To fill and seal non-structural crack and cavities in structural concrete such as concrete decks, balconies, concrete roof structures, wet room, swimming pool and especially before waterproofing works. (TDS p.1)
- Pack
- 160 mL and 850 mL set
Step-by-step solution
Toilet or bathroom leaking into the ceiling below
Seelan, drips or falling plaster on the ceiling under an upstairs bathroom. Find the source, fix it from the bathroom side, then dry and repair the ceiling slab below.
- 6 steps
- 8 products
- 4 answers
You need this when…
- Wet patch, drips or bubbling paint on the ceiling under a bathroom
- The stain grows after showers or toilet flushes
- Falling plaster, rust stains or exposed steel in the ceiling
- Sewage smell in the room below
- Leak continues even when the bathroom is not used (points to a supply pipe)
The work, step by step
General guidance based on the manufacturer data sheets. Site conditions differ: confirm the system with MCT before you start. Where we do not name a product, ask us and we will confirm the right one.
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Step 1: Find the source
Close all taps and watch the water meter: a leak with no use points to a supply pipe. Then water-test the WC connection, floor trap, drain joints and shower floor one at a time. Plumbing faults are fixed first; no coating stops a leaking pipe.
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Step 2: Quick repair from above (floor still sound)
Rake out the floor grout and refill leaking tile joints with Sikadur-20 Crack Seal, which lists repairing floor tile joints for leakage in wet rooms (p.1); joints must be clean and free of water (p.2). Regrout the rest with an epoxy grout for wet rooms (SikaCeram-850 Design p.1). Reseal the WC base, trap and wall-floor corners with Sikasil-715 WS (p.1).
Sikadur-20 Crack Seal Sika Request a quotation SikaCeram-850 Design Sika Grouting tiles for the following interior residential and commercial building applications: Wet rooms, Shopping malls, Hospitals, Commercial / Industrial kitchens, Food industry, Swimming pools (indoors). (TDS p.1)
- Temperature stated in TDS
- +5 °C min. / +35 °C max (TDS p.2)
- Pack
- 400 ml double side-by-side cartridge
Sikasil-715 WS Sika Sikasil®-715 WS is designed for weather proofing and sealing applications where durability under severe conditions is required. (TDS p.1)
- Temperature stated in TDS
- +5 °C to +40 °C (TDS p.2)
- Pack
- 300 ml cartridge, 12 cartridges per box
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Step 3: Full repair from above (leak persists or tiles hollow)
Strip and redo as in the Bathroom waterproofing guide: crack sealing, SikaTop-550 Seal under the tiles (wet areas under tiling, p.1), then re-tiling with SikaCeram-205 PK (p.1).
SikaTop-550 Seal Sika As a waterproof lining for water retaining structures. (TDS p.1)
- Temperature stated in TDS
- +5°C min. / 40°C max (TDS p.2)
Other options for this stepAsk us The right product here depends on your site. We confirm it before naming it.
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Step 4: Stop a drip through the slab
Only if water still comes through a slab crack after the source is fixed: inject from below with Sika Injection-306, which seals water-bearing cracks and leaks with minor movement (p.1). It is for experienced professionals only (p.1), and nearby pipes must be located first (p.2).
Sika Injection-306 Sika Professionals only Request a quotation Crack and joint injection Injection of SikaFuko® injection hoses to seal construction joints Sealing water-bearing cracks and voids Sealing all types of leaking building components in damp or water saturated ground conditions Sealing leaks where there is so… (TDS p.1)
- Temperature stated in TDS
- +5 °C min. / +40 °C max (TDS p.2)
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Step 5: Dry out and repair the ceiling slab
Let the slab dry. Cut out loose plaster and damaged concrete and clean rusted steel. Coat the steel with Sika MonoTop-610, a bonding primer and corrosion protection for experienced professionals (p.1), and rebuild with Sika MonoTop-612 PK, which suits overhead work (p.1). If steel has lost section or the slab sags, an engineer must assess it.
