Waterproofing and coating a balcony – step by step
Contents
What you need
Project template “Coat garage and cellar floors”A balcony becomes permanently watertight in three working steps: prime, waterproof with crack bridging, seal. In the Sika balcony system these are Sikafloor-150 as primer (approx. 0.3–0.5 kg/m² per coat), Sikafloor-400 N Elastic as crack-bridging waterproofing (approx. 1.2–1.5 kg/m²) and Sikafloor-410 as transparent PU top sealer (approx. 0.15 kg/m²). The order is decisive: a sealer alone does not waterproof. Anyone who leaves out the crack-bridging layer will have water in the slab again after the first freeze-thaw cycle.
Shopping list
Basic set (always required)
1. Primer
Sikafloor-150 epoxy resin 2K
Penetrates deeply, binds the substrate. Outdoors in two coats, approx. 0.3–0.5 kg/m² per coat.
To the product
2. Waterproofing
Sikafloor-400 N Elastic, 6 kg
Elastic, crack-bridging thin coating. Also adheres to tiles and old coatings. Approx. 1.2–1.5 kg/m².
To the product
3. Sealer
Sikafloor-410 PU, transparent
Protects the waterproofing from UV and abrasion. One-component, straight from the bucket. Approx. 0.15 kg/m².
To the productOptional – depending on the installation situation
- Sikafloor-4005 MTC, 15 l – for larger areas, stairs and access balconies as well as in uncertain weather: thanks to MTC technology, rain-resistant immediately after application.
- Sikaflex-11 FC Purform, 300 ml – for edge and connection joints 10 to 35 mm wide, e.g. at the wall connection or the door threshold.
- Sikafloor-150 binder 2K, 2.5 kg – small container for balconies up to about 4 m².
- Sikafloor-2510, 6 kg – only if the surface is driven on (carport, parking space). Note: this is a sealer, not a waterproofing.
You will find all products of the system in the category Floor coatings & epoxy resin.
Tools
- Electric mixer, infinitely variable speed (the 2K products must be mixed homogeneously)
- Medium-pile, lint-free, solvent-resistant roller for Sikafloor-410
- Short-pile roller or brush for brushing in the first coat of primer
- Trowel or notched squeegee plus deaerating roller for the waterproofing layer
- Moisture or dew point meter, thermometer
- Masking tape, disposable nitrile gloves, safety goggles
Why waterproofing rather than just sealing?
The difference decides the success of the whole project. According to the technical data sheet, Sikafloor-400 N Elastic is a waterproofing, crack-bridging coating for pedestrian surfaces – balconies, terraces, access balconies. It stays elastic and absorbs the movement of the concrete slab instead of cracking through to the surface.
Sikafloor-410, by contrast, is expressly a sealer, not a waterproofing: UV-stable, non-yellowing, approx. 300 % elongation at break (DIN 53455), fire behaviour Cfl-s1 to DIN EN 13501-1. It protects the waterproofing from above but does not replace it. And it is approved for outdoor use only.
The rule of thumb follows from this: if the slab has cracks or there is living space beneath that must stay dry, the crack-bridging waterproofing is mandatory. If the surface is to be driven on by car, the Sika balcony system is the wrong build-up – then the route is via Sikafloor-2510 and our instructions for the garage floor.
Step by step
Check and prepare the substrate
The substrate must be load-bearing, clean and dry and free of greases, oils and separating substances – that is what both data sheets say. Sikafloor-410 states a pull-off strength of over 1.5 N/mm² as a figure; that applies to the whole build-up. Remove old, loose coatings, cement slurry and moss completely, degrease tiles thoroughly.
Why: Every separating layer – even an invisible film of grease from the barbecue – becomes a predetermined breaking point. The waterproofing later tears off there over the whole area, not just at a point.
Check: Film test – stick down a 50 × 50 cm building film tightly and leave for 24 hours. If condensation forms or the concrete turns dark, the slab is too damp. In addition, scratch the surface with the corner of a spatula: if it sands off, more must be removed.
Close edge and connection joints (optional)
Close movement and connection joints at the wall connection, at the door threshold and at the railing base before priming with Sikaflex-11 FC Purform. Approved joint width: 10 to 35 mm, permissible total movement 25 % to ISO 11600, application between +5 and +40 °C. For movement joints, backfill with a closed-cell PE backer rod and avoid air inclusions.
Why: A joint that moves must not be coated over rigidly. The sealant absorbs the movement, the coating runs over it.
