Curing and Sealing
Curing involves maintaining a satisfactory amount of water in the concrete mix while it dries.
Typically, concrete mixes have more than enough water at first. However, that water evaporates quickly unless you take proper measures. The process by which concrete hardens is hydration. As long as hydration continues, the cement paste hardens and becomes denser. Curing protects that process. If concrete cures properly, it will be less porous, making it more difficult for water and salts to penetrate. Curing increases concrete's resistance to impacts, weather and heavy use.
Curing can be as simple as keeping the concrete moist and cool. Concrete that dries in a relatively arid climate ends up weaker than in a cool, moist climate.
Probably the best method for curing concrete is Moist Curing. To moist cure, wet the surface continuously with water for the first week after placement.
Another way to cure new concrete is by using a curing compound. Membrane Curing compounds seal the new concrete with a thin membrane that keeps moisture from evaporating.
Timing is most important when using a curing compound. These products must be applied as soon as final finishing is complete. Otherwise, they could mar the concrete's surface. Also, be sure to check with your ready-mix concrete supplier for recommendations on what to do when it may freeze outside.
Not all curing compounds are the same, especial regarding the ease of removal. Be sure to follow the manufacturer's recommendations completely.
Curing With Sealing In Mind
Just as you paint your home regularly, you should seal your concrete routinely to protect it from moisture and prolong its life. Once hydration is complete, there should be no water left in the finished product. Sealers keep water from undermining the integrity of the mix. Moist curing easily lends itself to sealing because there is no chemical removal involved. However, when using a curing compound, you should use a membrane cure that you may easily remove so that the sealer can penetrate quickly and thoroughly.
By making the sealing choice before your install your concrete, you can inform your contractor of the curing method you prefer. There are two main types of concrete sealers: Those forming a film on the surface of your concrete, giving it a wet look, and those designed to penetrate the concrete, leaving it looking dry, yet water repellent. Each has advantages and disadvantages.
Concrete Film Formers -- The "Wet Look"
Film formers are acrylic or rubber-based compounds. They dry leaving a shiny, wet-looking surface. They protect against some stains better and are often cheaper than penetrating sealers. Film formers do have some disadvantages: They tend to darken the finished concrete and provide less friction for feet and tires.
Penetrating Sealers -- "The Dry Look"
While penetrating sealers usually are expensive, they should last longer. Most penetrating sealers are derivatives of silicone called silanes or siloxanes designed to penetrate concrete pores. Once there, they react with the alkaline materials and moisture present to form silicone, making concrete water-repellent.
Another reason penetrating sealers are popular is that when applied properly, they do not change the concrete's appearance. The major disadvantage is that there can be no other membrane cure or sealer on the concrete when applying, and the concrete must be at least 28 days old.