On the CC LinkedIn group page, Steve Soderberg asked this question and, boy, did he get soe answers! Here are summaries of a few:
• Dr. Osama M. Shawa: I used chemical curing on a slab on grade in a large factory project. I shall never do that again! The chemical placed stains on the slab and prevented treatment afterwards with epoxy paint and polyethylene. On the other hand, blanket curing needs more scrutinized supervision and follow up for the blanket to stay put and cover the whole surface of the slab for the specified curing time.
• Dave Moore: For polished concrete I always recommend blanket cure for 3 days but do not let it dry out! Seal the edges so it won't.
• Jay Barstow: For decorative ... wet cure or dissipative compounds ... blankets leave marks. For coatings ... blankets or dissipative, but if cure is of UV variety, make sure slab isn't dried in too quickly (needs sunlight).
• Scott Ditto: Silicates are not dissipating cures and do not form a membrane on the surface but rather penetrate into the concrete to harden the surface. Dissipating cures use cheap resins to form a membrane on the surface that holds in the moisture assisting in curing the slab. Most of these dissipating cures adhere to ASTM C309 which often dictates the curing compound to be used. Dissipating resin cures breakdown from sunlight and foot traffic eventually leaving an open surface. They must be fully removed before the application of epoxy coatings, tile adhesives, or other penetrating sealers. These products can be a pain to remove, but will come off with citrus based strippers/degreasers and some elbow grease or a floor machine. They often also discolor the surface because of the cheap resins being used, appearing as a light beige or tan.
• John Fauth: Reactive silicates (sodium silicate, potassium silicate, lithium silicate... doesn't matter it's the silicate that's reactive) can be used as hardeners, densifiers and dust proofers. But they are not curing compounds, do not meet ASTM C 309, and do not cure concrete. Good on those who mentioned it earlier. Similarly, other penetrating chemistries, such as silanes and siloxanes (two sides of the same coin) also do not cure concrete.
Dissipating resins are formulated with hydrocarbon resins. They are not "cheap" resins... they have a specific characteristic (they break down due to UV exposure) that is valuable for specific applications (i.e., when you want to cure concrete without leaving a residual resin barrier to subsequent application of penetrating treatments or polymer coatings). UV exposure and moderate abrasion to cause them to dissipate over time (60 to 90 days or so). They do not turn the concrete tan... the resin begins to appear tan/amber from the UV exposure as it dissipates. As the resin dissipates, the color goes with it.
Here's the takeaway... no method is optimal for use in all situations. Choose your curing method based upon the purpose of the concrete, any subsequent treatment/coating/finish it will receive, and the environment in which the work is being done.
• Bryan Broderick: John Fauth has mention that ASTM C 309 does not recognize silicas as a "cure" for concrete. ASTM C 309 is a very old specification (at least 40 years old) that specifically states "a membrane forming compound" and does not reflect the internal curing of silicas since silicas do not form a membrane. Other than the issue of a membrane not being formed silica treatments meet all of the other ASTM 309 specifications. A lot has happened in the industry in the last 40 years. Gladly we are not using equipment and treatments from 1974 when you consider the age of ASTM C 309--back then we used linseed oil as a sealer.
• John Fauth: OK, here's a dose of reality. Film-forming curing compounds do very little/nothing to enhance hydration within a slab. They prevent moisture loss at the surface of a substrate. Use of a proper C 309 curing method is optional if you don't care what the surface looks like, or its strength and durability. That's why silicates do not cure concrete. They do not prevent moisture loss at the substrate surface. If you don't care about the substrate surface, go ahead and "cure" your concrete with silicates. Better yet, save the time and trouble and don't cure it at all.
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