Step-by-step installation of a floor drain - DIY guide

Step-by-step installation of a floor drain – complete guide for DIY installation

The floor drain has become a standard in modern shower enclosures. The reason is not only its clean visual appearance and minimalist look, but above all the truly effective water drainage – even when you take a longer shower or have a stronger water flow. If you have decided to install the drain yourself, this guide will show you the entire process from the first measurement to the final tightness test. It is not simple, but it is not advanced mathematics either – all you need is methodical work, the right tools and a bit of patience.

In practice, we often encounter the fact that most problems with the installation of a floor drain do not occur during the installation of the trap itself, but much earlier – due to a wrong slope design of the floor, a wrong choice of drain location or underestimating the drainage. Therefore, this article does not focus only on "installation" in the narrower sense, but goes through the entire process from the project to the final test.

What you will need: tools, materials and basic knowledge before you start

Before you pick up the angle grinder, make a list. Missing one item can cost you an entire working day, because during wet construction work you cannot simply "run out" for one detail.

Tools

• Water level (at least 120 cm long, ideally 180 cm)
• Laser level – significantly simplifies slope control on a larger area
• Angle grinder with diamond disc (for cutting tiles)
• Hammer drill or demolition hammer (for cutting waste pipe)
• Notched trowel (for applying flexible adhesive to the tiles)
• Mixer and bucket for mortar / screed
• Rubber float
• Measuring tape and marker
• Utility knife or knife for waterproofing
• Paint roller and brush for waterproofing
• Pliers or torque wrench (for tightening the trap)

Materials

• The floor drain itself with trap and grate
• Waste pipe (PVC or HT, DN50 or according to the project)
• Elbows, transitions, seals
• Cement-based screed (S-anhydrite or cement-based, according to the base)
• Waterproofing coating (e.g. two-component dispersion or cement-based)
• Sealing tape for corners (flashing or glass fabric)
• Flexible tile adhesive
• Grout suitable for wet areas
• Sanitary silicone

If you are unsure which diameter of waste pipe to choose, read our article What waste pipe diameter do I need: DN32, DN40 or DN50? – there you will find specific flow calculations and an overview of when DN50 is necessary and when DN40 is sufficient.

Phase 1: Preparation – design of the drain location and waste pipe route

This is the phase where the success of the entire installation is decided. Most people want the drain right next to the wall, because it looks good in pictures. But the location of the drain must respect two basic technical parameters: where the existing waste pipe leads and whether there is enough floor layer thickness to route the pipe with the required slope.

Where to place the drain?

Standardly, the drain is placed along one wall of the shower (side position) or directly opposite the door opening (front position). Both solutions make sense – it depends on the shape of the bathroom and the waste pipe route. For wall installation, there is for example Flexible – Floor drain with edge for perforated grate and adjustable flange to the wall, length 850 mm, which has a special adjustable flange allowing precise seating to the tiling without grouting.

If the shower is symmetrical and you want drainage from both sides (for example in a walk-in shower without a bathtub), look at double-sided floor drain, 750 mm, DOUBLE9 FIT and GO, stainless steel – this allows water to flow in from both sides, which makes it possible to work with a shorter slope.

Waste pipe route

The waste from the drain must be connected to the horizontal sewage pipe in the floor. Here is the rule: the minimum slope of the horizontal pipe is 1–2 % (i.e. 1–2 cm per meter of length). If the connection point is more than 1.5 m away, you will need to calculate the need for a deeper pipe, which increases the requirements for the floor layer thickness.

Important: if the connection point is close (up to 80 cm), you can use a trap with a DN40 outlet and route the pipe almost horizontally. For longer routes, always use DN50 and make sure the pipe is not routed in bends – every elbow over 45° slows down the flow and increases the risk of sedimentation.

Phase 2: Demolition and preparation of the groove for the waste

Once you have planned the route, the physically most demanding part comes – cutting into the concrete slab. If the floor structure is an old apartment (prestressed panels, hollow core slabs), consult a structural engineer or at least the building's construction plan before any demolition. Cutting across the direction of prestressed tendons is never a good idea.

