Frequently Asked Questions

1. What is the default ‘Level of Finish’ required for plastering applications?
2. What is back-blocking?
3. What substrates can plasterboard be fixed to?
4. What methods of fixing should I use to install plasterboard?
5. What are the maximum steel/timber framing centres for plasterboard?
6. What is the best way to paint plasterboard once it is installed?
7. How do I finish a plasterboard joint once the sheet has been fixed?
8. How often should I install Control Joints?
9. What type of plasterboard do I need to use for a Fire Rating?
10. What type of lining should I use in Wet Areas such as bathrooms and laundries?
11. How can I improve the sound performance of the walls in my home for a home theatre system?
12. What is Glancing Light?

1. What is the default ‘Level of Finish’ required for plastering applications?
In all there are three ‘Levels of Finish’ available. Level 4 is generally the accepted ‘Level of Finish’ for residential and commercial construction applications where flat or low sheen paints are used. Unless otherwise specified, a Level 4 Finish is the default finish for living areas. A Level 3 Finish is suitable in areas that do not require decoration, and a Level 5 Finish shall be used where gloss or semi-gloss paints are used or where critical lighting conditions occur on flat or low sheen paints. All plasterboard installation must adhere to AS/NZS 2589:2007 Gypsum linings – Application and finishing. For more information refer to FWCIANZ Levels of Finish.

2. What is back-blocking?
Back-blocking is the process of reinforcing wall and ceiling joints with cut-to-size pieces of plasterboard adhered across the back of the joint with MastaBlock Back-Blocking Cement or Cornice Cement. Back-blocking helps prevent joint cracking and peaking caused by building movement, especially in large ceiling areas. Back-blocking forms part of the plasterboard lining standard AS/NZS 2589:2007, and manufacturers’ guarantees/warranties may be void if back-blocking has not been carried out. All back-blocking must be completed before commencing jointing. Each Level of Finish has specific back-blocking requirements. For more information refer to Lafarge Plasterboard’s technical literature.

3. What substrates can plasterboard be fixed to?
Plasterboard can be fixed to various substrates that form wall partitions, ceilings, bulkheads or ducting arrangements. Plasterboard is most commonly fixed to steel studs, timber studs or masonry for wall partitions. Plasterboard can be fixed to ceiling framing by either directly fixing to the joists, or by first installing metal furring channel and then fixing the plasterboard to the furring channel. Furring channel is also used to fix plasterboard linings for suspended ceilings or as an alternate method for fixing plasterboard to masonry on walls. All methods of installation can be found in Lafarge Plasterboard’s technical literature.

4. What methods of fixing should I use to install plasterboard?
The Australian Standard AS/NZS 2589:2007 allows three ways to fix plasterboard to steel or timber substrates. The options are Screw fix only, Nail fix only, or a combination of either screw or nail with adhesive. The preferred method is to use screws or nails with adhesive. The Nail fix only method is only suitable for a Level 3 Finish. Please refer to Lafarge Plasterboard’s technical literature or AS/NZS 2589:2007 for correct installation details such as the spacing of fasteners and adhesive for each method and correct screw/nail type and size.

5. What are the maximum steel/timber framing centres for plasterboard?.
Maximum Framing Centres (mm)

Plasterboard type & thickness Walls (mm) Ceilings (mm) For ceiling areas of intermittent high humidity eg. bathrooms and external ceilings
MastaShield 10mm 600 450
MastaShield 13mm 600 600 450
SpanShield 10mm 600 600 450
SoundShield 10mm & 13mm 600 600 450
WaterShield 10mm & 13mm 600 600 450
FireShield 13mm & 16mm 600 600 450
MultiShield 13mm & 16mm 600 600 450
CurveShield 6.5mm* 550 550
SafeShield 10mm 600 600 450
AcoustShield 13mm 600 600

*For CurveShield refer to Lafarge Plasterboard’s Tech Manual for more information on the maximum frame spacing and minimum curve radius. Note: For plasterboard fixed to masonry refer to Lafarge Plasterboard’s Tech Manual.

