Sandstone is a beautiful stone material used indoors and out. Sandstone is used as a patio stone, for walking paths or placed around a swimming pool as the deck. It is found in homes as flooring, fireplace facings, accents on room dividers and less frequently, as window ledges.
It has a porous surface that can absorb mould spores, and given enough rain or constant exposure to moisture, these spores will grow, discolouring the sandstone. Many homeowners who use sandstone outdoors in rainy or humid climates seal the stone to keep moss and mould from growing on it.
Dry the area. Use a hair dryer if necessary to dry the spot where the mould is growing as thoroughly as possible. If the mould is growing on sandstone that serves as pool decking, evaluate how to stop the water from accumulating on that surface. It may be that the pool aerators are blowing back spray onto the sandstone or there is a low spot in the sandstone that collects water when it rains or from splashing.
If there are sandstone paving stones that rain from gutters falls on, consider getting downspout extenders to divert the rain away from the sandstone, minimising the chances of mould growing on the sandstone walkway.
Pour the 3 per cent peroxide on the mould and scrub with a soft brush. If the mould is deeply embedded in the sandstone, perform more than one treatment. Let the area dry before treating again. If the mould continues to grow, use 35 per cent peroxide to treat the area.
Seal the sandstone to prevent mould from growing in the future, especially if the area is going to be constantly exposed to moisture. Some moulds are toxic to people and pets and mould will spread to surrounding areas if given a hospitable growing environment.
Hydrogen peroxide is a safe material to use in the house or outdoors. It decomposes quickly when exposed to air and light. The 35 per cent peroxide is available online or at beauty supply stores, where beauticians use it to colour hair. Stone sealers are available in home improvement stores, hardware stores, and online sites that specialise in stone materials. Most sealers are easy to apply, dry quickly, and will render the surface impervious to moisture and mould.
Do not drink hydrogen peroxide and keep the pets away when working with it.