Cotton canvas, used for tarps and tents by campers and the military, provides durability and ruggedness in adverse weather conditions. Cotton canvas has mild waterproof properties but requires waterproofing to withstand drenching rain or heavy snowfall. Traditionally, linseed oil or wax was used to make cotton canvas waterproof. Today, chemical waterproofing sprays have made the job of waterproofing cotton canvas easier.
Hose down the cotton canvas tent or tarp. Scrub the tent with the brush to remove mud and dirt.
Fill a bucket with warm water and add a mild detergent. Mix well and soak the tarps or tent in the water for about half an hour. Air-dry the tarp or tent completely after rinsing with warm water.
Place the dry tarp or tent in a well-ventilated place like a garage. Cover any plastic parts like windows or zippers with foil.
Wear gloves and safety glasses. Hold the spray about 8 inches away from the canvas. Spray the waterproof spray on the canvas. Spray two light coats one vertically and one horizontally on the canvas. Keep spraying till you cover the entire canvas. Make sure that the edges of the tarp or tent are properly waterproofed. The waterproof effect of the spray should last for one year.