Published Friday 22nd of November 2013 // Updated Tuesday 9th of May 2017
Topics: concrete densifier
What is a densifier?
A densifier is substance applied to the surface of concrete in order to fill pores and increase surface density. They are chemical solutions designed to improve surface hardness, density and shine. They react with free lime and calcium hydroxide present in the concrete. This solidifies it, making the concrete surface much less permeable and more resistant to stains.
Where is a densifier used?
The most common uses include hard troweled industrial floors, polished concrete (before polishing) and decorative concrete (before being decoratively stained). Densifiers are also used prior to applying a hydrophobic sealer such as the Sloxa-Tek 8500 since they will increase the adhesion and performance of the 8500 product and make the concrete less permeable.
Why is a densifer needed?
Densification is the process of permanently closing pores in the top layer of the slab. Since concrete is extremely porous, it is susceptible to staining and vulnerable to acid attack that may cause surface etching. Surface wear and dusting are natural characteristics of concrete that need to be considered when deciding to seal concrete. Since concrete is weak, densifiers, hardeners, additives, and protectors are used to help resolve these issues
Types of densifiers:
Densifiers are classified into two generations. Magnesium, potassium and sodium silicate are first-generation products and react with the calcium hydroxide in the concrete. The reaction starts immediately but continues slowly, due to the natural closeness of the pH of concrete. This application process is more caustic and labor-intensive.
Second-generation densifiers are lithium silicate-based densifiers with nano-sized technology and waterborne colloidal silica from nano-sized particles. The suspension of the silicate particles allows the solution to penetrate much deeper before this reaction takes place.
How densifiers work: Lithi-Tek 4500 works by reacting with lime in concrete. During hydration, approximately 20 percent of a concrete mixtures Portland cement is converted to lime, which has no structural value in concrete. However,Lithi-Tek 4500 reacts with the lime to form calcium silicate hydrate (CSH) crystals, the same type of mineral compound that acts as the binder in concrete and imparts strength. Additional CSH fills the pores in concrete and increases the hardness and stain resistance of the surface
Concrete pores are pathways created by migrating water and Lithi-Tek 4500 penetrates the slabs pore structure. Lithi-Tek 4500 is spray-applied and the concrete slab will be dry to walk or drive on in about 6 hours. Over time, ordinary foot traffic will burnish the hardened slab to a soft sheen. Lithi-Tek 4500 also helps resist wear and control dusting.
Why densify before polishing concrete?
Concrete must be between 5000 psi and 6000 psi strong to be polished without a densifier. Concrete that is weaker will not take a polish as well because very small particles of aggregate will pull out of the concrete matrix rather than being held firm to the surface during polishing. By first sealing with Lithi-Tek 4500, concrete is hardened over 5000 psi and you can easily polish concrete leaving the surface with a high sheen. Lithi-Tek 4500 will react with the ingredients in cement to densify while allowing deep penetration to chemically harden and fortify the substrate. After the chemical reaction occurs, the substrate will be more abrasion resistant and help protect the surface from wear, moisture and efflorescence while remaining breathable.