BONDEK II COMPOSITE SLABSFinishing
For many applications, the BONDEK II profiled sheeting provides an attractive appearance to the underside (or soffit) of a composite slab and will provide a satisfactory ceiling. For example, in car parks, under-house storage and garages, industrial floors and the like. Similarly, the Edge Form will form a suitable edging. In such applications, a cleaning of the exposed surfaces may be required (see Table 2 for cleaning preparations).
It would take minimal additional effort to provide an additional finish if required.
Where the BONDEK II soffit is to be the ceiling, then care should be taken during construction to minimise propping marks (refer to Installation - Propping) and to provide a uniform surface at the side laps (refer to Installation - Fastening Side Lap Joints).
Preparation of the BONDEK II soffit and Edge Form may be necessary to provide a clean surface for the following finishes. The cleaning preparations are shown in Table 2.
Where corrosion product cannot be removed with a kerosene rage, then wire brushing may be necessary. Care must be taken not to unnecessarily remove any of the zinc coating. In situations where the zinc coating is removed, then a suitable paint system must be used.
Various painting systems are available which may be used in conjunction with the different zinc coatings to provide a decorative finish and/or to provide an appropriate corrosion protection system.
For painted soffits and edges, the recommendations in the BHP Technical Information Booklet "Painting Zinc-coated or Zincalume Steel Sheet" may be followed. Field (on site) painting systems from this reference are summarised in Table 3 and are suitable to use with the different zinc coatings, however it should be recognised that thicker zinc coatings will offer a superior product performance in aggressive environments.
The performance of a paint system is influenced by the quality of preparation and application. The paint manufacturer’s instructions should be followed explicitly.
For definition of the Exposure Classification refer to Table 4 of Lysaght publication BDII-2, Part A or refer to t a practising structural engineer.
For painted soffits, it may be preferable to cover the gaps of the ribs prior to painting. BONSTRIP snaps into the gaps of the ribs of the BONDEK II sheeting (see Figure 23). BONSTRIP, when painted, also produces an attractive appearance.
It is suggested that the gap at the side lap joint be filled with a continuous bead of silicon sealant prior to painting.
Finishes such as vermiculite plaster can be applied directly to the underside of BONDEK II composite slabs with the open rib providing a positive key. With some products it may be necessary to treat the galvanised steel surface with an appropriate bonding agent prior to their application.
Plaster based finishes can be sprayed on to give a textured surface or trowelled smooth. They can also be coloured to suit interior design requirements.
Where a building is being refurbished and due to a change of occupancy the fire resistance of the BONDEK II composite slabs may need to be increased. This may be achieved by the addition of a suitable fire-protection material to the underside of the slabs.
The addition of such materials to the underside of the slab will increase the fire-resistance of the slab with respect to insulation, integrity and structural adequacy. In the case of fire spray materials the presence of the BONDEK II open ribs will provide a positive key to keep the fire spray in position throughout a fire.
For details regarding the preparation of soffit, application and thickness of materials to be applied for various situations, refer to the manufacturer of the fire protective material.