6. What is the best way to paint plasterboard once it is installed?
When installed in accordance with Lafarge Plasterboard installation guidelines, the finished surface of all Lafarge plasterboards accept most types of decorative finish: emulsion or oil based paints, stipples, enamels, textured coatings and wall papers. Matt finishes give the best appearance; gloss or sheen finishes tend to highlight any surface irregularities, as will harsh or glancing light. In order to obtain the best finish to the walls Lafarge Plasterboard recommends the following:

Lay down the nap of any scuffed areas using MastaFinish jointing compounds. Surface should be free of dust and other foreign matter
Ensure that the joint treatment is thoroughly dry before applying the sealer
Always seal over jointed and unjointed areas Use roller application for paint. Overworking of sealant coat on jointed areas may cause paint to lift. Roller application applies uniform texture over the entire surface
Use only the best quality paints and other finishes. Use of sealers or undercoats that are water based is preferred to reduce the possibility of raising the paper linerboard nap
Lightly sand between coats if nap is raised Apply finishes in strict accordance with manufacturers’ instructions.

7. How do I finish a plasterboard joint once the sheet has been fixed?
There are only two types of joints formed when installing plasterboard – recessed edge joints or butt joints. The recessed edge joint is formed along the length of the sheets and the butt joint is formed along the width of the sheet. The finishing method is the same for both types of joints, but the width of compound coverage varies. Lafarge Plasterboard recommends the use of paper tape with a three coat compound application: two base coats (or bedding coats) and a third top finishing coat.

8. How often should I install Control Joints?
Control joints must be installed to relieve stresses imposed by structural movement including those due to excessive changes in temperature and humidity. In long, unbroken partitions of wall or extensive ceiling areas, control joints should be placed not more than 12 metres in either direction, at any change in the substrate material and should be aligned with control joints in the structure. Control joints should also be considered at intersecting doorways, large light fixtures, heating vents and air diffusers.

9. What type of plasterboard do I need to use for a Fire Rating?
Only Fireshield, Multishield, ShaftLiner, GIB X-Block and GIB Toughline can be used in fire rated systems. Please refer to the Lafarge Plasterboard Tech Manual for wall, ceiling, column and beam encasement and ducting systems.

10. What type of lining should I use in Wet Areas such as bathrooms and laundries?
Only approved water resistant linings can be used in ‘Wet Areas’ and these include WaterShield, MultiShield and SafeShield. Refer to the Lafarge Plasterboard Tech Manual for installation instructions.

11. How can I improve the sound performance of the walls in my home for a home theatre system?
To improve the performance of your room, consider the following:

To help reduce sound transmission through a wall – install an improved sound resistant plasterboard and wall system. Refer to the Soundshield Techncial Bulletin.
Ensure no gaps or penetrations remain for sound to leak through in a wall by using a sealant. Doorways dramatically decrease the acoustic performance of the room. Even with the door closed, sound can still either flow under the door or still penetrate through the door if the door is of low acoustic performance. Solid core doors are recommended.
Sound will travel into ceilings and through floors, and be transmitted to other rooms and also areas external to the house.
Including insulation in the wall cavity between the studs will reduce sound transmission between rooms.
Resilient mounts or channels can be installed to reduce the level of sound penetrating through the structure.
Double separated stud walls help to reduce the level of sound penetration through a wall, by helping to de-couple the sound transmission from room to room.
Sound is a 3D pressure wave travelling through the air. It will pass from one room to another by travelling through any part of the structure of the room – walls, ceilings, doors, windows – and any gaps. From these, sound will take the path of least resistance. Therefore, the entire room and surrounding environment play a very important part in achieving the desired results.

Soundshield is a high-density plasterboard useful in resisting the penetration of lower frequency sounds, such as the sound a sub-woofer generates. Combining Soundshield with insulation will help reduce transmission of medium and high frequency sounds, such as people talking and high-pitched sounds. To achieve the best results, combine Soundshield with a Lafarge Plasterboard Acoustic System. Refer to the Soundshield Technical Bulletin.

For high performance and specialist requirements Lafarge Plasterboard recommends consultation with an acoustic engineer during specification.

12. What is Glancing Light?
Glancing Light refers to light being cast along the face of a surface showing minute undulations. As a result of this light being cast, a shadow is produced on the other side of the undulation. This draws attention to surface texture variations such as plasterboard joints and patches, which under more diffused light would not be visible. The best way to overcome the effects of Glancing Light is to consider the following factors which will help to achieve the appearance of flatness:
• Design
• Natural and artificial lighting
• Paint effects and paint sheen
• Texture and porosity
• Level of Finish

For more information of the cause, effect and remedial measures refer to Lafarge Plasterboard technical newsletter ‘OnBoard’
and also the industry publication FWCIANZ Glancing Light.