Ethan Clarke
Concrete is a versatile material used in various construction projects, from patios and porches to iconic structures like the Sky Tower in Auckland. One of the critical aspects of working with concrete is ensuring proper curing, which begins as soon as water is added to the cement, initiating a hydration reaction. During the curing process, concrete must be protected from adverse weather conditions and environmental factors to prevent surface cracks, discolouration, and reduced strength. This is where the question of when to cover concrete with plastic arises. While some sources recommend covering concrete with plastic sheeting to control moisture and prevent discolouration, others caution against it, highlighting the risk of discolouration and the need to maintain a delicate balance in timing. So, when is the right time to cover concrete with plastic, and how long should it stay covered?
| Characteristics | Values |
|---|---|
| Best time to cover concrete with plastic | As soon as the concrete has hardened enough to resist surface damage, typically within a few hours of placement |
| Minimum time to cover concrete with plastic | 7 days |
| Ideal temperature for concrete to cure | 40 Fahrenheit |
| Disadvantages of covering concrete with plastic | Can permanently discolour concrete |
| Alternative to plastic covering | Wet burlap coverings |
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What You'll Learn
Covering concrete with plastic protects it from the elements
Covering concrete with plastic sheeting, also known as "visquene" in the industry, is a common practice to protect it from adverse weather conditions such as rain, snow, or freezing temperatures. It is particularly useful in cold and wet conditions as it helps retain moisture and cure the concrete harder.
Concrete is a mixture of cement and water that undergoes a chemical reaction called hydration, which releases heat and leads to the formation of calcium silicate hydrate (C-S-H) gel. This gel binds the aggregate particles together, giving concrete its strength. However, if the concrete dries out too much, the hydration reaction stops, and the concrete may not reach its full strength.
Applying plastic sheeting to fresh concrete can help prevent the surface from drying out too quickly. It is recommended to cover the concrete for at least 7 days to ensure proper curing, although the duration can vary depending on environmental conditions and the specific concrete mix. One should be cautious, however, as applying plastic too early, when there is still late bleed water on the surface, can lead to problems. Moisture can coagulate with the plastic, creating air pockets in areas where there is no full contact.
Additionally, plastic sheeting can cause discoloration on the concrete where the two surfaces touch. To avoid this, some people suggest using alternative covering methods such as wet burlap or tarps. Others recommend misting the concrete with water during the first day or two after pouring, ensuring constant wet curing rather than intermittent wetting and drying.
Overall, while covering concrete with plastic can be beneficial in certain weather conditions, it is important to be mindful of the timing and potential drawbacks to ensure the desired results.
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When to apply plastic sheeting
Concrete should be covered for at least 7 days to ensure proper curing. However, the duration can vary based on environmental conditions and the specific concrete mix used. It is important to begin the curing process as soon as the concrete has hardened enough to resist surface damage, typically within a few hours of placement. Concrete that dries out too much will stop curing.
Plastic sheeting can be applied to concrete to protect it from cold and/or wet conditions. It helps to keep the heat generated during cement hydration and provides curing protection by preventing the concrete surface from drying out. However, applying plastic too early can cause problems if finishing and late bleed water are still present on the surface. When the plastic makes localized contact with a "still wet" surface, the moisture will coagulate with the contact surfaces of the plastic. If there are areas where the plastic is not in full contact, air pockets will form. Plastic sheeting can also cause permanent discoloration of the concrete.
To avoid discoloration, the plastic sheeting should be removed after a few days and the concrete misted with a hose daily. It is important to ensure that the plastic sheeting lays flat as wrinkles can also cause discoloration.
In summary, plastic sheeting can be applied to concrete within a few hours after placement to protect it from the elements and promote curing. However, it should be removed after a few days to avoid discoloration, and the concrete should be misted with water to maintain moisture.
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Potential consequences of not using plastic sheeting
Concrete is a porous material that absorbs moisture from the air and its surroundings. When concrete is first poured, it needs to be kept moist so it can gain strength and durability during the curing process. Plastic sheeting is often used to preserve and protect newly laid concrete by acting as a protective barrier. This barrier helps to prevent moisture loss, temperature fluctuations, and debris accumulation, ensuring the concrete is strong and durable.
