If you have had a foundation, sidewalk, or some other section of newly poured concrete, you may wonder when or if the company will remove the forms. You might be ready to see your concrete project without all the concrete formwork, stakes, and braces.
Or maybe you poured it yourself, and you genuinely do not know when you can take your forms off.
Can you leave concrete forms on too long? Keep reading this article to find the answers to all of your questions.
We have put together a comprehensive guide on how long you should wait to take your forms off, how long it takes your concrete structure to cure, and what happens if you leave your forms on for too long.
What are concrete forms?
Your concrete formwork will be made from several different materials, depending on the specific purpose that they are being used for. Forms can be styled, box-like shapes, or containers in which fresh concrete is poured. The type of concrete you have poured may also dictate the type of material and form style used.
Once the form is filled with concrete, you will wait for the concrete to go through the curing process before removing the forms or molding, which is called a strike-off, stripping, or deshuttering. The stripping should only be done once the concrete has gained sufficient strength. At this point, you will see that the concrete is completely dry and taken the shape of the interior styling of your forms.
The term “form” can apply to form boards that make the frame of a newly poured sidewalk or driveway. It could mean the pieces of plywood that are used to form vertical faces. Or it could be talking about preformed cylinders to help pour structural columns, or it could even mean castings for garden statues.
How long will it take the newly poured concrete to dry?
The new concrete will begin to harden in hours, and it will be considered firm within 24 to 48 hours. However, depending on the thickness, location, and type of concrete, this may take longer.
The inspector will have to be present in commercial settings to inspect the concrete surfaces prior to removing formwork can begin.
It will take approximately 28 days for the concrete cure process to reach its full measurable strength, meaning that concrete is completely dry and useable at that time.
Although the concrete may seem as though it is pretty hard after the 48-hour point, it is not hardened enough to use yet. It may be cured enough for allowing foot traffic, but not enough to park heavy equipment.
Here are some factors that dictate how long it will take for the concrete to dry.
- Grade of concrete: The higher the grade of concrete, the faster that it will dry, the quicker that it will gain strength, and the faster it becomes useable.
- Grade of Cement: Cement is used interchangeably with concrete, but it is actually an ingredient in concrete. The higher the cement grade means that the concrete will gain strength and dry faster as well. Avoiding problems such as too much fine material and becoming concrete saturated will help the concrete as well.
- Type of cement: Many different types of cement can have different affects the dry time and strength of concrete: ordinary portland cement, fast-drying cement, low heat cement, and more.
- Temperature: The outside temperature can significantly differ on how quickly or slowly the concrete can harden. In extreme cases of hot weather you will have to examine if the temperature affected its strength.
What if the forms are removed too early?
Depending on what type of pour was done, this can result in several bad things happening.
- Cracking: The concrete slab is not strong enough to support the weight itself, so the concrete can begin to develops large cracks.
- Slumping: If the concrete is not dry enough and still retains some of its liquid characteristics, it can bulge at the edges, or if it’s too runny, it could even run away from itself.
- Collapse: Depending on how the concrete is poured, the concrete can begin to collapse especially if conditions have been temperature affected. If it was poured into vertical faces, foundation wall, or support pillar and is not strong enough to support itself, it can fall apart like wet sand when the forms are removed.
Will the weather affect the dry time?
Cold weather will have huge effects on your concrete and its drying time; if the weather gets cold and drops the temperature of your concrete below 55 degrees, then it will not continue to dry.
Poor conditions like temperature affected concrete slabs will lengthen the dry time and will have to be accounted for. You will need to note how long the temperature was below 55 and add that to your 48-hour time frame, before you can remove concrete formwork.
If the weather brings pouring rain, this can ruin a pour of concrete. It can put too much cold water in the concrete if it is still being poured, but it can also pit and gouge the concrete surface of a smooth concrete job.
Rain can make it almost impossible to achieve a quality concrete pour unless tarps and covers are used to protect the concrete. You will also have to contend with poorly draining soils. Soft ground and other poorly draining soils can be filled with cold water and gather up against your concrete slab. The water will need to be drained away from the concrete if possible.
The heat will also affect your concrete. Extremely hot temperatures will cause it to dry faster than the estimated time.