Check: Smooth the joint within the skin-over time of around 50 minutes. After 24 hours the sealant has cured about 4 mm deep – test with a fingernail at the edge whether it holds. Important: Sikaflex-11 FC does not adhere to bituminous substrates, EPDM, PE and PP, and is not approved for joints under water pressure.
Prime with Sikafloor-150
Mix both components completely and apply within the pot life. Surfaces directly exposed to the weather – that is, every normal balcony – are, according to the data sheet, primed in two coats, with the first coat brushed in intensively. Consumption per coat approx. 0.3–0.5 kg/m², depending on absorbency. If working in two coats, broadcast with quartz sand of grain size 0.4–0.7 mm.
Why: The primer closes the pores and prevents air from rising out of the concrete into the waterproofing and forming blisters. Broadcasting creates the mechanical key for the layer above.
Check: After drying there must be no matt, absorbent spots left – the surface shines evenly. Broadcast surfaces feel like fine sandpaper. If the quartz sand does not stick, too little material was on the surface.
Waterproof with Sikafloor-400 N Elastic
Mix in the prescribed mixing ratio and apply in several passes as a crack-bridging layer. Consumption on horizontal surfaces approx. 1.2–1.5 kg/m² in total. The material adheres to cement-bound floors as well as to tiles and old coatings – so removing the old tiles is not mandatory.
Why: Crack bridging works only through the layer thickness. Applied too thinly, the layer tears open over the crack, and that is exactly where the water runs in.
Check: Calculate instead of estimating – divide the container contents by the area. A 6 kg container covers around 5 m² at 1.2 kg/m², only 4 m² at 1.5 kg/m². Anyone who manages 8 m² with one container has worked too thinly. Visually, no see-through or grey spots may remain.
Seal with Sikafloor-410
Sikafloor-410 is one-component and is applied evenly straight from the bucket with a medium-pile, lint-free, solvent-resistant roller, approx. 0.15 kg/m² per coat. The climate decides: air and substrate +10 to +30 °C, relative humidity 35 to 80 % (below +20 °C at least 45 %), substrate at least 3 K above the dew point. Working time approx. 60 minutes at +20 °C.
Why: The material cures with atmospheric humidity. Too dry, and it does not cure through; too close to the dew point, and a condensation film forms on which the sealer does not adhere.
Check: The dried surface is evenly satin-matt. Glossy islands mean locally too much material, matt-rough spots too little. Safety: the product is solvent-containing and contains isocyanates – apply only with disposable nitrile gloves and safety goggles, ensure good ventilation, keep away from ignition sources. Heat only with an electric fan heater. Clean tools immediately with Sika Thinner C; cured material can only be removed mechanically.
Leave to cure and release for use
At +20 °C the sealer is rain-resistant after approx. 5 hours and walkable after approx. 8 hours; at +10 °C it takes around 24 hours to become walkable. The surface is fully loadable after approx. 5 days, 4 to 7 days depending on temperature. For the first 24 hours at +20 °C the surface must be protected from dew.
Why: Dew or rain water on the PU layer that has not yet cured through leads to matt patches and a soft, chalking surface – repairable only by sanding off and recoating.
Check: Thumb pressure test at an edge spot. If an impression remains, the surface cannot yet bear loads. Place furniture and planters only after full load capacity.
Material requirement for a 10 m² balcony
| Work step | Consumption | Requirement for 10 m² |
|---|---|---|
| Primer Sikafloor-150 (2 coats) | 0.3–0.5 kg/m² per coat | approx. 6–10 kg |
| Waterproofing Sikafloor-400 N Elastic | 1.2–1.5 kg/m² | approx. 12–15 kg, i.e. 2–3 containers of 6 kg each |
| Sealer Sikafloor-410 | 0.15 kg/m² per coat | approx. 1.5 kg – a 3 l bucket is enough for around 20 m² |
For larger areas the 15 l container Sikafloor-4005 pays off. For other waterproofing tasks, our waterproofing calculator helps with working out quantities.
Waiting times and checks
| After this step | Wait | Check before continuing |
|---|---|---|
| Substrate prepared | film test 24 h | No condensation under the film, no sanding off when scratched |
| Edge joint with Sikaflex-11 FC | approx. 24 h (approx. 4 mm through-curing) | Joint edge withstands fingernail pressure; smoothing within approx. 50 min done |
| Primer Sikafloor-150 | waiting time per technical data sheet, short according to the manufacturer | No matt absorbent spots; quartz sand sits firmly |
| Waterproofing Sikafloor-400 N | intermediate and overcoating times per technical data sheet | Consumption per m² recalculated; no see-through spots |
| Sealer Sikafloor-410 | rain-resistant approx. 5 h, walkable approx. 8 h (+20 °C) or approx. 24 h (+10 °C) | Evenly satin-matt, no thumb impression |
| Surface finished | fully loadable approx. 5 days (4–7 days depending on temperature) | Only then place furniture, planters and point loads |
Mixing ratios, pot lives and overcoating intervals of the 2K products are in the respective Sika technical data sheet – these figures are temperature-dependent and take precedence.
