Lithium silicates are the new darling of the chemical hardening and densification industry, and though it is important that new products are discussed, it is more important that they are presented, not only for their stated features, but also for what actual benefits they offer. In Joe Nasvik's article “Lithium Silicate Densifiers” (Concrete Construction, December 2008), not one sentence was written about performance. Check any current lithium manufacturer's product literature and you may be surprised that not one of them utilizes the concrete industry's standard for testing abrasion resistance of a horizontal concrete surface, ASTM C779. Not one! For the article to focus on non-issues, such as the percentage of sodium silicate used to make laundry detergents, does nothing to educate the industry, nor convince us of the author's knowledge of silicates and the enormous variety of species that exist. Even within the lithium niche there are differences.
In the first paragraph, the article states “lithium silicate hardeners are growing in market share.” The whole industry is growing, and in comparison to where lithium was last year, yes they're growing, but to imply, without any credible backing, that they sell more than sodium- and potassium-based densifiers, is purely unsupported opinion. The article also raises the specter of ASR (alkali silica reaction). First, let's not confuse ASR problems on an exterior bridge deck to an interior slab. Lithium as an admixture for bridges is an effective tool in fighting ASR outside. Inside, the topical application of lithium may assist in reducing crazing on the surface, but to have ASR within a concrete slab (exterior or interior), a constant 85% relative humidity must be present 24/7. (See http://irc.nrc-cnrc.gc.ca/pubs/ctus/52_e.html..)
In discussing the “function of the sodium, potassium or lithium part of the silicate function … so it can remain in solution,” the article states, “it can remain in solution until it penetrates and then can react.” There is a reason the original densifiers require a working time of 30 plus minutes—it is necessary to achieve the most complete reaction. In addition, the article says, “you don't have to scrub it in.” The presence of dust in the pores and surface tension between the densifier and the floor, says you do. No vacuum traps every bit of dust.
Success is a factor of both quantity and time. You have to ask the question of whether the application rate is set because it is effective, or as a marketing tool? Our industry has achieved great advancement in chemicals, equipment, and tooling, so I'm not saying that with the proper dwell time, in combination with the correct lithium species and coverage, that lithium can't achieve results up there with the highest-rated sodium, but no manufacturer has it on the market today.
The industry has worked hard to become a legitimate flooring option. With that in mind, it's important to remember that ease doesn't equal performance, and performance doesn't come with the wave of a wand.
Director, Marketing & Sales Support
L&M Construction Chemicals
Thanks for sending us your thoughts about the lithium silicate article. I hope you didn't interpret the article to mean that we are advocating or recommending lithium-based products to readers. We provide a wide range of information about generic products; hopefully accurate information. We have written about sodium silicate densifiers in the past. I appreciate your comments because there are so many claims made in this industry about what densifier products can achieve, making it hard to know what is real and what isn't.
I'll add comments to your bullet points:
- The market for lithium silicate densifiers is increasing. There are more sold now than in preceding years. I did not mean to imply in the article that their sales exceed sodium or potassium densifier sales.
- ASR concerns: Lithium silicate densifiers have some effect on reducing ASR, even for topical spray applications. The pH of the raw material lithium silicate solution is 10.8. The pH of the raw material sodium silicate solution is 11.3. The pH is a negative logarithmic function so the pH increase of 0.5 units corresponds to more than a threefold increase in hydroxide ions (actually 3.162 times) and an increase in pH of 1.0 unit would correspond to a tenfold increase in hydroxide ions. In this regard lithium silicates are less problematic. The use of recycled glass aggregate broadcast on fresh concrete surfaces as a decorative finish is more popular now. Light profile exposed aggregate sand finishes are also—many sands are susceptible to ASR.
- Amount of application: One key to the absorption of all silicates into concrete surfaces depends in part on the addition of a surfactant. Products are different in that regard according to what the formulator does. Also, the reaction between silicates and calcium hydroxide in concrete is a slow reaction that takes place over time. There is some quick benefit but more over time. The most popular use for silicates at present in the concrete market are high-end Big Box floors and diamond polished floors. Floor surfaces tend to be very clean (with vacuum removal systems), though warehouse floors have very impermeable surfaces these days.
- The key to applying all silicate products is to apply the right amount. This is true with spray applications as well. Manufacturers of lithium silicate products do recommend spraying their products. But every product is different. There are different amounts of silicate in everyone's product (more doesn't necessarily mean better) and additives such as surfactants. We hear about excessive applications of lithium silicate products that result in white deposits that can only be removed mechanically. So spray applications work? In the Big Box market, they are used in the diamond polishing process to harden surfaces to higher polishes. Higher reflectance is measured by gloss meters to meet the owner's requirement.
- The use of sodium silicates in laundry detergents represents 38% of the total production of sodium silicates. Some 1.2 million tons of sodium silicate on an anhydrous basis were sold in the U.S. in 2001. See the Oxy and The Innovation Group Web sites to learn more about this. Lithium is a lighter atomic mass element than sodium, so a given amount of lithium silicate will contain more silicate ions than the same amount of sodium silicate. In addition, the lower pH noted above increases the rate of reaction, resulting in a more rapid increase in the surface hardness.
Concrete Construction magazine