Clay brick veneer claddings remained popular in the 1970s, and concrete brick veneer was also used.
Veneer construction consisted of an outer skin or veneer of fired clay bricks or concrete brick constructed in front of standard timber framing, but with a cavity separating the two.
The cavity is at least 38 mm (NZS 1900 Chapter 6.1, which was current until 1978, specified a minimum cavity width of 38 mm).
The framing provides the structural component to the wall and the veneer is tied to the timber with metal ties. The cavity prevents moisture from being transmitted from the brick to the timber.
Though 1970s houses are usually weathertight, there may be a risk of moisture getting in through the gap between the top of a brick veneer cladding and a soffit lining. See moisture and weathertightness.
The most common clay bricks were the New Zealand made standard (225 long x 108 wide x 75 mm high) and the roman (300 long x 95 wide x 50 mm high), but other sizes were also manufactured locally. A 38-50 mm cavity and nominal 100 mm wall framing thickness resulted in a typical overall wall thickness of 230-254 mm.
1970s locally-made bricks were available in a range of colours (such as the buff colour of a Huntly brick or the red from Benhar, plus dark, variable dark, dark shades, natural, chocolate, autumn, golden buff) and styles such as:
- plain or smooth face
- clinker, which had coal-like inclusions in the clay
- rumbled, where the edges were artificially rounded after manufacture
- burnt, where the brick was fired at a higher temperature
- antique, which had a dimpled face
- tapestry, which had a vertical ribbing like a brushed finish
- Hoffman (named after the kiln they were fired in), which had a colour variation across the face.
Concrete bricks (called split stone) were a cast unit, typically 397 mm long x 92 mm wide x 92 mm high, with flat surfaces except for the exposed face which was a finish formed by splitting the larger unit apart (into two brick sized units) after manufacture (Figure 1).
Half and three-quarter length and half-height blocks were also manufactured. A limited range of colours was produced, although white was most popular.
Bricks were typically laid in a stretcher bond pattern, but a range of other patterns was used.
The mortar was generally a mix of one part cement to three parts sand, coloured to match or contrast with the bricks. Joints could be formed in a variety of ways and were a maximum 9.5 mm wide.
Ties to secure the brick to the timber framing (Figure 2) were likely to be proprietary galvanised mild steel face-fixed ties that allowed the tie to be fixed over the building paper.
No. 8 standard wire gauge (SWG) galvanised wire that was twisted into a shape so that one end could be embedded in a joint, and the other end secured to the side of a stud, may have still been used early in the period, but this did not allow the use of building paper.
The ties were typically inserted at 900-1200 mm centres horizontally, and in every fourth course vertically, in a staggered formation. Additional ties were inserted at corners and around openings. They were sloped towards the brick face so that any water in the cavity would be drained away from the timber framing.
Kraft building paper was not always shown in detail books or installed, particularly where ties were fixed to the side of the stud.
Ventilation is required in the cavity between the brick veneer and framing so that any moisture is able to dry out.
Typically the concrete foundation wall supported both the brick veneer and timber framing on a wide continuous foundation wall (Figure 3). Weep holes were required in the lowest course of bricks to provide ventilation, and also to allow any water that penetrated the brick veneer to drain out. Weep holes were also required where the foundation was a reinforced concrete floor slab.
Early 1970s detail books with suspended timber floor construction showed the brick veneer cavity open to the subfloor, which allowed moist air to be transported up the cavity into the roof space, often leading to significant moisture problems. During renovation, the wall cavity should be closed off from the subfloor and from the roof space.