Timeline for Pouring a Concrete Countertop
Varying Time Factors: The following steps aim to layout a general timeline but it is important to understand the factors that will cause this time to vary so you can set yourself up for the best results. The number one factor will be environmental conditions. When we say “normal conditions” this refers to an indoor controlled environment with relatively low humidity and a temperature between 70-75ºF. Warm temperatures will accelerate the cure time while cool temperatures will have the opposite effect. The same goes for the temperature of the water used to mix the concrete. To retard the mix, cold water should be used. If using water from a hose and the hose is sitting in the sun, this warm water can cause the mix to set rapidly. If pouring outdoors, direct sunlight will rapidly accelerate the cure process as well so make sure to use cold water and work during hours of the day where the temperatures are cooler and the sunlight is least intense. Also, high wind movement will cause the surface of the concrete to dry faster than the interior so you may need to float more often in order to keep a creamier top. The other major factor will be the amount of water used in the concrete. We give recommendations but this will also vary depending on these certain factors. The more water used in the concrete to achieve a pourable consistency, the longer the concrete will take to set before you can float or steel trowel. That is why below we will describe the things to look for to know when it’s time for each step.
Mixing and Placing Concrete: Whether you are using our Liqui-Crete/ Counter-Pack additive or White Concrete Countertop Mix, always follow the mixing instructions on the packaging or they can also be found online. Both products have videos showing proper mixing and desired consistencies. When placing the concrete for cast-in-place, always start at one end and work to the other. Screed the concrete as you go to make sure the forms are filled right to the top. You may need to go back and add some concrete in certain areas if it appears low. If your pour is fairly large, you may need to start floating at one end while you are still pouring at the other so extra helping hands are always desirable.
Magnesium float: You will use a Magnesium float (Lexan float advised on white concrete) about 30-60 minutes after the concrete is placed, when it starts to have a dull, dry look. Again, this timing will vary depending on several factors. Using the float will help you to get a smooth flat surface but it will leave the concrete slightly textured. This is crucial so that evaporation can continue to happen properly. The float will give you a creamier concrete as it pulls more bleed water to the surface. If the surface begins to crust over but the concrete still seems too soft for a steel trowel, you can use the float again. This will bring the cream back to the surface and give the concrete a longer time to set up before you steel trowel.
Steel Trowel: in normal conditions, your concrete should be ready for a first steel trowel (chrome trowel advised on white concrete) between the 2 and 4 hour mark. After you have used the magnesium float and the creamy surface has gone back to the dull, dry look, it should be ready. There should never be any soft cream or bleed water present when steel troweling. The concrete should feel fairly firm, like dense rubber, to the touch. A light finger press should leave little to no indentation. If you begin troweling and are leaving lots of trowel lines with moderate pressure, the concrete is likely too soft and you can use the magnesium float again to undo this troweling. When the concrete is ready, firm pressure with the steel trowel should leave almost no marks in the concrete. Prematurely using the steel trowel will close off the concrete and not allow proper water evaporation. This is the leading cause for a soft, dusty finish (known as laitance) which we want to avoid. After steel troweling once, you can wait another 1-2 hours until the concrete is very firm (too set to leave any indentation). A final troweling at this point will help you get a very smooth or burnished finish. Care must be taken not to gouge the concrete as little can be done to repair it at this point. Using a trowel lubricant, such as Z Trowel-Slick, will make your trowel glide much easier over the firm concrete. Often, people will use water but this should be avoided as troweling excess water back into your concrete can cause surface issues.
Snap off forms: In most conditions, you can snap off the forms a full 24 hours after the pour. If temperatures are low, waiting longer is advisable. You will use our Gem Pad (or other abrasives) to sand the tops of the forms before snapping them off to remove any excess concrete on the lip. Use your fingers to separate the form from the concrete. Then you will pull the forms downward until they snap off.
Curing: In most cases, with normal conditions, the concrete can now be left alone to cure. In ideal indoor conditions, no plastic or additional moisture is necessary when using our concrete mix products, they are designed to reduce shrinking and curling. When pouring outside in direct sunlight or pouring in high temperatures, it can be helpful to wet cure or cover with plastic to keep moisture in. This will retain moisture and slow down the curing process to prevent curling.
Begin to sand: You can sand/polish your concrete countertop about 2-3 days after the pour. Again, environmental factors, the type of concrete used and the amount of water used will all effect the early cure strength. If your concrete still feels a little soft and you can easily scratch it with your fingernail, it is most likely too soon to sand. Use your discretion as to the grit of sandpaper and how much you need to sand. We normally will use between 80-220 grit depending on the concrete surface. The idea is to remove any minor imperfections and help “open” the pores of the concrete before staining and sealing. You should also make sure to sand the entire top uniformly as variations in surface texture will affect how stain and sealer penetrate. If you plan to wet polish, this should be done on day 2-5. Waiting longer will not hurt the concrete but it will make the polishing process more difficult as the concrete will be much harder one week after the pour.
Apply stain: This step is optional. In normal conditions, you can begin to stain around day 3. Before staining the concrete should be all one light (relatively) uniform color. Any dark areas are a good indicator that there is still excess moisture in the concrete that may prohibit your colors from displaying correctly or the stain from absorbing properly. Before staining make sure the concrete is clean. You will need to wipe your entire countertop down with a wet cloth and remove any dust or debris that may be left on the top. There are unlimited methods and techniques for applying stain so we highly recommend practicing on a sample piece first to find what works for you depending on the look you are trying to achieve. Wetting the concrete first is not required but it will slow the absorption of the stain into the concrete, giving you more working time and allowing colors to bleed together to create more natural looking variations. Freshly cured concrete is very “thirsty” for water so if you brush or roll stain over dry concrete it may absorb rather quickly leaving you with unnatural lines or streaks.
Sealing: Depending on which sealer you choose, will determine on when you can begin application. It is important to understand what type of sealer you are using and how it works in order to guarantee best results. For example, a penetrating, breathable sealer, like our SiAcryl 14, may be safe to apply 4 days after the pour but because of the moisture left in the concrete, you will get better results if you wait 5-10 days. Whereas an epoxy resin sealer like our Aqua-Poxy requires that the concrete has no moisture present at all or you may risk delamination. We recommend a minimum of 10 days after the pour. Always consult the instructions for proper application times and techniques. If you have any questions we are always happy to help via email or phone.