The 1 Gallon DuraZone Refill can be used on patios. driveways. sidewalks. gravel areas except lawns. It kills all types of weeds and grasses up to 6 months. It also prevents new weeds and grasses from emerging. The effectiveness of this 1 Gallon DuraZone Refill will not get washed away due to rain or watering. 30 minutes after application.