Efficacy of wollastonite-enriched acrylic coatings against fungal decay in non-treated and thermally-modified wood

Wood is a living material that has built human shelters for thousands of years, yet it remains vulnerable to the elements. When left unprotected, it rots from fungi, burns in fire, and warps as moisture levels change. While scientists have long developed chemical treatments to stop this decay, many of these solutions are toxic or difficult to apply. A popular alternative is thermal modification, a process where wood is baked at high temperatures to change its internal chemistry, making it less appetizing to rot-causing organisms. However, even heat-treated wood is not immune to all types of decay, and the industrial machinery required for this process is expensive. This leaves a gap for a simpler, cheaper way to protect wood, particularly for those who want to avoid harsh chemicals. Researchers have turned their attention to a common mineral called wollastonite, a needle-shaped rock often used in plastics and ceramics, to see if it could strengthen protective paints and stop wood from rotting.

A team of scientists from universities across Iran, Europe, and Australia set out to test whether mixing this mineral into a standard acrylic paint could shield wood from fungal decay. They worked with three distinct types of wood: beech, a dense hardwood; poplar, a lighter hardwood; and spruce, a softwood. To simulate real-world conditions, they prepared two sets of each wood type. One set was left in its natural state, while the other was subjected to thermal modification by heating it to 185 degrees Celsius for four hours. This heat treatment alters the wood's chemical structure, removing some of the sugars that fungi feed on. After the heat treatment, the wood samples were conditioned to stabilize them.

The researchers then applied different coatings to these samples. Some pieces were left bare to serve as a control, showing how much the wood would rot without any protection. Others received a standard water-based acrylic paint, a common coating found in many hardware stores. The final group received a special version of that same paint, but with wollastonite mixed in. The mineral was added at a specific ratio, creating a suspension that was thoroughly blended into the paint before application. Each piece of wood received two coats of the paint, applied a day apart, resulting in a dry layer about 210 micrometers thick. Once coated, all the samples were placed in a controlled environment and exposed to two aggressive types of wood-decay fungi for four months. One fungus, known for causing brown rot, attacks the structural fibers of the wood, while the other, a white rot fungus, breaks down the wood's color and strength.

After the four-month exposure period, the results were striking. The untreated wood samples suffered heavy damage, losing significant amounts of their mass as the fungi ate away at the material. In some cases, the unprotected wood lost nearly 40 percent of its weight. The standard acrylic paint offered some help, reducing the mass loss, but it was not a perfect shield. In certain conditions, particularly with the beech wood, the paint film cracked and peeled, allowing the microscopic fungal threads to penetrate the wood underneath. However, the samples coated with the wollastonite-enriched paint performed exceptionally well. The mass loss in these samples was drastically lower, often dropping to less than 3 percent, regardless of whether the wood was heat-treated or not.

The researchers examined the samples under powerful microscopes to understand why the mineral-enhanced paint worked so well. They found that the needle-like shape of the wollastonite particles acted as a physical reinforcement within the paint film, making it tougher and more resistant to cracking. More importantly, the mineral seemed to form strong chemical bonds with the paint itself, creating a cohesive layer that was difficult for fungi to breach. The paint film remained nearly intact even after months of fungal attack, whereas the plain paint had deteriorated significantly. The mineral also appeared to act as a barrier, slowing down the movement of oxygen and water to the wood surface, which are essential for fungal growth. In some instances, the researchers observed that the mineral itself might have interfered with the fungi's ability to grow on the surface, limiting the spread of the mold.

The study also measured how much strength the wood retained after the fungal attack. Wood that had been eaten away by fungi became weak and crumbly, losing much of its ability to bear weight. The samples protected by the wollastonite paint, however, kept their structural integrity. Even the wood that had not been heat-treated but was coated with the mineral paint held up almost as well as the unexposed wood. This suggests that the paint did more than just sit on the surface; it actively prevented the decay process from compromising the wood's internal structure. The combination of thermal modification and the mineral paint provided the best protection, but the paint alone was a powerful defense for untreated wood.

The findings indicate that adding a common, inexpensive mineral to a standard paint can create a highly effective shield against wood rot. This approach offers a practical solution for protecting wood without relying on toxic chemicals or expensive industrial heat-treatment facilities. The researchers concluded that this method is easy to apply and reliable for both hardwoods and softwoods. While the study was conducted in a laboratory setting, the results suggest a promising path forward for preserving wood in real-world applications, offering a way to extend the life of wooden structures while keeping the protection process simple and environmentally friendly.