Turning potentially poisonous plasterboard waste into gardening treasure

May 28, 2023

Plasterboard – including the trademarked product Gib – are the large sheets used to line walls, typically with white gypsum plaster sandwiched between two layers of heavy-duty paper.

It's what builders and home renovators were going crazy for during last year's post-lockdown building surge.

Look in a skip at the "gibbing" stage of a new build or home renovation, and It's likely to be full of plasterboard. Around 12% of wall boards are estimated to be wasted at the point it is installed, with most offcuts heading straight to landfill.

In the anaerobic, oxygen-deprived conditions of landfills, plasterboard turns toxic. When wet or mixed with biodegradables such as food, plasterboards can produce up to a quarter of its weight of poisonous hydrogen sulphide.

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"In the UK, Europe and North America you are not allowed to put gypsum in landfills because of the dangerous off-gassing," says Mark Roberts, a Senior Waste Planning Specialist at Auckland City Council.

All the gypsum used in New Zealand plasterboard comes from Australia, says Roberts. Sending it to landfill wastes a precious resource we could be making better use of.

Getting a circular system going to recycle and reuse this mineral, means the less we need to import as a country and the less that needs to be mined from the Australian desert.

When scrap plasterboard is processed the gypsum – a common mineral – can be separated from the paper using an extractor. The paper can be recycled, and the gypsum ground into a powder to be used as fertiliser.

"Virgin gypsum is really expensive and this is about a third of the price," says Elaine Morgan, CEO of Green Gorilla. "This is an excellent alternative for farmers and horticulturalists."

Gypsum is used in the agricultural and horticulture industries as a natural soil conditioner and clay buster. Added to soil, it's a low-cost way to give avocado trees and kiwifruit vines extra calcium.

You can also use it in your home garden. As well as calcium, gypsum adds sulfate and can improve soil aeration, the movement of water though the soil, and increase the ability of soil to soak up water, helping reduce runoff.

When planting native seedlings for riparian planting and rewilding, plasterboard offcuts covered with mulch are effective for suppressing kikuyu grass and other weeds that can overwhelm small trees as they grow.

Fletcher Building recommends that only unpainted plasterboard offcuts from new build construction sources should be used in gardens, as old offcuts sourced from renovation or demolition may contain paint and unknown contaminants.

Diverting waste from landfill takes a bit of forward planning, says Roberts. An advisor to the Ara Education Charitable Trust, Roberts is helping Sarah Redmond and team develop their waste plan as they restore the Forever House.

One way to recycle plasterboard waste is to use a dedicated collection bag or skip supplied by your local waste recycler, such as Auckland's Green Gorilla, Hamilton's Purpose Fill or WasteCo in Christchurch.

"We don't supply bags in Christchurch but can supply multiple bins for plasterboard, wood and metal, with another skip for non-divertible waste," says Carl Storm, WasteCo COO. "If a customer has a large enough site for multiple bins this works, but as most sites have a very small footprint, WasteCo can provide one bin for waste and all recyclables for sorting in our 4000m2 purpose-built Christchurch sort facility."

Recyclable plasterboard is processed and used by a local landscape gardening firm as a compost additive.

Hamish McBeath, CE Building Products with Fletcher Building says the company is developing a new state-of-the-art plasterboard plant, in Tauranga. "Starting from the ground up has given Winstone Wallboard a unique opportunity to design new sustainability features into the plant," says McBeath.

"One feature is a plasterboard waste recycling facility which will allow us to use recycled gypsum in the Gib plasterboard we create."

McBeath says starting by recycling their own production waste, long term the company intends exploring they can recover waste plasterboard from the market, recycle it and turn it into new plasterboard.

The Ara Education Charitable Trust (AECT) is an innovative collaboration between industry, government agencies and schools to create work and training opportunities for South Auckland school-leavers. Click here to donate.

Follow the progress of the Forever House for expert advice, tips and tricks on sustainable building. Over the coming months, the AECT, Stuff and our sponsors are turning a derelict house into a warm, dry, eco-friendly and low cost home.