There are quite a few steps involved in building concrete stairs. You need to design the stairs, prepare the foundation, build the formwork, place the reinforcement bars, finish and cure the stairs. Constructing concrete stairs is not an easy task as it involves a lot of engineering and designing, which is best left to an expert. But what if you wish to DIY the construction of the concrete stairs and are a novice?
Then all that you need to do is to read through this article on how to build concrete stairs. This step-by-step guide covers all the detailed aspects, handholding you right from the start till the end. So without much ado, let us get started with the procedure of building concrete stairs.
How to Build Concrete Stairs?
A little bit of site study and design knowledge should be enough to draw the perfect concrete stair design. Here are the factors that go into the design plan. In addition, you may have to check with your local building codes to comply with their dimensions
- Floor height
- Stairs width (usually 3 feet)
- Risers depth (7.5 to 8.25 inches)
- Stair thickness
- Thread width (usually 9 to 9.25 inches)
- Stairs angle (usually 30 to 45 degrees)
- Load on the stair
Figuring the correct step size is essential. Also, consider the handrails.
The riser is the steps vertical face, and the tread is the steps flat face. First, you need to calculate the rise and the run of the steps you plan to construct. To measure the riser, calculate the distance from the ground level to the top or landing platform. For example, if the total rise is 32, then you need four risers of 8 inches.
For the run, usually, every tread is 12 inches in depth for a six or 8-inch rise. The landing step needs to be broad, especially if it leads to an entry.
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Your concrete stairs need the proper support and foundation. It is where the stairs will rest. The base takes the load of the stair and transfers it to the ground, in turn resisting any movement of the stairs.
If there is a plinth beam of the building present at the stairs start, you need to connect the reinforcement steel bars that transfer the stairs load. If there is no plinth beam, then construct a concrete foundation.
The stairs’ width is usually 6 inches wider than the doorway on both sides. Make sure that the ground on the front of the door is level. It should be 6 inches wider than the size of the concrete stairs.
If you build the concrete stairs in the garden or park, remove the topsoil or grass by digging down. It should be done for at least 6 inches. Next, fill the area with crushed rock or gravel. Use a hand tamper to compact the material and get a solid base. If you live in a cold climate, lay 2 inches of Styrofoam down before filling gravel in the hole. It will not let the frost get under the stairs, which may cause the stairs to move.
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Building proper formwork is an important step. The flight angle, thread, and riser dimension have to be checked. When you construct the stairs attached to a wall, you will need to mark the flight line, the risers, and the thread for proper shuttering and formwork fixing.
The boards should be at least 2 inches in thickness to support the concrete weight. You also need 4×4 posts to help the structure. The boards are used for step creation and are fastened with many screws to the formworks lateral structure.
A spirit level lets you check that the form is plumb and level. It is vital to give your staircase a clean look.
To build the forms for your concrete stairs, you may use a ¾ inch plywood. You may also use 2x6s or 2x8s to construct the concrete stairs form. The rise and the run determine the best material. If you are using plywood, then cut it as per the measurement or the stair sides. When you finish the final cut, the plywood should look like the stairs silhouette.
For the 2x8s, first cut the bottom length and then stack the rest of the 2x8s on top of it. The cut should be 12 inches less than the step underneath it. Screw them from all the sides, making use of the 2x4s, and this will give the sides.
Once you do the side forms, place and plumb them and then drive the 2×4 stakes on the outside into the ground to hold them in their place. Next, attach the risers on the side using screws and nails. After you nail the form, stake it, set it in place, and level them using laser or builders level.
Reinforce With Steel
It would help if you had steel bars to reinforce the concrete steps. It will carry the load from the stairs and transfer it to the ground. Here, you may need the help of an engineer who can calculate the size and the number of steel bars depending on the load that comes in the stairs. These steel reinforcement bars should be placed with a minimum of 25mm spacing and tied with each other.
It would help if you poured concrete from below to above. The concrete mix plays a crucial role in determining the durability and strength of the stairs. As a standard rule, you will need three parts of cement, four parts of gravel, and two parts of sand and water. It would help if you used a concrete vibrator when you pour concrete. It will fill the gaps evenly. Do the work with patience and care. If there are any sudden movements, this may disturb the formwork alignment or cause your formwork to collapse.
Start by pouring the concrete first from the bottom step. Next, tap the outside form to consolidate the concrete and spade the concrete using a shovel on the form inside. Do this at each stage. Finally, level with the top of the form until the top of the form is filled.
When you pour concrete, some concrete may sag under the riser. It is fine. Allow the concrete to sit for 20 or 30 minutes and then strike it off. Make sure that it is not sagging and is stiff enough.
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You are free to finish the stairs the way you desire. You can choose to complete it with a float or trowel or give it a concrete, granite, cement, wood, or carpet finish for a better look.
The final finish is what gives the stair its elegance. First, ensure that the concrete is dry so that there is no visible water on its surface. Then, after trowelling it smooth, use a broom to drag it on the surface and give the floor a non-skid texture. Move the riser board and set the concrete such that it does not drip or sag.
After you remove the riser board, trowel the surface. Use a wet sponge to sponge the air pockets and work on the cream. The sponge gives the stairs a different texture.
Keep the concrete wet to cure it. For this, you will have to let the concrete sit for the night. You can then take off the side forms and patch the voids. It is best to use a hose and keep the concrete wet. Two to five days is generally recommended to keep the concrete wet. After a few weeks, apply a concrete sealer to protect the concrete. It also makes cleaning easy.
It takes 21 days for the stairs to dry out completely. You will thus need to keep the formwork for 21 days. Proper curing is done in these 21 days not to let the stairs crack because of thermal expansion. After 21 days, you can remove the formwork using a crowbar and hammer. The step should be done with care to not damage the stair edges or the concrete.
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That is all about building the concrete stairs. Make sure to take the measurement at least two or three times so that you get it right. Some stages could be physically draining, so it is best to ask friends and family for help. Building concrete stairs is fun, and with this guide, you are sure to get it right the first time.