In modern construction, sunken slabs are commonly used in bathrooms, toilets, and laundry areas to improve drainage and keep plumbing hidden. These slabs are built lower than the main floor to allow proper water flow and prevent flooding.
In this Brick & Bolt blog, we’ll cover everything you need to know about sunken slabs, how they work, their benefits, and how they are built. Keep reading to learn more!
What is a Sunken Slab in Construction?
A sunken slab is built to keep pipes and drainage systems out of sight, making the space look clean and neat. It’s also used for placing air ducts. Usually, it’s placed about 30 cm (12 inches) lower than the normal floor level to allow easy access if something needs fixing.
Lightweight materials such as sand, gravel, or leftover construction bits are placed between the sunken slab and the floor above. These materials should be easy to remove to keep things simple and to protect the pipes. Since sunken slabs are often exposed to water, they need to be made with strong, moisture-resistant materials to avoid damage.
Setting Up Sunken Slab
It is easy to set up the foundation for a sunken slab. Just follow the usual process for making a floor but leave about 300 mm (12 inches) of space above it to add light materials that will protect the sunken slab.
How to Set Up a Sunken Slab:
Step 1: Create the Framework
In the area where the sunken slab will go, lay the framework and TMT bars (steel reinforcement).
Step 2: Prepare the Concrete
Mix cement with waterproofing material to enhance strength and withstand water. Place it in a mould and wait for it to cure.
Step 3: Waterproofing Application
Once cured, spray the top of the slab with a combination of waterproofing material and cement.
Step 4: Plastering
Overlay the slab surface with cement mortar for plastering.
Step 5: Install Flooring
Place tiles using waterproof and anti-shrink adhesive.
Step 6: Seal the Pipes
Seal the sanitary pipe joints using waterproof sealant to prevent leaks. This process ensures the sunken slab is reinforced, strong, water-resistant, and properly protected.
Filling Materials for Sunken Slab
For sunken slabs, several materials are used to make them strong and durable:
- Concrete: This is the main material used for making the slab.
- Reinforcement: Steel bars or mesh are added to reinforce concrete for strength and to avoid cracking.
- Insulation: This can sometimes be provided to keep temperatures steady, with the intent to enhance comfort.
- Waterproofing: A special coating is applied to prevent moisture from damaging or leaking.
The area around the sunken slab must be filled with light material to avoid hindering drainage. Some of them are:
- Broken CLC block: A special type of lightweight block.
- Lightweight cinder: Light, porous material.
- Small broken bricks: Broken pieces from old bricks
- Brick jelly: Small bits of brick, which are in the form of crumbs.
- Small pieces of coal: Chunks of coal
- Burnt lumps of tar: Hard chunks from burnt lumps of tar.
- Concrete AAC blocks: Made from autoclaved aerated concrete.
These materials help make the space safer and lighter and protect the pipes underneath. All these ensure that the slab is stable, water-resistant, and also serves its purpose in due course of time.
Uses of Sunken Slab
Sunken slabs are used in a range of buildings to create extra space between floors and protect the floor below in case of any water leakage. Here are some common uses:
- Bathrooms and Wet Areas
Sunken slabs are often utilised in bathrooms and other wet areas to create a step-down effect. This helps to contain water in a designated area and makes it easier to manage drainage, preventing water from spilling onto the rest of the floor.
- Kitchens
In some households, especially for older designs, the use of sunken slabs in a kitchen separates the cooking area from the dining or living areas to prevent spills in that area while keeping the home’s kitchen different from the other areas of the house.
- Living Rooms
With sunken slabs, a distinctive design can create a special seat or a new floor level inside the living rooms. This enhances the visual impact and can make the area look more interesting and welcoming to inhabit.
- Outdoor Spaces
In outdoor patios, gardens, or swimming pool areas, sunken slabs contribute to water drainage. They seamlessly integrate with other natural surroundings, therefore creating an interesting design element.
Advantages of Sunken Slab
A sunken slab is an intelligent construction method that makes buildings more efficient and convenient. It is simple to construct, budget-friendly, and easy to use. Here are some of its key benefits:
- Hides Pipes Neatly: All plumbing pipes stay hidden, keeping the design of the building clean and uncluttered.
- Clear Plumbing: It reduces the chances of plumbing failure. In case the problem arises, it will cause minimum damage to the floors.
- Budget-Friendly: Sunken slabs are an affordable option that helps save money in the long run.
These make them perfect for being used in bathrooms, kitchens, and areas that need drainage.
Disadvantages of Sunken Slab
While sunken slabs offer many benefits, they also come with some disadvantages:
- The sunken slab increases floor height as it raises the usual floor level.
- Waterproofing Requires Time and Money: Implementing waterproofing processes is expensive and requires more time.
- Needs Skilled Workers: It requires experienced labourers, and they need to spend more time on the construction.
Alternatives to a Sunken Slab
There are other ways to design drainage systems apart from sunken slabs. Here are two common alternatives:
Raised Toilet Floor:
- The toilet floor is raised above the rest of the room to hide the drainage pipes.
- It keeps the pipes out of sight and minimises noise without requiring special plumbing.
- However, it reduces the ceiling height, which may not be comfortable for older people.
Underslung Plumbing:
- Pipes are installed below the slab and hidden above a false ceiling.
- It makes maintenance easier and removes the need for extra filler materials.
- However, special plumbing fixtures are required to reduce noise, thus increasing costs.
Conclusion
Sunken slabs are one of the most practical and useful options for many building projects. They serve to improve drainage and enhance the appearance of a space, which can be expensive and complex to build. Knowing what a sunken slab is and how it works can help you determine whether it’s the right choice for your construction needs.