SEALER CONCRETE KRYSTAL25 OTC 5gl PAIL. Krystal 25 OTC is a low VOC non-yellowing treatment and cure concrete. It has dual technology which makes its application process much easier and with better results. It is easy to apply even in extreme summer conditions and its Air-Release technology facilitates the release of bubbles or air. In addition, its film is durable and its high solids content makes cleaning much easier.