Steps for cutting the groove:

• Mark the pipe route on the floor with a marker, including the width of the groove (pipe diameter + 3–4 cm for bedding)
• Use an angle grinder with a diamond disc to cut the edges of the groove (to prevent crack propagation)
• Use a demolition hammer to remove the material to the required depth
• Depth of the groove = pipe diameter + concrete bedding (minimum 3 cm under the pipe) + thickness of the covering above the pipe
• Clean the groove of dust and debris

Tip from practice: In panel buildings, we repeatedly encountered situations where it was not possible to route the pipe under the floor at all. In such cases, the waste is routed in pre-installed shafts along the wall – not ideal, but functional and hygienically problem-free.

Phase 3: Installing the drain at the correct height

This is a key step where the most mistakes are made. The drain must be installed so that after applying waterproofing, gluing the tiles and grouting, its upper edge (or the upper edge of the grate frame) is in the plane of the tile surface – not even a millimeter higher or lower.

Calculating the installation height of the drain

Practical calculation procedure: measure the thickness of the tile layer (usually 8–12 mm) + the thickness of the adhesive (5–8 mm) + the thickness of the waterproofing layer (1–3 mm). Overall, you should calculate with a height of the layer above the screed of approximately 15–23 mm. The drain body's top edge must be exactly that much lower than the final height of the tiled surface.

Embed the drain into fresh screed or into fast-setting cement mortar. Adjustable feet (if the drain has them) allow for fine height adjustments without the need to remix the mortar. Use a spirit level to check that the drain is level along its entire length – a deviation greater than 2 mm per meter is unacceptable, as water would accumulate at one end.

Phase 4: Connecting to the waste and tightness test before pouring

After placing the drain into the mortar, immediately connect it to the waste pipe. The connection must be rigid and watertight – always use original or manufacturer-recommended gaskets. Improvising with sealing tape or hemp is not acceptable here.

• Insert the trap into the drain body and check that it fits snugly
• Connect the trap's waste outlet to the pipe (either directly or via an elbow)
• The trap can be vertical or side-mounted – check the direction of the outflow before placing the drain
• After connecting, perform a test: pour 2–3 liters of water into the drain and check all connections. There must be no dripping
• Repeat the test after 15 minutes (some gaskets settle)

If the trap is leaking, do not fix it by applying silicone from the outside – water will find a way under the silicone sooner than you expect. Always disassemble, check the gasket, and re-tighten.

Phase 5: Slope layer – the foundation of trouble-free drainage

The slope of the floor towards the drain is the most important technical parameter of the entire shower area. Without the correct slope, water will stand on the floor – and this is not only unpleasant, but also hygienically problematic (mold, dirt).

How much slope do I need?

The recommended slope of the floor towards the drain is 1.5 % to 2 %, which in practice means a drop of 1.5–2 cm for every meter of distance from the drain. Many builders use 1 %, which is the minimum acceptable value – but in standard tiling practice, this is not enough, as irregularities in the grout can effectively cancel out this slope.

Example: A shower area of 120 × 80 cm with a drain along the longer wall. The tiles must have a slope of 1.8 cm from the far wall to the drain. Therefore, the entire screed layer must be shaped with a slope towards the drain.

Techniques for creating the slope

• Sloped screed: Mix cement screed (or S-anhydrite) and apply it with a slope using a straightedge and spirit level. The most classic and reliable solution.
• Slope wedges (slope polystyrene or concrete panels): Ready-made products with built-in slope – fast, but more expensive and sensitive to the evenness of the base.
• Slope adhesive: For small areas and slight slopes, it is possible to compensate for the slope in the adhesive layer itself – but only up to 5 mm in height, otherwise the tiles may peel off.

Important note: the slope layer is applied BEFORE waterproofing. Waterproofing is always applied to a finished, even and sloped base – not the other way around. This is an error we see quite often in practice, and its consequence is moisture penetrating through cracks in the screed directly into the ceiling structure of the lower floor.

Phase 6: Waterproofing – the most important layer you can't see

Waterproofing of the shower area is not optional. It is mandatory by law (STN) and by common sense. Every shower without waterproofing is a time bomb – it's only a matter of years before it starts leaking into the neighbor's apartment or into the ceiling slab.

