacent to baths and       spas*¥ for timber floors including       particleboard, plywood and     other flooring materials Waterproof     entire floor Water resistant to a       height of 150mm min.       above vessel and       exposed surfaces       below vessel lip to     floor level* Seal edges for       extent of vessel       and junction of bath       enclosure with floor.       Where the lip of the       bath is supported by       a horizontal surface       this area shall be       waterproof for       showers over bath       and water resist for     all other cases Seal all tap and       spout penetrations       where they occur in a horizontal     surface

BGC Plasterboard wishes to acknowledge and recommend treatment and installation of wet areas as per the Australian Standards

 External Alfresco Ceilings

The construction of external entertainment areas attached to Fasteners a dwelling with a lined ceiling in Australia is proving popular. These areas are inherently exposed to much more arduous conditions to that of the rest of the house internally.

Areas that could be included are areas outside the main enclosed living area of a house or similar environment. E.g. carports, garage ceilings, alfresco areas or similar.

Environment

The environments of external ceilings are often severe and can be effected by;-

  • The generally constant high humidity
  • The climate of the region
  • Wind loads
  • Garage Roller Door Vibration
  • Insufficient perimeter support

To overcome potential problems in these areas it is important to consider the following points;-

  • The correct choice and installation of lining materials, fasteners, jointing and coating materials, designed to suit the environments
  • Correct placement and installation of battens and installation methods
  • The design and detail of the structural components and their protection from moisture
  • Final paint decoration

Condensation

  • Surface condensation and wind loads can be the main causes of lining board and jointing system failure. Insufficient protection can lead to the plasterboard distorting as well as potential mould attack.
  • Use sarking or foil backed insulation underneath metal roofing as this is more susceptible to condensation build up than roofing tiles.
  • It is important that ceiling cavity areas are well ventilated to prevent condensation build up, the Installation of eave and gable vents, roof ventilators etc can assist in this.
  • Building materials and systems may be adversely affected by these severe environmental and physical conditions, which if not installed correctly can lead to ceiling failure and or collapse.

Recommended BGC Plasterboard Materials

  • 10mm Water Resistant Plasterboard
  • 13mm Water Resistant Plasterboard
  • 13mm Wet Area Fireboard
  • 16mm Wet Area Fireboard
  • 10mm Moisture Resistant Flameboard

Fasteners

Fasteners used can be screws or nails and must be to Class 3. When fixing BGC Plasterboard to an external ceiling, use fasteners in the 1/3 spacing method using appropriate fasteners & stud adhesive.

Recommended fixing & spacing

Screw fixings:
Plasterboard width # of Screws Position of screws.
1200mm 5 evenly spaced 1 per recess & equally spaced 300mm centres.
1350mm 7 evenly spaced 1 per recess & equally spaced 225mm centres.

Nail fixings:

Plasterboard width # of nails Position of nails.
1200mm 7 evenly spaced 1 per recess & equally spaced 200mm centres.
1350mm 9 evenly spaced 1 per recess & equally spaced 170mm centres.
Installation

All perimeters to have appropriate framing/noggings etc in order to support all sheet edges. Perimeters to be screw fixed only at 300mm centres. The perimeter may be fixed out with timber noggings or metal plasterers angle (Rondo P18) or equivalent. Framing centres to be at a maximum of 450mm.

All flush joints must be back blocked in accordance with AS/NZS2589:2007.

Paper tape must be used in conjunction with setting type base products in the recessed joins. Base and topping to comply with ASTM C475.

Plasterboard sheets to have a minimum 6mm space from perimeter walls. Fascia boards/perimeter beams should continue at least 20mm below the bottom of the plasterboard ceiling or the perimeter wall/ceiling trim.

Painting

Roll or brush on high quality sealer undercoat designed for external application. Use only manufacturer’s recommended external paint for this application.

Level 4 shall be the minimum level finish for plasterboard.
Level 5 is recommended when critical lighting conditions apply.

Considerations

Before lining the building it is prudent to consider the following design and construction issues;-

  • Consideration must be given to the framing, this may vary throughout Australia especially in high wind and coastal areas
  • It is highly recommended to batten out the ceiling with Rondo 16mm metal battens or 16mm Furring Channel or 28mm Furring Channel or equivalent. These are to be fixed on the appropriate direct fix clips.
  • High-pressure differentials across a wall, may cause the wall to bend and move; hence
  • Ensure that wall and ceiling areas do not exceed maximum allowable areas, heights or lengths, and provide movement and or relief control joints where necessary.

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