Jul 2017 FOOL-PROOF CONCRETE STAIRS
Building experts agree that for masonry homes and offices, concrete stairs are more stable and durable than wooden stairs. Here is the lowdown on building concrete stairs.
It starts with a solid design
Concrete stairs need to meet the following requirements:
- Comply with prescribed building codes and standards;
- At least 90cm wide to allow sufficient space for use;
- It must provide rails;
- An angle and slope that facilitate comfortable use, even by older people; and
- A solid foundation.
Considering the complexities of such a structure, it is best to commission a civil engineer to conduct the design.
Start by building the form according to the design
You will start by building your formwork according to the specifications of the design. Here are some pointers:
CUT AND LAY THE FORMWORK
You can use low-grade plywood such as 2x100mm or 2x180mm to create your formwork, but it is critical to check that it is of sufficient thickness to support the weight of the concrete you are going to pour.
- Cut all the forms for the framework;
- First lay the side forms to create a 2-dimensional side elevation of the stairs.
FASTEN THE FORMWORK
Ideally, the formwork of the concrete stairs should be fastened to both the foundation and the ceiling of the building. For this reason, it is recommended that the ceiling slab and stairs are poured on the same day.
- Use screws to fasten the formwork firmly to the foundation and ceiling slab of the building;
- Check that the steps will bond to the foundation in a seamless connection.
Utilise wooden rods to create braces to resist the outward thrust of the poured concrete. Then nail a sufficient number of rods all along the outer surface of the form.
INSTALL THE RISER FACES
The final step of the formwork is to lay the riser faces.
- Add braces to the centre for stability;
- Ensure that there are no gaps between the boards;
- Use a spirit level to straighten the forms and level the treads.
Ultimately it is important that the entire framework is locked together tightly and securely.
CREATE THE CORRECT CONCRETE MIX
To design the correct concrete mix, you may contact Sephaku Technical Sales for advice on mix design/proportions needed.
One of the most critical parts of creating concrete steps that will last; is using the correct concrete mix. For this type of application, a high strength concrete mix will suffice. For an area of 5 square metres, you will need:
- 2 x 50kg bags of Sephaku 42,5N blended cement
- 2 x 65-litre wheelbarrows of fine sand
- 2 x wheelbarrows of gravel
Mix thoroughly, using enough water to create a mixture that is easily pourable.
POUR THE CONCRETE
- Start at the bottom and work your way up
- Pour only one step at a time
- Spade/vibrate the mix to remove any entrapped air
- Spread the concrete evenly and smooth the surface finish to the desired texture
FINISH THE STEPS
- Level the steps with a screed board or wooden float
- For a finer finish, use a hand / steel trowel
To avoid cracking, you should allow for a curing period of at least two weeks. Click here for best practices on curing techniques (link to our blog article about curing techniques). As soon as the concrete has set, the form boards can be removed with a hammer and crowbar. Just be sure to exercise patience to avoid damaging the stairs’ edges in the process. The supporting formwork at the bottom of the stairs must stay in place until sufficient strength has been achieved, which will most likely be in around 28 days.