Waterproofing procedure

• The base must be clean, dry, free of dust and efflorescence
• Apply the base coat of waterproofing compound with a brush (depth base), let it dry according to the manufacturer's instructions (usually 2–4 hours)
• Insert sealing tapes (glass fiber fabric) into the corners wall–floor and wall–wall, press them into the fresh compound
• Apply waterproofing thoroughly around the drain body – the drain must be integrated into the waterproofing plane, not left as an "island"
• Apply the second coat of compound – perpendicular to the first (cross-coating)
• With two-component compound waterproofing, the minimum total dry layer thickness is 2 mm
• Before proceeding, let the waterproofing fully cure (usually 24 hours)

Special attention: the area around the trap is a critical detail. Some gutters have a special sealing gasket that is integrated into the waterproofing layer – if your gutter has such a gasket, use it. If not, apply the waterproofing directly to the gutter flange (edge) and cover at least 3–4 cm.

Phase 7: Laying the sloped tile

Tiling in the shower area is done in the same way as anywhere else, with one essential difference: it must follow the slope of the drain. This means that the adhesive under the tiles is not of uniform thickness – it is thicker near the far wall and thinner near the drain. Therefore, it is necessary to work with a notched trowel and to check each tile with a spirit level in the direction of the slope.

• Use flexible adhesive (C2 or higher) resistant to moisture
• Always apply adhesive to the back of the tile as well (the "butter-coat" method) – air pockets under the tile are a risk in sloped areas
• Cut the last tiles near the drain so that a 2–3 mm gap remains between the tile edge and the drain edge
• This gap is not filled with grout, but with sanitary silicone – to prevent cracking due to temperature changes
• Fill the remaining gaps between tiles in the shower area with flexible, moisture-resistant and mold-resistant grout

Practical tip: when laying the first row of tiles near the drain, use leveling wedges and spacers – they ensure the same height level for adjacent tiles and also maintain the required width of the grout joint.

Phase 8: Final work and functionality test

After the grout and silicone have cured (at least 24 hours, 48 hours for some products), you can proceed with the final operations.

• Insert the grate into the drain – check that it sits evenly and is in line with the tiles
• Perform a final visual inspection: no cracks in the grout, no gaps in the silicone, the grate is properly seated
• Pour 5–10 liters of water into the drain and observe: the drainage must be smooth, without gurgling, without odors, and without any water retention in the shower area
• Gurgling may indicate a vacuum in the pipe or an overly long waste line – in such a case, an air admittance valve (AAV) is needed or the connection to the waste must be verified
• After 48 hours, check the area around the drain from above – there are no dark stains (moisture penetrating through an unfilled gap)

A floor drain as an alternative to a linear drain, for example for smaller shower areas, can be found in our range – for example Floor drain with chrome grid 12×12 cm, DN 40, brass. Read about when a floor drain is a better choice and when a linear drain is better in the article Floor drain vs. linear drain: what is better for a shower area?

Common mistakes during installation of a floor drain and how to avoid them

Over the years of practice, we have seen almost everything. Here is a list of the most common mistakes, so you can avoid them:

• Drain installed too high: The grate protrudes above the tiles → water runs back, risk of tripping, unattractive appearance. Solution: the mortar must be chiseled out, the drain repositioned and regrouted.
• No or insufficient slope: Water stands on the floor. Solution (after tiling): unfortunately, only a complete reconstruction of the floor.
• Waterproofing applied over the trap without integration: Water seeps through the trap into the ceiling below. The most common cause of damage to neighboring ceilings.
• Waste pipe without slope or with reversed slope: Water does not drain or flows back. The pipe must be removed and rerouted.
• Silicone instead of grout everywhere: Silicone is much more prone to mold than flexible grout – use it only where necessary (movable joints, drain-tile connection).
• Short traps without water seal: A trap without a water seal allows odors from the sewer to pass through. Always check whether the trap of your drain has a built-in water seal.

Specifications for different types of shower areas

Shower area without a bathtub (walk-in, directly on the floor)

This is the most common case, where a floor drain is installed. The entire area of the bathroom is in one plane with a slope – either the entire bathroom floor has a slope (a solution for smaller bathrooms), or only the part defined by a glass partition or threshold is sloped. For large walk-in shower areas (over 120 cm wide), consider using a longer drain or two drains for even drainage.

