In search of a pool crack sealer I decided to search all the forums and see what the pros use. I have found that Vulkem 116 is the most commonly cited sealer by pool builders. I've used it to fill all the cracks during our big pool renovation project and so far it's holding up really well. It dries in about a week and this slow drying process may be one of the reasons why it's so strong: Vulkem 116 usually hardens. at a rate of 1/16 inch per day at 75°F (24°C) and 50% relative humidity. After 5 hours it forms a film, after 30 hours it becomes tack-free. Curing time increases with increasing temperature and/or humidity. A good rule of thumb is one extra day for every 10°F drop in temperature.