Concrete Densification

Concrete densifiers play a crucial role in sealing masonry, concrete, and other Portland cement-based materials, transforming them into a solid mass rather than a porous one. Their penetrating qualities provide deep sealing that remains effective for the concrete's lifespan, resulting in a floor surface that is easy to clean and maintain. The chemical densifiers work by hardening and strengthening the concrete mass, offering protection against deterioration, and creating a floor that can withstand heavy traffic. Instead of eroding, this surface self-polishes over time.

What is a Densifier and Why is it Important?

With the advancement of polished concrete, many new products have emerged to support contractors in the polishing process. Among these, concrete densifiers have proven to be the most significant development in concrete polishing. The market now offers a variety of concrete densifiers, categorized primarily by their chemical composition: sodium silicate, lithium silicate, and potassium silicate. When applied to the floor, these densifiers create a denser surface structure and enhance the longevity of the polish. They achieve this mainly by increasing the floor’s abrasion resistance, minimizing susceptibility to scratches, scuffs, and dusting. Dusting occurs when the concrete surface deteriorates, generating fine dust particles as it wears down. This is a common and detrimental issue for polished concrete, as it erodes the polished surface, leaving the unpolished layer exposed. The main purpose of using a chemical densifier on polished concrete is to prevent this deterioration.

So How Do Densifiers Work?

All densifiers operate similarly in terms of the chemical reactions that occur, ultimately affecting the surface composition. Each densifier consists of a type of silicate compound, responsible for modifying the surface characteristics of the concrete. Sodium, lithium, and potassium serve as transport agents for the silicate. When a densifier is applied, it interacts with the free calcium carbonate in the concrete, forming a crystalline structure known as calcium silicate within the surface pores. This calcium silicate structure is crucial for enhancing the surface strength. Depending on the type of densifier used, the byproducts can be sodium carbonate, lithium carbonate, or potassium carbonate, none of which negatively affect the surface characteristics. For sodium silicates, the application entails flooding the surface at about 200 sq. ft./gallon, followed by agitation with a broom or low-speed scrubbing machine. After allowing the densifier to react completely, thorough rinsing removes any excess product. This rinsing is vital since leaving excess sodium carbonate can lead to Alkali Silicate Reaction (ASR), negatively impacting concrete. However, if properly applied and rinsed, ASR is not a concern. Conversely, lithium and potassium silicates are applied by spraying onto the surface at a rate of approximately 500 sq. ft./gallon, without the need for rinsing. Although generally more expensive per gallon, when used as directed by manufacturers, they become competitively priced relative to sodium silicates on a square foot basis.

Which is Better?

Lithium and potassium densifiers are significantly easier to apply, which is why most polishing contractors prefer these over sodium silicates. They eliminate the need for rinsing or surface agitation, reducing the workload for the contractor. These types of densifiers claim to penetrate more effectively than sodium silicates and provide a more uniform surface densification. While some lithium and potassium densifiers may enhance a concrete floor's abrasion resistance by 20-80% depending on the manufacturer, the depth of penetration becomes less relevant since the polished surface is less than 1/64th of an inch. If more than this depth is compromised, the concrete surface is no longer considered polished. In contrast, sodium silicate densifiers can vary widely in abrasion resistance, often providing an enhancement of 40-80%. When evaluating polished concrete options, the 5-10% price difference between floors is negligible when considering the benefits of increased abrasion resistance from the pricier densifiers, leading to greater longevity in the concrete surface.