If your building code has adopted the National Fire Protection Association (NFPA) 211 standard for fireplaces and chimneys, you must use nonwater-soluble refractory cement to lay chimney clay flue liners. Nonwater-soluble refractory mixes are made with calcium aluminate cement, which sets hydraulically and resists high temperatures and acids. All premixed, ready-to-use refractory products are water soluble and are thus not allowed by NFPA 211.