LUDOX^® FM is an alkaline, aqueous colloidal silica containing 15% amorphous silica with a particle size of 5 nm. LUDOX^® FM has the smallest particle size of all LUDOX^® colloidal silica grades. Because of this it is a very powerful binder of metals, ceramics, and other refractory materials used for high temperature applications. LUDOX^® FM is an excellent densifier for concrete. The small particle size of the amorphous silica in LUDOX^® FM allow it to easily penetrate porous concrete to react with calcium hydroxide in the cement. This forms calcium silica hydrates and increases concrete density and hardness.