Rendering AAC panels and foam cladding

AAC (autoclaved aerated concrete) panels and EPS (expanded polystyrene) foam boards are lightweight wall claddings that only work once they are finished with a flexible coating system matched to the panel. The panel maker’s installation guide, not habit, decides the primer, base coat, mesh and top coat. A plain cement render or a single coat of paint is the wrong finish for both.

Where these systems turn up around Geelong

AAC panels and foam board are used on second-storey additions over brick ground floors, on rear extensions, on newer homes in growth areas, and on beach houses where a light frame was clad and rendered. Common reasons owners look for a provider:

• A new extension has been framed and clad and needs its coating system applied.
• Joints between panels are showing through the finish as straight lines or cracks.
• The coating has been chipped or punctured near the ground, by mowers, bins or ladders.
• A foam-clad home is being bought or sold and the buyer wants to know what is on the wall.

AAC panels and EPS foam compared

Point	AAC panel (for example Hebel)	EPS foam board
What it is	Steel-reinforced aerated concrete panel	Polystyrene board fixed to the frame
Fire behaviour	Non-combustible, according to CSR’s Hebel guide	Combustible; restricted on some building types in Victoria
Impact resistance	Firm surface	Soft; dents if knocked
Coating	Maker-approved flexible acrylic system	Maker-approved mesh and render system
Typical fault	Joint lines and cracks at panel joints	Punctures, dents and cracking at openings

What CSR’s AAC guide asks for

CSR’s 2016 design and installation guide for Hebel PowerPanelXL external walls on houses and low-rise residential buildings sets out the coating requirements:

• A specific fit-for-purpose coating system must be used. The guide says a simple paint coat would most likely be inadequate.
• It recommends Dulux AcraTex systems, and it does not recommend site-mixed cement render or cement-based premixed renders on PowerPanelXL.
• The coating must be able to bridge a crack of at least 1 mm and should keep water out while letting vapour escape from the panel.
• Any variation to the coating system must be approved and warranted by the coating maker.

The coastal rules matter on the Bellarine

The same guide treats buildings within 1000 metres of a shoreline or a large expanse of salt water as coastal. For those walls it asks for one of these measures: movement joints properly caulked, walls exposed enough for rain to wash them, or walls under eaves washed down twice a year to remove salt. It also calls for Class 4 corrosion-rated fasteners and says panels must be washed with fresh water to remove salt before the coating goes on. Homes near the beach at Ocean Grove and streets close to Corio Bay can sit inside that distance, so measure yours and ask how a provider will handle it.

Victoria’s rule on rendered EPS

The Building and Plumbing Commission’s prohibition page explains that from 1 February 2021 the Minister for Planning prohibited EPS used in a rendered external insulation and finish wall system on Class 2 to 9 buildings required to be of Type A or Type B construction under the Building Code of Australia. The prohibition does not apply to Class 1 and Class 10 buildings, so a detached house is outside it. Units, apartments and other building types may be inside it. If your building is not a stand-alone house, ask a registered building surveyor before anyone quotes foam.

Registration and permits

Fixing new cladding is its own registration class, Domestic Builder (limited to external wall cladding). It is not one of the single trades that can skip registration, according to the BPC page on classes of domestic building work. Once the contract is worth more than ten thousand dollars, the person you sign with must be registered. Any building work that needs a building permit also needs a registered practitioner, whatever its value. For an extension, ask the building surveyor whether a permit applies, and do not rely on anyone telling you a permit is not needed.

Coating panels that someone else has already fixed is closer to a rendering job, but it still has to follow the panel maker’s system.

What the coating work involves

1. Check panel fixings, joints and flashings before any coating starts. Gaps and loose panels have to be fixed first.
2. On a coastal site, wash panels with fresh water and let them dry.
3. Fill and reinforce joints with the products the system specifies.
4. Apply the base coat and bed reinforcing mesh where the system calls for it, lapping it at joints and around openings.
5. Apply the texture or finish coat.
6. Apply the membrane top coat to the specified coverage.
7. Seal junctions with windows, doors and other materials with a compatible sealant.

Costs

The published Geelong cost guide does not list prices for AAC or foam coating systems, so no range is given here. Price depends on panel area, joint repairs, scaffold and the system chosen. Use the per square metre figures for texture coating and the Geelong cost guide as a starting point when comparing written quotes.

A careful provider will not

• Apply site-mixed cement render to AAC panels.
• Skip the fresh water wash on coastal panels.
• Mix brands within one coating system.
• Quote foam on an apartment or other non-house building without checking the prohibition.
• Leave panel joints unreinforced because the job is small.

What to do next

Find any paperwork from the original build, including the panel brand and coating system if it is known, and photograph the joints and any damage. Ask for AAC or foam cladding coating quotes. The site passes enquiries to independent providers, and the provider you hire is the one responsible for the scope and the result. Check their registration class on the BPC practitioner search before you sign.

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