⚠️ Safety note: Interior waterproofing (bathrooms, kitchens, floors) is fairly forgiving — following the product instructions and basic sequence is usually fine. Facades, rooftops, large-area or structural waterproofing are high-risk: material selection and workmanship are more demanding and depend on drainage, substrate condition and how the area is used. Consult relevant professionals. This article is general selection guidance only; the actual method depends on site conditions and the product technical data sheet (TDS).
Where does a home leak most often?
Hong Kong is subtropical, and spring–summer humidity often reaches around 90%, so mouldy walls, blistering floors and leaks are common. Left untreated, they don't just look bad — they damage the structure and the neighbours below, and cause disputes. The spots that most often fail: bathrooms and kitchens (constant water), window sills and external walls (rain exposure), and rooftops and terraces (large, sun- and rain-exposed areas). Different spots need different materials — there's no "universal" waterproofing.
How are waterproofing materials classified?
1. Flexible cementitious waterproofing — bathroom, kitchen, water-tank base waterproofing
A two-component cement-based coating that forms an elastic, water-blocking layer able to resist minor cracks. It's the most common base waterproofing for interior wet areas (bathrooms, kitchens, terraces, water tanks, reservoirs), and you can tile over it afterwards. Elasticity is limited, so it's not for joints with large structural movement, and most types aren't UV-resistant, so not for long-term sun exposure.
Common examples: Sika Top Seal 107, Fosroc Brushbond FLXIII. → Browse the flexible cementitious range
2. Bonding agent / SBR latex — better adhesion and mortar waterproofing
A latex additive mixed into cement mortar or brushed on as a bonding coat: it improves adhesion between old and new materials, reduces delamination, and improves the mortar's water resistance and crack resistance. Often used before waterproofing renders, plastering or skim coats.
Common examples: SikaLatex, Ronafix. → Browse the bonding agent / SBR latex range
3. Movement-joint / joint sealant — joints, window frames, expansion joints
A single-component elastic sealant (silicone / glass glue, or polyurethane) for sealing moving junctions between different materials — window frame to wall, expansion joints. Note it seals a "line", not a whole surface like a coating.
Common examples: Dowsil 791 weatherproofing sealant, Sikaflex Construction. For neutral vs acetoxy and the 791/793/795 differences, see the glass-glue guide below. → Browse the sealant / glass glue range
4. Penetrating water repellent — external walls, fair-faced concrete
A penetrating repellent soaks into the substrate's pores so the surface repels water without trapping water vapour — good for external walls and fair-faced concrete where you don't want to change the appearance. It's a surface water-repellent treatment, not the same as building a waterproofing membrane.
Example: Sikagard 705 L penetrating water repellent.
5. Tile grout — tile joints
Used to fill the joints between tiles; easy to apply. But its water resistance is limited — it's not a waterproofing layer and won't take long-term immersion. Leaks at tile joints usually need the base waterproofing checked too.
What about rooftops, external walls and large areas?
Rooftops, terraces and basements — large-area or exposed waterproofing — are specialist waterproofing systems. The types and workmanship are far more involved than interior work, and they depend on drainage, substrate condition and future use. This work relies heavily on site judgement, and choosing the wrong material or method carries real risk, so we recommend consulting a professional for your specific situation rather than relying on a single article. Feel free to WhatsApp us to discuss the site conditions first.
What to consider when choosing waterproofing materials
- Location — interior wet areas, joints, external walls and large areas each have their own materials; identify the spot first.
- Substrate — concrete, render, tiled surface or metal; whether a material suits depends on the substrate.
- Weathering — exposed sunlit areas need UV resistance; interior matters less.
- Workmanship — some need a professional team, some a tradesperson can handle.
- Supply and support — choose reputable brands and suppliers for easier re-ordering and technical support.
Common waterproofing mistakes
- Poor substrate prep — oil, dust and loose material stop the layer bonding; clean and dry the substrate before applying.
- Coating too thin — insufficient thickness is the most common failure; apply to the recommended thickness on the product sheet.
- Missing internal corners and pipe penetrations — wall corners, floor drains and pipe penetrations leak most; reinforce these spots.
- Insufficient curing — tiling or covering before the layer fully cures ruins the waterproofing; a water (ponding) test is usually run for a day or more.
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FAQ
Which material should I use for home waterproofing in Hong Kong?
It depends on the spot: for base waterproofing of interior wet areas (bathrooms, kitchens, terraces), flexible cementitious waterproofing is most common; for joints and window frames, a sealant; for tile joints, tile grout; for external fair-faced concrete, a penetrating water repellent. No single material does everything — identify the location first.
What's the difference between flexible cementitious waterproofing and SBR latex (bonding agent)?
Flexible cementitious waterproofing is a coating that blocks water on its own; SBR latex / bonding agent is an additive that improves adhesion and the mortar, and is not the main waterproofing layer itself. The two are often used together — see the "flexible cement vs SBR" article.
How thick should the waterproof coating be?
Thickness directly affects performance, and too thin is the most common failure. The actual recommended thickness, number of coats and drying time between coats should follow that product's technical data sheet (TDS) — it varies by product.
When can I tile after waterproofing?
Wait until the waterproofing layer has fully cured before tiling; covering it too early ruins the waterproofing. Actual curing time depends on product, thickness, temperature and humidity — follow the TDS; a water test is usually run first to confirm there are no leaks.
Glass glue or tile grout for a leaking tile joint?
Joints between tiles use tile grout; glass glue (sealant) seals moving junctions between different materials. They serve different purposes. A persistent leak usually needs the base waterproofing checked too, not just re-pointing the joint.
How do I waterproof a rooftop?
A rooftop is large-area, exposed waterproofing — the material types and workmanship are more involved, and depend on drainage and substrate condition, so it relies heavily on site judgement. We recommend consulting a professional for your specific situation rather than relying on general information to choose materials yourself.
