Concrete can crack both before and after it hardens. Waterproofing concrete structures is essential to keep moisture out of the facility and to safeguard the structural components of concrete and embedded reinforcing steel. If the concrete's integrity is preserved, it can stay watertight. For example, if a ceiling collapses due to dry rot, the moisture from the body heat of anyone trapped beneath the debris will continue to drain away rather than accumulate as ice or steam, which would otherwise happen if the structure were not waterproof.
The most common method for waterproofing concrete is epoxy coating. This is a two-part resin system that is applied in several thin layers with a trowel. The first part of the resin cures at room temperature, while the second part requires either heat or pressure to complete its formation. Epoxy coatings are durable and flexible, and they resist damage caused by sunlight, salt, acid, alkalis, and other chemicals. They also help prevent corrosion of metal reinforcements within the concrete.
There are different types of epoxies available for waterproofing concrete. Some are semi-permanent while others are permanent. Semi-permanent epoxies can be removed from concrete once the danger of cracking has passed. These types of coatings are useful when repair or replacement of the coated element is necessary. Permanent epoxies remain on the concrete forever and cannot be removed without damaging the surface.
Concrete weighs heavier than water, and when placed into any container or shape, it will displace the water rather than mixing with it. Concrete hardens as a result of a chemical reaction and does not need to "dry" to harden. Water is essential for the chemical interaction with the cementitious material to occur. However, if you want your concrete to dry before adding another layer, pour a thin film of oil over the surface. The oil will prevent any further hydration until it is removed.
If you expose concrete to air instead of a plastic bag, it will naturally cure or harden over time. This is called "air-curing", and it can be an advantage because it prevents moisture from entering the concrete while it cures. Curing concrete this way requires no special treatment other than providing an environment where oxygen can reach the mixture. Concrete that is not air-cured may require additional steps such as heating or spraying with chemicals to accelerate the setting process.
Concrete sets in three stages: initial hardening, final drying, and full strength. Initial hardening occurs within an hour to a day after pouring. The mix design should include sufficient water for proper hydration of the cement particles and formation of a strong bond between them. If there is not enough water, the concrete will appear dull and heavy.
Water is a necessary component in the production of concrete. Water supplies moisture, which gives concrete strength throughout the curing process. While water is one of the most crucial constituents in concrete, it may also be the most harmful in large quantities. Concrete can absorb up to its own weight in water without suffering any adverse effects as long as it is kept out of direct sunlight and has some ventilation to prevent excessive drying out.
If you have concrete that is exposed to excess moisture, it will become acidic. Concrete that is acidified above a certain level will begin to break down, causing it to lose its strength and potentially leading to corrosion of metals such as rebar within the concrete. Corrosion from acidification can also affect other materials such as stone, tile, and asphalt. If this occurs, they need to be repaired or replaced so that your concrete isn't the cause of more damage.
Moisture can also lead to mold growth in areas of the building where there is sufficient humidity and an adequate supply of nutrients. The best way to avoid moisture problems with concrete is through careful monitoring and appropriate maintenance. If you notice any cracks in the surface or see any moisture on the interior side of exterior wall panels, have the concrete inspected by a professional before it gets any worse.
Too much or too little water can have negative effects on the durability of the concrete.
The amount of water required depends on the type of concrete and the environment it will be exposed to. Concrete that is used in areas with high humidity requires more water than dry-climate concrete. The texture of the aggregate in the mix also affects how much water is needed. Coarser aggregates require more water than finer ones. The length of time that the concrete remains wet after mixing is another factor in determining the required water content. If it is not watered down enough, the concrete will appear dull after it has cured instead of shiny like fresh paint. If it is watered down so much that it runs, the surface will be soft instead of hard like stone.
Concrete that is placed in humid climates should be watered down slightly with rain or irrigation water. This allows for sufficient drying before the next watering cycle begins. Damp places are prone to mold growth, so making sure that there is no standing water in areas where concrete is being placed helps prevent problems with fungi and bacteria that can lead to disease.
Keeping the concrete wet aids in the curing process. Concrete hardens as a consequence of a chemical interaction between cement and water known as hydration, not because it dries. The hardening, or curing, process continues as long as there is moisture in the concrete. Moisture can be added to the concrete during mixing or after it has set up for several hours.
Water that contacts concrete before it has cured may react with the alkalis in the cement, causing them to dissolve into the concrete. This is called "solutioning." As these ions are dissolved into the concrete, they become available to act as conductors of electrical charge. This allows more calcium carbonate in the cement paste to be converted into calcium-ion-exchanged hydrate products, which contribute to the concrete's strength over time.
If water is added to wet concrete, some of it will evaporate before the concrete sets up. This is why moist locations like roofs and sidewalks are often cited as being contributing factors to dry-rotted buildings. Dry rot occurs when wood cells decompose without oxygen around them, so they turn to dust which mixes with the concrete.
Concrete that is exposed to direct sunlight can reach temperatures as high as 110 degrees F (43 degrees C). At these temperatures, any water inside the concrete vaporizes quickly, preventing the formation of hydrogen bubbles that would otherwise reduce the strength of the material.