This article seems to cover it .........
Do not allow bird droppings, earth, sand or vegetable matter to remain in contact with your canvas. These
can stain or, in the case of bird droppings, damage the canvas. Brush such areas gently with a soft brush
(such as an old tooth brush), hose with clean water and allow it to dry. Droppings should be treated ASAP
because of their acidity. An old toothbrush is suitable soft to remove stains such as bird droppings which
can damage your canvas.
Keep your canvas clean by regular brushing both inside and out with a soft bristle brush and hose it down
occasionally with cold, clean water. Start at the bottom of the walls and work upwards.
Never apply soaps or detergents. If you have canvas near a sink, try to ensure you do not get these
materials on thecanvas. If you do, dry immediately with a cloth and wash over with clean water as soaps
and detergents can damage the waterproofing.
Also keep substances such as cleaning fluids, insecticides, petrol, oil, vehicle exhaust, solvents, kerosene or
similar materials well away. Even the use of aerosols such as hairspray and deodorant in the vicinity of the
canvas can be harmful to its life and usefulness.