Sika MonoTop-610 Sika Professionals only Bonding primer as part of a concrete repair system Reinforcement corrosion protection as part of a concrete repair system (TDS p.1)
Sika MonoTop-612 PK Sika Sika MonoTop®-612 PK is used for structural concrete repairs as well as general patching to concrete and mortars. (TDS p.1)
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Step 6: Finish the ceiling
Close pores and smooth the repair with SikaRep Fine PK, a pore sealer and finishing mortar (p.1), then plaster and paint once dry.
SikaRep Fine PK Sika SikaRep® Fine PK can be used as a: Pore sealer / finishing mortar on cementitious substrates, Thin layer rendering on horizontal and vertical areas in building and civil engineering construction, for external and internal finishing etc, Levelling mortar on uneven substrates, and profiled concrete… (TDS p.1)
Proposal brief
Toilet or bathroom leaking into the ceiling below: scope and system
A starting point for a site proposal. Quantities, prices and the final specification follow a site visit or photos.
Scope of work
- Leak tracing with the plumber (supply, drain, floor)
- Bathroom-side repair: tile joint sealing and regrouting, or full re-waterproofing
- Crack injection from below where needed
- Ceiling slab repair: steel cleaning and priming, repair mortar, finishing mortar
- Re-plastering and painting (optional)
System build-up
| Step | Product | Pack | Source |
|---|---|---|---|
| 2. Quick repair from above (floor still sound) | Sikadur-20 Crack Seal | 160 mL and 850 mL set | TDS p.1 · March 2025, Version 03.02 |
| 2. Quick repair from above (floor still sound) | SikaCeram-850 Design | 400 ml double side-by-side cartridge | TDS p.1 · April 2025, Version 01.01 |
| 2. Quick repair from above (floor still sound) | Sikasil-715 WS | 300 ml cartridge, 12 cartridges per box | TDS p.1 · May 2025, Version 03.01 |
| 3. Full repair from above (leak persists or tiles hollow) | SikaTop-550 Seal | — | TDS p.1 · March 2024, Version 01.01 |
| 4. Stop a drip through the slab | Sika Injection-306 (professionals) | — | TDS p.1 · May 2021, Version 02.01 |
| 5. Dry out and repair the ceiling slab | Sika MonoTop-610 (professionals) | — | TDS p.1 · May 2021, Version 01.01 |
| 5. Dry out and repair the ceiling slab | Sika MonoTop-612 PK | — | TDS p.1 · October 2023, Version 01.02 |
| 6. Finish the ceiling | SikaRep Fine PK | — | TDS p.1 · October 2023, Version 01.03 |
What we need from you
- Photos of the ceiling stain and of the bathroom above
- When the leak appears (always, or only after use)
- Age of the bathroom and any past repairs
- Access to the bathroom above (same owner or neighbour?)
Site conditions
- Plumbing faults repaired before waterproofing
- Slab allowed to dry before ceiling repair and painting
- Bathroom out of use during the repair
Not included
- Plumbing and sanitaryware replacement
- Structural repair of the slab (quoted after an engineer's assessment)
- False-ceiling and electrical work
Questions customers ask
Can it be fixed from below without touching the bathroom?
Not reliably, because the water enters from the bathroom side. Injection from below can stop a drip through a crack (Sika Injection-306 p.1), but the source above must be fixed. Ask us: it depends on site conditions.
Do we have to break all the bathroom tiles?
Not always. If the floor is sound, leaking tile joints can be repaired with Sikadur-20 Crack Seal (p.1) and the grout renewed. If leaks continue, a full re-waterproofing is needed.
There is rusty steel showing in the ceiling. Is that serious?
Rusting steel must be cleaned and protected: Sika MonoTop-610 is a reinforcement corrosion protection in a repair system (p.1). If the steel has lost section or the slab sags, an engineer must assess it before repair.
How long before we can paint the ceiling?
The slab must dry first; the time depends on how wet it is. Ask us: it depends on site conditions.
Steps and product facts are taken from the manufacturer data sheets (page cited). Products are named only where the data sheet confirms the use; quantities follow a site visit or photos. General guidance: check the data sheet or ask us before you start.