InterShield, a plasterboard product specially developed by Siniat to resist both mould and water, was successfully installed at two townhouse developments by Masterton Builders.

Mould growth in the internal barriers of party wall systems is a serious problem for builders. It often results in costly delays as builders wait for the boards to dry out, while mould removal also adds to the cost of the project.

Clint Masterton, Masterton Builders’ Director of Building Quality & Innovation, recently put the board to the test on two of their townhouse projects and he was more than pleased with the results.

The projects

Masterton Builders experienced the advantages of Siniat’s InterShield mould and water resistant plasterboard first-hand when the product was used in two Masterton Builders townhouse developments in Caringbah and Miranda, NSW. In both instances, the developments consisted of adjoined duplexes.

Siniat delivered InterShield to the Caringbah site 70 days before roof construction started, and 87 days prior to roof start at the Miranda project. Construction at both sites commenced towards the end of 2019, during the rainy summer season.

The product

InterShield is a 25mm fire resistant plasterboard made with a gypsum core and recycled blue liner paper. It provides superior mould and water resistance and is used as part of Siniat’s InterHome – a separating wall system suitable for adjoining residential dwellings such as duplexes or townhouses. It also provides high acoustic performance.

The problem

Mould growth

Mould is a serious problem on building sites, and it often grows on the internal barriers of party wall systems when these structures are exposed to wet weather conditions before the building is roofed over.

According to Masterton, mould was an issue on most of their townhouse projects; the exception being single storey developments when the roof can be constructed very soon after the party wall has been installed.

There are many factors that have an influence on when roof construction in townhouse and duplex projects can start; in the meantime, the internal sections of party wall systems are usually exposed to the elements from two to six months, and sometimes even longer.

When mould grows on interstitial structures, the board needs to dry out and all signs of mould growth have to clear before the board can be sheeted over. This results in costly delays for the builder. There are also significant treatment costs to remove the mould.

“You simply don’t sheet over mould,” Masterton explained. “The mould can continue to fester behind the sheeting where you can’t see it. It won’t take long to turn into a massive problem in the event of a leak.”

Masterton personally experienced the negative health effects of mould in a home after being hospitalised for a bout of pneumonia that had originally started due to mould growth in a rental property.

“When it comes to mould, the health risk is always my biggest concern,” he said.

The result


Despite heavy rainfall at the time, the InterShield boards delivered to the Caringbah and Miranda sites still showed no signs of mould at roofing stage, or at any point during construction.

This was in sharp contrast to similar plasterboard products without InterShield’s unique mould and water resistance qualities used in two other Masterton townhouse projects only a few kilometres away.

“Despite the jobs being in extremely close proximity to each other, and weather patterns, delivery, construction times and conditions being consistent, there was no evidence of mould on Siniat Intershield, but significant visible mould growth was present on the intertenancy walls at the other sites,” said Masterton.

Masterton also put InterShield to the ultimate test at his house: He erected a test sample in his garden and positioned the test sheet so that one side would have zero sun exposure and the base would constantly be damp.

“I ended the trial after approximately 15 months with the exposed side showing no signs of mould and the rear side only developing mould well after 12 months’ exposure to the elements,” he said.

InterShield test

After 15 months of exposure to the elements in Masterton’s garden, InterShield still showed no signs of mould.

“I believe this product is superior to all other gypsum-based intertenancy products currently on the market,” Masterton concluded.