Shower area with a built-in bathtub (threshold)

In this solution, the drain is installed in a higher floor level than the rest of the bathroom. A threshold (usually built from aerated concrete or bricks) separates the shower area. Important: the waterproofing must also extend over the threshold and at least 15 cm into the dry part of the bathroom.

Renovation without demolition (over-renovation)

In some cases, it is not possible to demolish the existing floor (rented apartments, historic buildings). In such cases, there are special solutions – a shower tray with an integrated slope, into which the drain is installed – but this is a special topic that goes beyond the scope of this guide.

Compliance with standards and inspection

In Slovakia, the standard for drainage of buildings is STN EN 12056. For customers, the most relevant is §48a of the building law and the decree on technical requirements for buildings. In practice, this means: if you are doing a bathroom renovation yourself, you are not required to have a building permit (unless you are interfering with load-bearing structures), but you must comply with technical standards. If your renovation compromises the floor's tightness and causes damage to a neighbor's apartment, you will be held responsible.

Therefore: waterproofing, proper slope, and tightness of the waste connection are not recommendations – they are obligations.

Most frequently asked questions (FAQ)

Can I install a floor drain myself without a building permit?

Yes, for a standard bathroom renovation (tile replacement, replacement of fixtures, replacement or addition of drainage equipment), you do not need a building permit – as long as you are not interfering with load-bearing structures or altering the main stack. However, you must still comply with the relevant technical standards (STN), including waterproofing and slope of the waste.

How long does the entire installation of a floor drain, including tiling, take?

For a DIY installation from scratch (including demolition, laying the waste, screeding, waterproofing, and tiling), plan for 5–7 working days. The "wet" work (screeding, waterproofing, tiling) takes 2–3 days, but you must wait for each phase to cure – adding another 2–4 days. Therefore, set aside at least 8–10 days for the bathroom.

What to do if the drain smells?

An odorous drain is almost always caused by evaporation of the water seal in the trap (when the bathroom is not used for a long time) or a defective trap without a water seal. The solution is to pour water into the drain (to restore the water seal). If that doesn't help, check whether the trap has a water seal or whether it is cracked. More information can be found in the article Smelly trap or standing water: causes and solutions.

What length of drain should I choose for an 80 × 120 cm shower area?

For a standard shower area of 80 × 120 cm, an ideal drain length is 700–850 mm. The drain should be 5–10 cm shorter than the wall it is installed against, to allow enough space for the tiling. For an 80 × 80 cm area, a 650–700 mm drain is sufficient. However, the most important thing is the correct diameter of the outlet – for a standard shower area, DN50 is sufficient, but always verify the actual flow rate of your shower.

Do I have to use special adhesive under the tiles in the shower area?

Yes. Regular interior adhesive of class C1 is not suitable for permanently wet areas. The minimum class for a shower area is C2S1 (flexible, water-resistant) according to EN 12004. Even better is C2S2 or two-component epoxy adhesive for ceramic tiles in wet areas – it is more expensive, but guarantees long durability without tiles coming loose.

Can one trap serve a floor drain and a shower drain simultaneously?

No – each fixture (floor drain, bathtub, sink) must have its own trap with a water seal. A connection without a trap is prohibited by standards and is unacceptable from a hygiene perspective, as it would allow direct entry of sewer gases into the interior. For bathtubs, see Automatic bathtub trap with overflow filling, chrome or CLICK/CLACK bathtub trap with removable outlet.

Conclusion: Patience and precision pay off

Installing a floor drain is not a weekend project if you want to do it properly. It requires planning, precise construction preparation, and attention to detail at every stage – from the waste pipe through the slope screed and waterproofing to the final tiling and grouting. If done correctly, however, you will have a bathroom that functions without problems for decades.

At the same time, it is reasonable to entrust certain phases – especially cutting into the concrete slab and connecting to the sewer system – to a professional if you have any doubts. Savings on installation costs can easily be lost in the costs of repairing damage caused by leaks.

If you are comparing whether a floor drain or a traditional floor outlet is more suitable for your case, read the article Floor drain vs. floor outlet – what is better for your type of bathroom. And if you are choosing the right trap, the article How to choose the right trap: sink, bathtub or shower trap? will help you – where you will find an overview of all types of traps along with selection criteria for specific situations.

Do you have a question on this topic?

Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.

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