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January 12 - January 16, 2015

I’ve heard about using crystalline admixture or crystalline materials on top of concrete to fill voids and make the substrate less permeable. When is this desirable, and what is the best way to use these materials?

Selected Answers

From Mark Puckett of Orfanos Contractors, Inc. on February 2, 2015:
I have seen specs for MMA sealants on bridge decks with filler materials like sand, to fill in cracks and prevent chloride ion migration.

From Joe Miller of NextGen Green Building Products, Inc. dba on January 29, 2015:
Some comments: 1. Crack-bridging is not the same as crack- filling. Crack-filling occurs for existing cracks, many times micro-cracks. 2. Crystalline penetrating liquids are not the same as cement-based crystalline products applied to the surface. Crystalline penetrating liquids need not be abrasion- resistant since they penetrate into the concrete unlike film- forming, cement-based crystalline compounds. 3. Liquid crystalline formulations can fill cracks due to the development of crystals within the cracks. Usually, two types of crystals are formed and can be reactivated by water or water vapor. 4. Coatings, mastics, sheet goods or liquid membranes can be applied to concrete that has been treated with an application of the liquid penetrating crystalline formulations.

From Andrew Piedl of James R. Gainfort, AIA Consulting Architcts on January 27, 2015:
The question uses the term “permeable,” which typically refers to water vapor, not liquid water. The “crystalline” waterproofing products that I am familiar with typically are used to stop water, but these manufacturers will also tout their products' vapor permeability. A common application for these types of products are existing elevator pits with occasional leaking. The waterproofing is applied on the inside, so it is a "negative side" waterproofing. The permeability allows the concrete to dry inward. There are systems that use crystalline products as a base coat (or additive) with a second, flexible coat applied on top. I think that if you are trying to make a slab less permeable, you would use something other than crystalline waterproofing.

From Warren Brand of Chicago Corrosion Group on January 26, 2015:
I am not convinced, but I would like to be. Does anyone have any specific case studies where these materials have been a benefit? Or specific examples of when they would be used and where they would add value over a traditional paint or coating system?

From Chuck Pease of MMI Tank on January 23, 2015:
One would have to determine the service environment of the slab and its intended use. I am not sure from the way you posed your question if you are talking about waterproofing or densifying/hardening of the slab. Chemical densifiers/hardeners have been used in industrial applications for almost 100 years. They have evolved like most other things in our culture from products that were difficult to use and labor-intensive to products that are relatively easy to use. Although they have been used extensively and are believed to improve the performance of the concrete, the mechanisms by which they improve the performance of the concrete are not completely understood. Part of the problem is the complexity of concrete. It is generally understood that every concrete slab is different, and therefore, performance of these types of products will vary from slab to slab. A chemical hardener that works well on a tight, dense slab may not work well on an open, porous slab, and vice versa. Chemical hardeners are believed to work through three different mechanisms. First, we know they react with calcium hydroxide, which is a soft, water-soluble material that is produced during the hydration of the cement. When calcium hydroxide reacts with silica, it is converted into calcium silicate hydrate. This new compound is hard and is not water-soluble. Only 20 percent of the cement is converted into calcium hydroxide, so it is not believed that this reaction fully explains the increase in performance characteristic of the concrete. Second, it is believed that some of the chemical hardeners swell and block the pores or capillaries of the concrete. Third, others deposit an insoluble solid in the pores of the concrete. There are a variety of different types of chemical hardeners — magnesium fluorosilicate, sodium silicate, sodium siliconate, potassium silicates, lithium silicate and amorphous silica. There are variations in the metallic salts, and there are also differences in the silica ratios, as well. Some of the chemical hardeners are acidic and others are alkaline. Some must be scrubbed into the floor, while some can be sprayed on and left. Some are large and some are small. All of these materials have one thing in common — they are using silica, silicate or a siliconate to react with the calcium hydroxide. The metallic salts sodium, lithium and potassium, are just a vehicle to get the silica to the receptor. Chemical hardeners work on the surface of the concrete. They improve the wear surface of the concrete. It is important to keep as much of the material on or near the surface as possible so it can have the greatest impact. Conversely, if we can fill the area below the surface and not become diffused in the concrete, we can have a greater impact on densifying the slab. Siliconates are the largest of the silicas that are used for hardening concrete. Silicas and some of the silicates are some of the smallest. A higher percentage of solids in solution or suspension will have a tendency not to penetrate as well into a dense slab. On the other hand, a higher percentage of solids will work better to plug an open and porous slab. The inverse of this is also true: a lower percentage of solids with a smaller particle size will do a better job on more dense concrete. There are a number of other factors that can affect the depth of penetration into the slab including temperature, moisture content of the air and also of the slab, mechanical force used during application,  rate of application, and dwell time.

From Joe Miller of NextGen Green Building Products, Inc. dba on January 23, 2015:
Just a reminder, in case anyone has forgotten it: Concrete is a porous material that undergoes chemical changes over time as carbon dioxide permeates through it, resulting in hardening and shrinking. There are few coatings I am aware of that can accommodate such shrinkage and be able to remain intact under these tensile loads. So applying clear, liquid crystalline waterproofing compounds seems logical to me since the hydrophilic and hygroscopic actions remain to fill cracks upon exposure to moisture and moisture vapor. They are not static compounds. They get reactivated once moisture becomes present. These are unique actions that traditional water repellents such as silanes and siloxanes simply do not possess.

From Joe Miller of NextGen Green Building Products, Inc. dba on January 22, 2015:
Crack-filling and penetration into capillaries are the principal mechanisms for performance of crystalline penetrating liquids applied to concrete surface prior to applying protective coatings or linings, as I understand the wording of the patents issued by U.S.Patent Office.  Unless the U.S.Patent Office has made a blunder (doubtful), the efficacy of these formulations has been established.

From Lloyd Prontaut of Carolina Management Team on January 20, 2015:
I have seen these materials used a few times in the water industry, but I have seen no value in using them with or instead of coatings. The crystalline materials are less permeable and do a good job of stopping water. However, they can be difficult to properly moisture cure. They don't offer the abrasion resistance that coatings provide, which is evident when it comes time to clean these materials. They have no crack-bridging capabilities, and every project I've seen showed micro-cracking above the water line. In my opinion, stick with protective coatings!

From Warren Brand of Chicago Corrosion Group on January 13, 2015:
I was involved in a very large and contentious project where an architect had specified these materials for an aquarium project. The concrete was going to be overcoated with a high quality coating, and I could find no technical justification for their use. Their crack-bridging capabilities, from what I understand, are almost zero. I have yet to find a project that would benefit from the use of these materials. I'm eager to hear of some.

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Tagged categories: Asia Pacific; Concrete defects; EMEA (Europe, Middle East and Africa); Fillers & surfacers; Latin America; North America; Surface preparation; Surface Preparation

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