There are several adverse consequences of not using plastic sheeting to cover newly laid concrete. Firstly, without a protective barrier, the concrete is susceptible to rapid moisture loss due to exposure to air and sunlight. This can result in surface cracks that compromise the structural integrity and aesthetics of the concrete. Secondly, for decorative coloured floors, not using plastic sheeting can lead to colour fading and uneven pigmentation due to exposure to sunlight and moisture fluctuations. Thirdly, inadequate curing caused by a lack of protection can weaken the concrete's compressive strength and durability, potentially leading to long-term structural issues and reduced strength.
Additionally, in regions with freezing temperatures, the use of plastic sheeting is crucial to protect the concrete from freezing temperatures and overnight precipitation. Without this protection, the concrete is at risk of scaling and other issues caused by adverse weather conditions.
Furthermore, a concrete foundation without a vapour barrier plastic is prone to decay and cracking. Water vapour can easily penetrate the concrete and damage its foundation, subfloor, and main floor. This can lead to long-term deterioration and potential building failures.
In summary, not using plastic sheeting to cover newly laid concrete can result in several issues, including surface cracks, colour fading, reduced strength, scaling, decay, and potential building failures. Therefore, it is essential to follow the recommended protective measures to ensure the concrete's structural integrity and longevity.
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How long to leave plastic sheeting on for
Plastic sheeting is used to cover concrete to protect it from environmental factors that can compromise its integrity during the curing process. It acts as a protective barrier to prevent moisture loss, temperature fluctuations, and debris accumulation, ensuring the concrete's strength and durability. The ideal time to lay plastic sheeting is immediately after pouring the concrete to maintain a moist surface and an uninterrupted curing process.
However, leaving the plastic sheeting on for too long can have adverse effects. Concrete needs to breathe, and if covered for an extended period, it may cause discoloration and mottling. The best temperature for concrete to cure is around 40 Fahrenheit, and if the temperature is higher, it can lead to excessive moisture retention, resulting in scaling and surface defects. Therefore, it is crucial to monitor the temperature and humidity conditions when using plastic sheeting.
The duration for leaving plastic sheeting on concrete depends on various factors, including ambient temperature, humidity, and the concrete mix design. Typically, it is recommended to keep the plastic sheeting on for at least the first 24 to 48 hours after pouring the concrete. During this initial curing phase, the concrete undergoes the hydration process, absorbing moisture to gain strength.
However, it is important to note that concrete continues to cure and gain strength over time, and removing the plastic sheeting too early can disrupt this process. Ideally, the plastic sheeting should remain in place until the concrete has reached its final set stage, which can take several days to a week or more, depending on the specific concrete mix and environmental conditions.
Removing the plastic sheeting prematurely can lead to inadequate curing, resulting in reduced compressive strength and long-term structural issues. It is crucial to monitor the curing process and make adjustments based on the specific conditions and the advice of concrete professionals or contractors.
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Alternatives to plastic sheeting
Concrete should be covered with plastic sheeting immediately after it has been poured to prevent moisture loss, temperature fluctuations, and debris accumulation. However, if the concrete has an aesthetic quality, using plastic sheeting can be risky as it can cause permanent discolouration. In this case, it may be best to wait for more favourable weather conditions.
Miura Board®
Miura Board® is a 100% recycled, durable alternative to plastic composites. It is a fibre-reinforced composite plastic panel that is stronger and more durable than marine-grade plywood. It is also lightweight and easy to install, requiring no special fixtures.
Polycarbonate Sheets
Polycarbonate sheets are a good alternative to plastic sheeting for roofing and skylights. They are lightweight, durable, and impact-resistant. They can also be used as privacy panels, room partitions, or temporary outdoor signage.
Plywood
Plywood is a more traditional alternative to plastic sheeting for roofing and window coverings. It is a durable and relatively strong material. However, it is not as strong as polycarbonate and may be more susceptible to damage.
Pigmented Stain
A pigmented stain can be used to add colour to concrete. However, this may require a significant alteration of the concrete colour and may not be aesthetically pleasing.
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Frequently asked questions
Concrete curing covers seal off concrete and prevent water from evaporating. They also maintain a certain level of heat and protect the concrete from colder temperatures.
Concrete should be covered with plastic as soon as it is poured, especially if adverse weather conditions such as rain, snow or freezing temperatures are expected.
The plastic covering should be removed after 24 hours, as concrete will be in its steady state and no longer workable after this time. Disposable curing covers can provide constant hydration for up to seven days.
Plastic sheeting can permanently discolour concrete, especially if the sheeting is not laid flat and wrinkles cause discoloration. Plastic should not be applied too early, as this can cause issues with late bleed water.
