No matter how diligent architects and engineers are when specifying sound control measures in buildings, unless contractors follow basic rules when detailing and finishing, sound performance will be downgraded, and putting this right later can be difficult, and very costly. Jason Hird highlights some of the common problems found on site, and demonstrates that effective sound control demands good practices on site.

Acoustic wall and partition systems are designed and tested to provide a set level of sound insulation, generally from around Rw 36 dB for a simple partition, up to around Rw 80 dB for specialist twin frame acoustic wall systems, and these systems work in conjunction with MEP systems and building services to provide essential levels of privacy between two adjacent spaces.

Problems can arise, however, if partition installers take short-cuts, particularly where the plasterboard lining is incorrectly fixed or finished; where attention is not paid to ensuring that any penetrations are correctly detailed or where perimeters are not fully sealed.

Damaged or removed paper liner

The paper liner is an essential component of any plasterboard. It adds additional performance, protects the gypsum core and provides up to 80% of the board’s strength. Removing or damaging the liner will lead to early degradation of the core, compromising not only the acoustic performance, but also the fire performance and robustness of the structure.

Some contractors adopt the practice of removing a 1” strip of liner along the 1,200 mm square profile edge of the board to achieve a flatter finish when taping and jointing horizontal board joints. This is bad practice, and can be overcome by increasing feathering on horizontal joints. In critical lighting areas, it is generally better to flush-fill and tape joints and finish with a 2 mm skim of finishing plaster for a perfectly flat surface.

Over-tightening of drywall fixing screws can also lead to tearing of the liner and cracking of the gypsum core immediately around the screw head. This causes the board around the fixing to become brittle, putting the integrity of the fixing in doubt – a particular problem on ceilings where screws carry the full weight of the lining. The problem is easily overcome by ensuring the correct screw length for the depth of lining and adjusting the screw gun to the correct depth of fixing for the supporting framework.

Penetrations to the plasterboard lining

For effective sound and fire insulation, the integrity of the plasterboard lining must be maintained across the complete structure. Electrical socket boxes, light switches, access panels or other penetrations of the lining must, therefore, be correctly detailed to maintain the same level of fire and acoustic performance as the original lining, though this is not always the case.

In the case of socket boxes, for instance, cut-outs must be neatly prepared to minimise gaps and a plasterboard backing, equal to that of the original lining, installed as a pattress behind each box. The installation should, then, be acoustically sealed with a suitable sealant.

Similar attention must also be paid where access panels are incorporated, to ensure they fully maintain the performance of the surrounding structure.

Poor detailing on metal stud framework

The metal stud framework has been developed to work with the other wall components to provide a precise level of performance to the overall structure. Poor or incorrect detailing can lead to system failure, or cracking of linings that will downgrade the acoustic performance.

Typical problems include taking short cuts at door openings, where some contractors fail to provide correct detailing at the junction of the floor track and door frame. To provide integrity to the frame, the floor track should be snipped and bent upwards to cloak the vertical stud. In heavy and severe duty doors this cloaking must extend at least 300mm up the vertical stud frame to provide adequate reinforcement to the junction.

Similar problems are found where studs need to be extended and incorrect splicing details are used. To maintain integrity, studs should be overlapped by a minimum of 600mm and fixed using two wafer head drywall screws to each flange. Typical bad practice examples include where studs are simply butted together and sleeved with a short length of standard channel, or where an attempt has been made to wrap one section of ‘C’ stud around the back of another.

Alterations to the metal stud framework

Care must be taken when making changes to the metal stud framework, as this can increase the connection between the leaves and downgrade acoustic performance. In the Middle East, it is fairly common practice for contractors to install additional horizontal noggins in the framework to provide additional support for heavy linings or to provide additional fixings points. This will change the dynamics of the framework and impact acoustic performance.

Incorrectly fitted ceilings

Direct fix ceilings, are regularly specified for lining concrete soffits or upgrading the fire and acoustic performance of existing timber joist ceilings. Whilst simple to fit, it is essential that the supporting ceiling track is securely fixed to the soffit using the specially designed brackets. Brackets are first fixed to the ceiling and then screwed securely into both sides of the track before bending back flush with the track.

It has become common practice to short-cut this by bending and fixing only one side of the bracket. This compromises the security of the structure, enabling movement which can cause cracking around the perimeter and downgrading of acoustic performance, and even possible ceiling collapse.

Another common problem occurs on MF suspended ceiling systems where boards are fixed in the wrong direction. Boards must always be located at right angles to the main supporting MF5 ceiling sections – fixing in the direction of the supporting section will increase the risk of the lining quilting or sagging, thus compromising the integrity and performance of the ceiling.

Inadequate acoustic sealing

Finally, the structure must be completely sealed around the whole perimeter to prevent gaps that could provide a path for sound. It is always recommended that lining boards are lifted and fitted flush with the ceiling, and any gap at the base bulk filled with a suitable filler. The perimeter of the wall or ceiling should then be completely sealed with an acoustic filler, to ensure that it is completely airtight.

Cutting corners will inevitably lead to acoustic failure of the structure and expensive remedial work – often at the contractors’ expense.

The writer is Senior Technical Development Manager for dry wall specialist, Gyproc Middle East and member of the Middle East Acoustic Society (MEAS). He can be contacted at jason. hird@saint-gobain.com