First-floor concrete slabs -What you need to know.

All new residential building projects must have a set of approved building plans and with that, your architect would have appointed a building engineer that is responsible for the design and layout of the concrete slabs on your building project.

If you are in the market for a new first-floor concrete slab there are two things you need before you can request a quotation from a concrete slab specialist, and that is:

1. The architectural build plans and,
2. The engineer’s slab design and layout.

The slab design will also include the bending schedule of the reinforcement for the concrete slab and must be included with the documents you send to the slab specialists when requesting a quote, but how do you select the best concrete slab specialist?

Choosing a slab specialist

Everyone has a different approach to this but it all boils down to, if the slab specialist you select can do the job and if they can be trusted not run away with your money. When I look for a new supplier of any service I first do a search online checking location, websites, numbers, emails, and reviews. Once I have selected between 3 and 5 concrete slab specialist I will call them up and based on their response time and feedback I will select a few to give me a quotation. Word of mouth is also very important, so ask your friend or colleges if they know a slab specialist and what their experience was. Trust your gut on this one, if your inner voice speaks to you, listen.

First-floor slab specialists in Pretoria

Within the ECO Built group, we have experienced partners that have a combined experience of more than 30 years and the projects to proof it. We can help you to get quotes from trusted concrete slab specialists in Pretoria. Explore the first-floor slab project installed by our slab specialists in the project section of the ECO Built website. Now let’s take a look at what is needed to design and construct the first-floor slab.

First-floor slab design

Concrete slab design consists of two parts,

1. Structural design and
2. Casting & layout design.

The concrete slab design and detailing is done by a qualified building engineer. The reinforced concrete slab design includes the guidelines for the depth of the slab, the span of the slab, loads on slab and reinforcement required by the slab.

Detailing of a reinforced concrete slab include nominal cover, minimum reinforcement required, the spacing of bars, maximum diameter of bars and the bending schedule.

Casting and layout of reinforced concrete slab include pre-construction planning, construction practices, and joint layouts and are coordinated by the concrete slab specialist.

Reinforced concrete slab & Suspended slabs construction

A concrete slab is a very important structural element of your house and provides a flat, usable service to build on. A suspended slab is a slab that has at least two of its opposite edges supported by walls, beams or columns and are not in direct contact with the ground.

Concrete slabs can be prefabricated off-site and installed or poured in situ on site. Form-work is required to construct the in situ concrete slabs and hold the wet concrete. Once the reinforced steel bars are in place and all-electric conduit and services are installed concrete can be poured to create the reinforced concrete slab.

The construction process of reinforced concrete slab & suspended slabs include:

1. Erection of formwork;
2. Placement of reinforcement steel bars;
3. Pouring of concrete;
4. Compacting and finishing concrete;
5. Curing of the concrete slab;
6. Removal of formwork.

The curing process is also monitored by the concrete slab specialist and the concrete must not be allowed to dry out or freeze.

First-floor slab thickness

The normal thickness used for reinforced concrete slabs in South Africa is 170 mm for small slabs, 255 mm for slabs larger than 5m x 5m and 340 mm thick for long-span slabs forming part of a beam and carrying heavier loads. The thickness of a slab will depend on the use and span of the slab. The exact thickness of the slab will be calculated by the engineer that designed the reinforcement for the concrete slab.

Pouring concrete slab on the first floor

Before the concrete can be poured in-situ to create the suspended first-floor concrete slab formwork and shuttering must be erected as follow:

1. Construct a temporary structure using struts, beams and shuttering below the slab position;
2. Build the formwork on top of the structure to hold the concrete in place;
3. Assemble reinforcement as indicated by building engineer guidelines;
4. Install all services like water, electric and drainage pipes;
5. Pour concrete in-situ into the formwork by using a boomed concrete pump;
6. Let the concrete cure for a few days while keeping it wet & frost-free;
7. Once the concrete has cured and the correct strength has been reached the supporting structure and formwork can be removed.

Once the concrete has cured (usually within 10 days) you can start building. However, waiting a bit longer can help prevent the concrete from cracking as it takes up to 28 days after it was poured to reach its maximum strength.

What is the aftercare of a newly poured concrete slab?

It takes up to 28 days for a newly poured concrete slab to get to its maximum strength. It is very important to keep moister in the slab over this period to ensure that the chemical reaction between the cement and water that binds the mixture, also known as hydration can take place. If the water evaporates too quickly from the service this will prevent the correct curing process from taking place weakening the structure and causing cracking. It is equally important to prevent the concrete slab from freezing over as this will put the slab under stress and cause cracking.

It is also advisable to keep foot traffic off the slab for the first 24 hours. Building activities must not take place for a minimum of ten days nor must the slab be subjected to excessive weight.

Cost of a first-floor concrete slab

According to South African estimators, the square meter pricing for a suspended first floor concrete slabs starts at R850.00 per square meter depending on the engineer’s design. Each slab has its own design and requirements so for an accurate quote you would have to contact a concrete slab specialist and request a quote from them

Do you need a concrete slab for your building project?

ECO Built’s slab construction division has experience with design, implement, inspect & certification within the concrete slabs & roof slab industry. We specialize in tackling challenging projects, specializing in raft foundations, in-situ first-floor concrete slabs, beams, staircases, basements, retaining walls and concrete columns. Request a competitive quote from one of our partners today.