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
Terrace and balcony waterproofing
Balconies, terraces and open verandas that people walk on, usually finished with tiles. The waterproofing goes under the tile bed and turns up at walls, door thresholds and drains.
- 6 steps
- 4 products
- 4 answers
You need this when…
- Damp or stains on the ceiling below the balcony
- Water seeping under the door threshold into the room
- White salt deposits on the balcony soffit or edge
- Loose or hollow-sounding tiles
- Water draining towards the wall instead of the outlet
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: Strip and check the falls
Remove failed tiles and screed. Check that the floor falls away from the door towards the outlet, and correct the falls in the screed if needed. The cement base must be at least 28 days old before tiling (SikaCeram-205 PK p.2).
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Step 2: Seal cracks
Fill non-structural cracks before waterproofing. The data sheet lists balconies and concrete decks (Sikadur-20 Crack Seal p.1). The concrete must be at least 28 days old and the cracks no wider than 10 mm (Sikadur-20 Crack Seal p.2).
Sikadur-20 Crack Seal Sika Request a quotation -
Step 3: Apply the waterproofing slurry
Prepare to a sound base with at least 1.0 N/mm² pull-off, then pre-dampen it. Apply at least 2 coats of 1–2 mm each (SikaSeal-105 PK p.1, p.2). SikaTop-107 Seal PK also lists balconies and terraces (SikaTop-107 Seal PK p.1). Carry the coat up the walls, under the door threshold and into the outlet.
SikaSeal-105 PK Sika SikaSeal®-105 PK is used as an economical and easy to use as waterproofing slurry both for external and internal applications. SikaSeal®-105 PK is suitable for the following applications: Water and sewage works, such as tanks and manholes, Basements and lift pits, Retaining walls and bridge struc… (TDS p.1)
- Temperature stated in TDS
- +5 °C min. / +40 °C max (TDS p.2)
SikaTop-107 Seal PK Sika For external and internal waterproofing, on concrete, mortar, brickwork, and steel in: Basements, Swimming pools, Water tanks, Flat roofs, Balconies, terraces, Bridges. (TDS p.1)
- Temperature stated in TDS
- +5 °C min. / +35 °C max (TDS p.2)
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Step 4: Seal wall joints, posts and fixings
Seal the wall-floor and frame connections with an elastic sealant that lists balconies and door frames (Sikaflex AT Connection p.1), or with a general movement-joint sealant (Sikaflex Construction AP p.1). Prime metal railing posts before coating over them (Sikalastic Metal Primer p.1).
Sikaflex AT Connection Sika Request a quotation Sealing joints for: Movement and connection joints, Facade elements, Balconies, Window and door frames, Pre-cast elements, Infill panels. (TDS p.1)
- Temperature stated in TDS
- −40 °C to +70 °C (TDS p.2)
- Pack
- 300 ml cartridges
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 5: Protect, screed and tile
Keep rain off the slurry until it has cured (SikaSeal-105 PK p.2). Lay the protection or bedding screed, then fix tiles with a flexible adhesive rated for outdoor floors (SikaCeram-205 PK p.1).
Product for this stepAsk us The right product here depends on your site. We confirm it before naming it.
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Step 6: Seal movement joints in the tiling
Leave perimeter and bay joints in the tiles and seal them with a floor sealant for pedestrian areas (Sikaflex PRO-3 p.1).
Product for this stepAsk us The right product here depends on your site. We confirm it before naming it.
Proposal brief
Terrace and balcony waterproofing: 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
- Removal of the existing tiles and screed
- Crack sealing and correction of falls
- Two-coat cementitious waterproofing with upstands and threshold detail
- Sealing of wall joints, frames and railing posts
- Screed, tile fixing and movement-joint sealing
System build-up
| Step | Product | Pack | Source |
|---|---|---|---|
| 2. Seal cracks | Sikadur-20 Crack Seal | 160 mL and 850 mL set | TDS p.1 · March 2025, Version 03.02 |
| 3. Apply the waterproofing slurry | SikaSeal-105 PK | — | TDS p.1 · February 2026, Version 02.01 |
| 3. Apply the waterproofing slurry | SikaTop-107 Seal PK | — | TDS p.1 · May 2026, Version 03.02 |
| 4. Seal wall joints, posts and fixings | Sikaflex AT Connection | 300 ml cartridges | TDS p.1 · May 2021, Version 03.01 |
What we need from you
- Balcony or terrace area (m² / sq ft) and wall length
- Photos of the floor, the drain and the ceiling stain below
- Door threshold height compared with the floor
- Tile choice and whether the old tiles may be removed
Site conditions
- Dry weather and shade or cover while the slurry cures (SikaSeal-105 PK p.2)
- Base at least 28 days old before tiling (SikaCeram-205 PK p.2)
- The room below must be accessible for checking
Not included
- Structural repairs to the balcony slab or cantilever, which need an engineer's assessment
- Door, frame or railing replacement
- Supply of client-selected tiles
Questions customers ask
Can the balcony be waterproofed without removing the tiles?
For a balcony people walk on, the waterproofing goes under the tiles, so they have to come up. On a terrace nobody walks on, Sikalastic-510 PK can go over old tiles once their glaze has been removed mechanically (Sikalastic-510 PK p.1, p.2).
How much slurry is needed?
SikaSeal-105 PK uses at least 2.0 kg/m² for damp-proofing, in coats of 1–2 mm (SikaSeal-105 PK p.2).
When can it be painted or covered?
Allow about 5–7 days before painting SikaSeal-105 PK with a compatible decorative coating, depending on thickness (SikaSeal-105 PK p.2).
Water comes in under the door. Is that the balcony?
Ask us: it depends on site conditions. A threshold that sits too low or a failed frame joint can also let water in.
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.