Canvas fabric is durable and has a number of outdoor uses. However, using canvas outdoors means it is more likely to develop mould and mildew problems than most indoor fabrics. There are several manufactured products that effectively clean mildew out of canvas, but safety precautions are necessary when using them. If you prefer natural cleaners or want to save money on cleaning supplies, you can thoroughly remove mildew from canvas with consumable items found in most kitchens.
Pour 237 ml (8 fl oz) water, 10 g (2 tsp) of salt and 10 ml (2 tsp) of lemon juice into the spray bottle and tighten the nozzle. Shake the bottle gently until the salt is dissolved.
Spray the cleaner onto the canvas until it is visibly saturated. Wait five minutes, then scrub the mildewed area with the brush. Rinse the cleaner off with clear water.
Inspect the canvas to see if the mildew stain was removed by the first cleaning. If the stain is still there, mix the other 10 ml (2 tsp) of lemon juice and salt in the bowl to make a paste. Apply the paste with the brush and scrub the paste into the canvas fibres until the stain is gone.
Rinse the paste off of the canvas with clear water and let the canvas air dry in a sunny, well-ventilated area.
Borax can be substituted for the salt in the cleaner recipe or can be used with water and a scrub brush to remove mildew stains.