Common mistakes – and how to avoid them
- Only sealing instead of waterproofing. The most common and most expensive mistake. Sikafloor-410 is expressly not a waterproofing; without Sikafloor-400 N the slab remains open to water.
- Applied too thinly. Crack bridging comes about through layer thickness. Always check via the consumption per m², not by visual impression.
- Primed only once. Outdoors the data sheet prescribes two coats, the first brushed in intensively. One coat is not enough on absorbent concrete.
- Worked on the wrong day. Below +10 °C, above 80 % humidity or less than 3 K above the dew point there is no usable sealing. In spring and autumn the surface quickly falls below the dew point in the evening – start in the morning.
- Coated a driven-on surface with the balcony system. Sikafloor-400 N Elastic is approved only for pedestrian surfaces. For garage, carport and parking space, Sikafloor-2510 is the right product.
- Forgot slip resistance. The tested slip resistance R9 to R11 to DIN 51130 comes from the Sikafloor anti-slip additive in the sealer, not from loose quartz sand. Without the additive, the sealed surface stays slippery when wet.
Matching guides
- Instructions: coating a garage floor with epoxy resin – for driven-on surfaces
- Instructions: sealing joints with Sikaflex 11 FC – details on the edge and connection joint
- Guide: Waterproofing slurry or bitumen – what goes where? – waterproofing on components in contact with the ground
- Waterproofing calculator – quantities for waterproofing slurry and liquid membrane
Frequently asked questions
Can I coat directly onto old tiles?
Yes. According to the product data, Sikafloor-400 N Elastic adheres to cement-bound floors as well as to tiles and old coatings. Prerequisite: the tiles are firmly bonded, thoroughly degreased and the substrate is suitably primed. Remove tiles that sound hollow beforehand and reprofile the spot.
How much material do I need for my balcony?
Per square metre, allow 0.3–0.5 kg of primer per coat (outdoors two coats), 1.2–1.5 kg of Sikafloor-400 N Elastic and 0.15 kg of Sikafloor-410. For 10 m² that is about 6–10 kg of primer, 12–15 kg of waterproofing and 1.5 kg of sealer.
When may I step onto the balcony again?
At +20 °C, Sikafloor-410 is rain-resistant after approx. 5 hours and walkable after approx. 8 hours. At +10 °C that extends to around 24 hours. The surface is fully loadable – that is, ready for furniture and planters – after about 5 days, after 4 to 7 days depending on temperature.
May I use the system in the garage or indoors?
No. Sikafloor-410 is approved by Sika exclusively for outdoor use, not for interiors. And Sikafloor-400 N Elastic is intended only for pedestrian surfaces – for driven-on surfaces such as garage, carport or parking space, Sikafloor-2510 is the suitable product.
What if it might rain during the work?
Then Sikafloor-4005 is the safer choice: thanks to MTC technology this balcony waterproofing is rain-resistant immediately after application. With Sikafloor-410, on the other hand, you must allow for around 5 hours of rain resistance and protection from dew during the first 24 hours.
Do I need training for the products as a business?
For Sikafloor-410 yes: it contains isocyanates, commercial users have needed training under REACH Annex XVII No. 74 since 24 August 2023. According to the data sheet, Sika in any case approves the product only for commercial applicators. Sikaflex-11 FC Purform is exempt, because the content of free monomeric diisocyanates is below 0.1 %.
Questions about the build-up? Give us a call: Baustoffheld, Lindenstrasse 56, 47623 Kevelaer, +49 (0) 2831 - 916 77 03.
Basic set: the products you always need
3 variants
Content: 2,5 Kilogram (€39.12 / 1 Kilogram)
Content: 6 Kilogram (€41.66 / 1 Kilogram)
2 variants
Content: 3 Litre (€63.32 / 1 Litre)
Optional – depending on the installation
Content: 13,5 Kilogram (€35.18 / 1 Kilogram)
3 variants
Content: 0,3 Litre (€29.97 / 1 Litre)
7 variants
Content: 6 Kilogram (€34.99 / 1 Kilogram)
Content: 2,5 Kilogram (€30.48 / 1 Kilogram)
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