It is advised that you still wait for the 24 to 48-hour time limit before you remove your forms or molding even if it seems like it has already hardened.
If you’re expecting the temperature to be at scorching levels, you should discuss your plans with a concrete expert before you begin. Extreme heat can affect concrete in different ways, and it is best to get the opinion of an expert to ensure your concrete pour goes smoothly.
The expert may have suggestions such as watering throughout the hottest part of the day until the concrete dries, or else it could shock the concrete. If left unattended it could also begin developing surface crazing, which watering throughout the hottest part of the day would help with.
What if I am pouring concrete in large amounts?
The amount of concrete that you pour or have poured is not necessarily the deciding factor on how long it takes to dry, but it does need to be accounted for.
Pouring a large pad of concrete does take longer to dry, as it is recommended to cure the pad for at least seven days to ensure that the concrete is fully dry before putting any serious weight on it.
Pouring thicker pads and more complex levels of concrete take longer drying times.
When can I remove the forms?
The forms will have very different times between removing them based on what application they were used in. Here we have compiled a list to help show how long you should wait before removing your forms.
- Walls and columns, vertical supports: 24-48 hours
- Slabs with their props left under them: 3-4 days
- Soffits with their props left under them: 7 days
- Props supporting slabs under 15 feet: 7 days
- Props supporting slabs over 15 feet: 14 days
- Props supporting slabs under 20 feet: 14 days
- Props supporting arches and beams over 20 feet: 21 days
When deciding it is formwork stripping time, you will need to consider all of the variables, such as how large of space is being covered, whether it is structural or not, and how thick the concrete is.
Although there isn’t any reason you can’t take them off later than the list above, you should not leave forms in place as they will get in the way of other projects and workers.
Can you leave concrete forms on too long?
There will be varying amounts of time that you will need to leave your forms on when allowing your concrete to harden, but there can be some side effects to leaving them on too long.
In open spaces such as the edges of slabs or outside foundation walls, this will look very poor to leave materials against the concrete. If it stays there for very long, the wood surface will begin to rot and will make the finished product look even worse.
The real problems begin when forming boards are left in contact with the ground.
If there are wooden forms left in any voids underneath your home where they are touching the ground, it can attract termites and other insects and critters.
If you have forms that have not been removed, especially under your home, then the termites and other crittters may start to cause much bigger problems for your home.
Suppose your forms are made of a material other than wood, or you do not have termites in your area. In that case, you should not have any issues with leaving forms in place other than the unappealing appearance and the forms getting in the way of other building components and workers.
How to properly strip concrete forms?
Formwork removal can quickly become one of the most hazardous jobs for concrete work, depending on which type of structures you’re removing the forms from. You should follow all guidelines and suggestions put forth by the American Concrete Institute.
- Test the concrete strength: Ensure that the concrete is dry and can support itself.
- Start at the top: Especially with sloping slabs. Use a hammer to remove nails that hold the forms together.
- The ground and sides: Remove the stakes in the ground using a stake puller. Once loose, the form should pull away easily. If the form has developed a superficial bond, you can use a pry bar, pry upward from the ground, and do not put pressure against the new concrete. Alternate sides to ensure proper release of the concrete. Be gentle with the forms so that they can be dried, cleaned, and reused for future projects.
Tips for not avoiding damage during form stripping.
- Do not use excessive force: Try to avoid using hammers and crowbars, but if you do, try and be gentle with your extractions.
- Ensure concrete strength: It is of the utmost importance that the concrete is of proper strength. If the concrete has not hardened enough, it can crack, slump, or collapse. This can result in costly damages and potential injuries.
- Speak to an engineer: It is highly recommended to seek an engineer’s approval. If you are going to strip concrete forms, then it is highly encouraged that you have a structural engineer inspect the process and deem the forms are ready to be stripped safely.
Depending on what type of concrete is being used, what the final structure of the concrete will be, and what kind of form you used will determine when your forms will be able to be stripped. It is generally not a good idea to leave your forms in place, but it can be done under certain circumstances.
Make sure that you always ensure that your concrete is dry and strong before removing your forms, and when dealing with large and hazardous sections, always be careful when removing the forms. here!