Plasterboard can be applied to metal and timber framing or to masonry. Each of the substrates has its own individual fixing specification and compliance with correct fixing procedures is vital to a satisfactory job. Additionally, each of the substrates behaves differently and requires different considerations to enable it to provide a stable substrate.

Timber is most affected by moisture, whilst metal is affected by temperature. In all substrates, dimensional accuracy is the key to success. Plasterboard will follow the plane of the substrate to which it is fixed. Valleys or hollows may generally be easy to hide, but high points are very difficult to conceal.

Plasterboard will not straighten walls or ceilings. No amount of joint compound can make a poorly framed job acceptable.

TIMBER FRAMING

Timber is the original framing material and may be in the form of plantation softwood, hardwood or finger jointed timber. Generally, plantation softwoods and finger jointed hardwood framing is kiln dried to achieve a stable moisture content. Hardwood framing may be partially green and subject to substantial drying shrinkage.

Plasterboard lining, to be defect free, requires a relatively stable substrate and therefore careful maintenance of moisture content is as vital as dimensional accuracy.

CEILING FRAMING

Changes in direction of roof trusses, girder trusses, etc. are now common construction practice. Fixing of plasterboard to some roof truss configurations is almost impossible if manufacturers specifications are to be met.

Result

The end result can mean more ceiling joints, board sagging and a general deterioration in the overall appearance of the ceiling. The introduction of trussed rafters has meant a significant increase in the amount of ceiling problems. Frequently, these complaints reflect on the plasterer and not on the construction in general.

Recommendation

If the design of the ceiling is such as framing members must change direction then it must be recommended that these ceilings be battened. At the very least, noggins should be added to the framing to provide adequate fixing and support.

LARGE CEILING AREAS

In open plan designs in which large ceilings flow into passageways or where the ceiling flows from room to room, the plasterboard will be subject to differential movement.

Result

The joints at the junction of two separate ceiling areas will invariably crack. It is frequently pointless to simply repair the crack - as this kind of failure normally recurs as the ceiling framework responds to normal building movement.

Recommendation

Either introduce a bulkhead (hamper) or door head, or alternatively control joints, to cater for the unavoidable movement and continuous cracking that will occur in these areas.

WALL FRAMING

All studs, plates and noggins must be in alignment. Metal bracing if used must be checked into the framing to achieve the same alignment as the framing.

Result

Failure to achieve alignment will result in valleys and high points in the finished wall sheeting, with subsequent misalignment of skirtings and cornice when fixed later.

Irrespective of the condition of timbers when delivered to site, it is important that when the plasterboard lining is applied, the moisture content of the timber is below 16% (Mandatory in New Zealand).

The practice, common in some parts of Australia to apply plaster-board immediately following framing, but before external brick-work is erected, is not acceptable as the framing may have absorbed moisture during construction as a result of ambient humidity and/or inadequate weather protection.