This article is about how to build a concrete ceiling. Pouring a concrete ceiling is not a common technique in United States, but is used on a large scale in Europe. Nevertheless, although it is more expensive and it takes longer as compared to a wood stud ceiling, it still has a few advantages which could make you think again when building your house. Consequently, when building a concrete ceiling the rigidity of your house will be much better and it could support more weight, as compared to light constructions. On the other hand, a concrete ceiling is so strong and durable, that you won’t hear any footsteps when sitting on the ground floor.
Building a concrete ceiling will increase the phonic insulation and durability of your house. But these advantages come together with a few drawbacks, such as the higher cost of the project or the fact that pouring a concrete ceiling may take up to several months, until you can actually build the walls and the roof. In addition, you have to build a formwork to be able to build the concrete ceiling.
Pouring a concrete ceiling is difficult without the help of a qualified engineer. In addition, you have to observe your local codes in order to get the construction permits. The thickness of the concrete ceilings varies according to the weight it has to support, but it is usually between 5-6” for residential constructions. Taking into consideration the weight of the rebar structure, as well as the weight of the concrete, building a sturdy form is essential for any project. Therefore, use thick wooden boards or panels to build the form and support the whole structure with 4×4 posts.
In order to build a concrete ceiling, you need the following:
- 1×4 wood boards for building the formworks / tego plywood boards
- 4×4 wood posts to support the ceiling / adjustable metal posts
- Nails/wood screws to fasten the formwork
- Safety gloves, glasses
- Measuring tape, carpentry pencil, l-square
- Circular saw/jigsaw to build the formwork
- Use boots, as not to get your cloths and skin dirty with concrete
- Clean thoroughly your tools after you have finished the project
- Wear protective glasses and gloves, to avoid possible injuries
- Make sure the ceiling formwork is perfectly level
- Few hours up to a day, according to the surface of your foundation and the number of workers
Building a formwork for the concrete ceiling
In order to build the concrete ceiling, one has to make a proper formwork. Building the formwork is a complex process, but anyone can do a job in a professional manner, provided it has some experience in working with lumber.
The complete details of the formwork, as well as of the reinforcing structure, have to be provided in the plans of your house. Remember that building a concrete ceiling is essential for the durability of your house, so you have to consult a qualified professional before starting such a project. In addition, you have to observe your local codes and get all the needed construction permits, as your safety is at stake.
Smart Tip: when building the formwork, you have to use pressure-treated lumber, as to make sure it will support the weight of the reinforcing bars, as well as the concrete.
As you can see in these images, you have to build first the frame of the formwork, by using 4×4 lumber. On this structure you should install 2×4 wooden boards or tego plywood boards. The first option is better for the ones with a tight budget, but we recommend you to use tego plywood boards as the bottom of the ceiling will be perfectly straight, and you won’t have to put extra-effort to make it level.
If you are using wooden boards, you have to make sure they are straight and in a good condition. In addition, make sure you don’t leave gaps between the wooden boards, as the concrete might leak.
You can see the ceiling form from inside of the house, as to get a better grasp of the procedure. It might look unusual for the vast majority of you, but this is the proper way of pouring a concrete ceiling. You should notice that there are many 4×4 posts installed every 15”, in both directions, as to support the weight of the reinforcing structure and of the concrete.
Smart Tip: Rent adjustable metal posts when building your concrete ceiling. They support more weight and adjust to the height of your rooms.
We have drawn this sketch, as to show you in detail, how it should look the structure of the ceiling formwork. As we have already said, these details will be provided by the architects, but we want to get you accustomed to these construction techniques.
If you are using 4×4 posts, you have to thoroughly fasten them to the structure of your ceiling. Consequently you should use a 2×4 lumber and a few nails to lock them firmly. Use a level to make sure the 4×4 posts are plumb.
Building reinforcing structure for the concrete ceiling
After you have built the formwork for pouring the concrete ceiling, you have to build and lock into position the reinforcing structure. As the concrete ceiling is almost floating, being supported only by several walls and pillars, you have to use a lot of rebars (the architect will compute the needed amount of rebars)
In this image you can see a close-up with the reinforcing structure of the concrete ceiling. You might have noticed the rebar beams and you might ask yourself about their purpose. The rebar beams are placed on top of the walls and are connected with the rest of the reinforcing structure of the concrete ceiling. In this way, the concrete ceiling will be supported by the walls and will be more rigid and durable.
In this image you can see the reinforcing structure around the stairways. You could notice that we have used many rebars around the stairs and alongside walls.
How to pour a concrete ceiling
After you have installed the formwork and the reinforcing structure, you have to pour concrete, as to finish the ceiling. Consequently, you should rent a concrete pomp and several hoses, to pour the concrete in the ceiling formwork.
In addition, you should order the needed amount of concrete from your local concrete company (they will deliver it with trucks). You should know that there are more types of concrete, so make sure you order the one which is indicated in your structural plans (usually for ceilings you have to use B 250). Ideally, you should hire an engineer to supervise the workers while they pour the concrete ceiling.
After you have poured concrete in the formwork, you have to finish it with a bull float from one end to the other. But first you should vibrate the concrete, as to make sure there are no pockets of air left in the concrete ceiling.
After you have used the concrete vibrator, you should finish the concrete surface with a bull float. Make sure you finish the surface properly, making sure it is perfectly level. Nevertheless, in most of the cases you will have to pour screed after the concrete ceiling has dried out to make it perfectly level.
Next, you have to wait a couple of months until the concrete ceiling has dried out completely. After the ceiling has dried, you can remove the formwork and continue building the walls and the rest of your house.
Make sure you sprinkle water over the concrete ceiling, otherwise the ceiling will crack. In the worst case, you might even redo the concrete ceiling, if the cracks are too deep (the cracks might affect the rigidity of the ceiling).
After the ceiling has dried out properly, you can start building the walls and the roof of your house. Pouring a concrete ceiling is not very difficult if you follow the guidelines from your structural plans.