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  • Slabs & foundations
  • 25–30 MPa

Rib and Block Slab in South Africa: Free Quotes from Local Suppliers

Need a rib and block slab? Tell us what you need and independent South African suppliers and builders will send a free quote. No fee, no obligation.

  • Quotes fromrib and block suppliers and installers
  • Areaall nine provinces
  • Cost to youfree

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Builders placing hollow concrete blocks between precast ribs on a first floor with props underneath
Builders placing hollow concrete blocks between precast ribs on a first floor with props underneath

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Tell us what you need and where. A contractor or supplier who works in your area quotes you directly. Free, no obligation.

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Length and width in metres, thickness in millimetres. Add a row for each slab, footing or path. The totals go into your request.

#Length mWidth mThick mmQty
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0m³ concrete
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Order about 5–10% more than the net volume to allow for waste and uneven ground.

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A rib and block slab is a light, economical suspended floor made of precast ribs, hollow infill blocks and a layer of concrete poured on top. It is the most common first-floor and roof system on South African houses. ConcreteSlab.co.za is a free quote service. You fill in one form and we pass your request to independent rib-and-block suppliers, contractors and builders' merchants in your area, who quote you directly. We do not make, sell, deliver or install slabs. There is no fee and no obligation.

How a rib and block slab works

The system has three parts. Precast prestressed or reinforced ribs span between the supporting walls or beams. Hollow concrete or polystyrene blocks sit between the ribs and act as permanent formwork. A concrete topping, usually with light mesh, is poured over the top and binds everything together.

The ribs carry the load, so the slab is light for its span. Because the blocks are hollow, the floor uses far less concrete than a solid slab and is easy to handle on site with few workers and no heavy crane.

The supplier usually delivers ribs and blocks cut to length, ready to lay.

Spans, depths and design

An engineer must design a suspended slab. The design sets the rib size, the spacing, the depth and the topping, and it depends on the span and the load.

  • Depth: common systems range from about 170 mm to 255 mm overall, including a topping of around 50 mm.
  • Span: longer spans need deeper ribs or closer spacing, and sometimes a beam in the middle.
  • Loads: a bedroom floor, a tiled bathroom, a water tank and a roof garden are all different.
  • Standards: design follows SANS 10100-1, and your plans follow SANS 10400.

Never reduce the specified props or the curing time to save a few days.

Installing it on site

Good installation matters as much as the design. Walls or beams must be level and strong enough before the ribs are laid. Props go under the ribs, and the supplier or engineer will say how many and for how long.

  • Bearing: ribs must sit properly on the supports, as shown on the drawings.
  • Topping: use concrete to the specified strength, usually 25 MPa or more, supplied to SANS 878.
  • Services: plan electrical conduit and plumbing sleeves before the topping goes on.
  • Curing: keep the topping damp and leave props in place until the engineer allows removal.

For a first floor, a concrete pump is often used to lift the topping up.

What affects your quote

People search for the rib and block slab price or a price per square metre, but it depends on the job. We never give prices here. Suppliers will look at:

  • The floor area, spans and engineer's design.
  • Block type: concrete or polystyrene.
  • Delivery distance and offloading, including a crane or truck-mounted offload if needed.
  • Prop hire, mesh and topping concrete.
  • Whether you want supply only or supply and installation.

Send your engineer's drawing with your request for the clearest quotes.

Comparing quotes for rib and block slabs

The lowest figure is not always the best deal. When your quotes arrive, check:

  • Specification: the thickness, the concrete strength in MPa, the steel and the membrane, so every quote is for the same work.
  • Preparation: excavation, sub-base compaction, shuttering and who removes spoil and rubble.
  • Concrete and access: ready-mix or site-mixed, whether a pump is included and any part-load or waiting charges.
  • Finish, curing and guarantee: the surface finish, how long it will be cured, where joints are cut and what guarantee covers the work.

What to include in your request

  • Attach the engineer's drawing or give the spans and floor area.
  • State whether the slab is a first floor or a roof.
  • Choose concrete or polystyrene blocks, if you have a preference.
  • Say how the load will be offloaded: truck access, crane or by hand.
  • Add your town and the date you need the slab.

Frequently asked questions

Does ConcreteSlab.co.za supply rib and block slabs?
No. ConcreteSlab.co.za is a free quote service. You send one request and we pass it to independent rib-and-block suppliers, contractors and builders' merchants near you. They contact you directly with a quote. We do not make, sell, deliver or install slabs, and there is no obligation.
What is a rib and block slab?
It is a suspended floor made of precast ribs with hollow blocks between them and a concrete topping poured over the top. It is lighter than a solid slab and quick to build. It is widely used for first floors and roofs on South African houses.
Do I need an engineer for a rib and block slab?
Yes. A suspended slab must be designed by a competent person, usually a registered engineer. The design fixes the ribs, spacing, depth and topping for your span and loads. Your municipality and the NHBRC for new homes will expect the engineer's drawings with your plans.
How long do the props stay in place?
Props stay until the engineer says the topping has reached enough strength, often at least a couple of weeks. Do not remove them early, and do not load the floor with stacked bricks or sand before then. Curing in hot or cold weather can change the timing.

Rib and Block Slabs by province

Rib and Block Slabs by city and town

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