To understand how a concrete densifier works, you need to understand how concrete forms. When concrete is mixed, Calcium Silicate Hydrate, also known as CSH is formed. It is the primary product of cement hydration, and it is what gives concrete most of its strength. When a concrete densifier is applied to concrete, it simply sparks the same chemical reaction using the free lime and calcium in the concrete to form CSH in the pores of the concrete.
Concrete densifiers increase the density of the concrete, therefore increasing the strength. Because silicate sealers are simply used to spark a chemical reaction, they no longer exist once the chemical reaction takes place. All that is left is the CSH formed in the pores.
There are two primary types of silicate sealers that can be used on concrete, lithium silicate sealers like the Armor L3000, and sodium silicate sealers like the Armor S2000. Both types of silicate sealers will spark the same chemical reaction and produce the same CSH structure. Sodium silicate sealers are slower reacting, but very cost effective, while lithium silicate sealers are faster reacting but come at a slightly higher cost. You would typically only require a lithium silicate sealer over a sodium silicate sealer if you were trying to achieve a higher shine, faster during the concrete polishing process.
Concrete densifiers are great to use on interior and exterior unsealed concrete surfaces where an increase in strength and density is desired. Densifiers do not repel water and do not offer any of the same benefits as a water repellent sealer. If you are applying a concrete densifier and also need water repellency benefits, a water repellent sealer like the Armor SX5000 or Armor SX5000 WB should be applied once the silicate has had a chance to fully react.