Masonry external walls are becoming a common construction method, in the contemporary house. Frequently, an internal timber/metal framed wall will abutt an external wall on the same alignment. The plasterboard is often shown to be continuous over the two different substrates.

Result

The finished wall will have approximately a 5mm step in it at the junction of the two different substrates, as the use of adhesive fixed plasterboard over masonry will build out the plasterboard by approximately 5mm. Cracking will also tend to occur at the junction due to the differing expansionary movements of the two substrate materials.

Recommendation

Framing should be set out 5mm proud of the masonry wall, and a control joint or cover batten should be introduced to conceal the joint at the change in substrates.

METAL FRAMING

The undernoted recommendations are not intended to be used as a specification but if followed will greatly help in eliminating most of the problems associated with metal framed construction. Metal frames are prone to greater thermal movement than timber.

Installation

Plasterboard fixing instructions are generally similar to timber frame construction. When the house is full steel framed (including trusses) there are a number of critical considerations to ensure a successful result.

Finishing

Paper tape only to be used for jointing when applied to metal framing.

Foil Backed Membrane

Apply foil backed building paper to roof areas and to external walls.

Expansion Joint to be used

• Where areas of passageways adjoin large rooms or at room junctions where no door heads are used.
• Where plasterboard is installed in patios or soffits.

It is recommended that back blocking be used on plasterboard ceilings as it produces the strongest possible joints and dramatically reduces the incidence of joint cracking and distortion.

For a full description of back blocking see fixing and setting.

Ventilation & Condensation

In warmer climates, the problems of heat conductivity must be addressed. In the worst case, a dark coloured steel roof fixed to steel trusses with an unventilated roof space will produce very high temperatures in the members supporting the plasterboard. High thermal movement will produce peaking, popping and joint breakage.

Recommendation

• Select light colours (reflective) for final roof finish.
• Ventilate roof space with soffit vents.
• Consider ridge or gable ventilation.
• Mechanical ventilation may be considered.

MASONRY WALLS

Drywall Masonry Systems - popularly known as "stick ons" are alternatives to solid plastering and provide significant advantages over the use of wet trades. The success of this system relies totally on adherence to manufacturers recommendations.

The following comments should be used as a guide to ensure proper bonding of the board to the wall.

• Remove any bond breaks or release agent from cast concrete faces.

• Provide a ventilation gap top and bottom of approximately 10mm.

• Use temporary fixing or support to hold sheets in position until the adhesive sets.

• The packers used for keeping sheets off the floor are not to be removed until the adhesive is completely dry.

• Minimise the movement of boards when levelling after initial contact. Once contact with the adhesive has been made the boards should not be pulled back.

• Excessive porosity of the background may cause premature dryout of compound and result in bond failure.

• The use of a bonding agent is recommended over some surfaces.

• Ensure boards are stacked flat prior to use.