By Patrick Gordon, technical manager, Splashworks
Installing a toilet on a concrete floor is often seen as a difficult task, but in reality, it’s quite straightforward when approached methodically. Professional plumbers follow a clear process that ensures the toilet is secure, level and properly sealed against leaks. Understanding not just how to do it, but why each step matters, can make all the difference in achieving a long-lasting installation.
All images supplied by Splashworks and Open Source
The process begins with proper preparation. The concrete floor must be clean, dry and level, as any unevenness can lead to instability later on. At the same time, the waste (or soil) pipe should be correctly positioned – either flush with the floor or slightly below it. This alignment is critical because it ensures that the toilet will connect properly to the drainage system without strain or gaps.
Once the area is prepared, the toilet pan is placed loosely over the outlet to check alignment. This step is about precision rather than fixing anything in place. The toilet should sit squarely against the wall and rest evenly on the floor. Using a spirit level helps confirm this. When everything is aligned, the fixing holes at the base of the toilet are marked on the concrete, creating a guide for the next step.
The toilet is then removed so that holes can be drilled into the concrete floor. A masonry drill bit is used to create clean, accurate holes at the marked points. Wall plugs or concrete anchors are inserted into these holes, forming the foundation for a strong mechanical fixing that will hold the toilet securely in place.
Before setting the toilet permanently, a proper seal must be installed. This is typically a wax ring or a rubber seal fitted onto the outlet pipe. Although it may seem like a small detail, this component is essential – it creates a watertight and airtight connection between the toilet and the drain, preventing leaks and unpleasant odours.
With the seal in place, the toilet can be carefully lowered onto the waste pipe and aligned with the drilled holes. Gentle downward pressure ensures the pan sits firmly onto the seal. Bolts or screws are then inserted through the base and tightened into the anchors. It’s important to tighten them evenly and avoid excessive force, as overtightening can crack the ceramic base.
To finish the installation, a neat bead of silicone sealant is applied around the base of the toilet. This serves as a protective barrier against water seeping underneath and also adds a final layer of stability. The cistern, if separate, is then attached, and the water supply is connected. After opening the valve, a few test flushes will confirm whether everything is functioning correctly and free of leaks.
While the correct method is relatively simple, it’s equally important to understand what not to do. One common mistake is attempting to fix the toilet to the floor using mortar. Although it may seem like a solid solution, mortar is actually unsuitable for this purpose.
The main issue with mortar is its rigidity. Toilets and floors naturally expand and shift slightly over time due to temperature changes and regular use. Because mortar cannot accommodate this movement, it tends to crack or loosen, and in some cases, it can even damage the toilet itself. Additionally, using mortar makes future repairs extremely difficult. If the toilet ever needs to be replaced or if a leak develops, removing a mortared unit often results in broken fixtures and damaged flooring.
Mortar also performs poorly as a seal. It is neither flexible nor reliably waterproof, meaning it cannot provide the same protection as a wax ring or rubber seal. Over time, it may allow small leaks to develop, and because it can absorb moisture, it may contribute to unpleasant odours, staining and even bacterial growth around the base of the toilet.
Modern toilets are specifically designed to be installed using mechanical fixings combined with flexible seals. These components work together to provide stability, adaptability and a reliable seal. By bypassing them and using mortar instead, the installation is compromised from the start.
In the end, the best approach is also the simplest: secure the toilet with proper anchors, ensure it is level, and use a flexible seal to prevent leaks. This method not only results in a more durable installation but also makes future maintenance far easier. A properly installed toilet is stable, hygienic and built to last – without unnecessary complications down the line.