Overview (TL;DR)
Self-levelling is a high-flow cement-based floor levelling material — mixed with water and poured, it spreads and levels itself into a smooth, flat surface, and has its place alongside the traditional hand-applied sand-cement screed. This is the overview guide to self-levelling: material types (cement- vs gypsum-based, underlayment vs overlayment, indoor vs outdoor), thickness, primer, common failures and installation in one place. To go deep on base-layer prep before laying floor coverings, also read our underlayment (base-layer) guide for laying floor coverings.
What is self-levelling? How is it different from hand-applied levelling?
Traditional floor levelling has the tradesperson lay sand-cement and trowel it flat by hand. It's a long-proven method, especially for large-area build-ups and thick levelling, with flatness depending on the tradesperson's skill. Self-levelling takes another route: once mixed it's a flowable slurry that spreads and levels itself, needing only light spreading and de-airing. Neither replaces the other — each has its strengths. Self-levelling wins on easy-to-control flatness, speed, a smooth finish and the ability to go as a thin layer; for large build-ups, thick levelling or budget-led jobs, traditional sand-cement still has its place. Which to use comes down to the job.
Three floor-levelling methods compared
There are actually more than two ways to level a floor before flooring — between "site-mixed sand-cement" and "self-levelling" sits a third option: pre-blended floor screed (bagged, just-add-water levelling screed). Each has its place:
| Comparison | Site-mixed sand-cement | Pre-blended floor screed | Self-levelling |
|---|---|---|---|
| Method | Hand-troweled and floated | Bagged, add water, hand-troweled | Add water, pour, self-levels |
| Thickness / level difference | Thick, large build-ups | Medium-to-thick levelling | Thin-to-medium smoothing |
| Surface smoothness | Depends on the tradesperson | Flat (not always glass-smooth) | Smoothest, ready for thin coverings |
| Set / dry speed | Slower | Fast-drying | Fast-drying, fast to apply |
| Shrinkage / cracking risk | Higher (depends on mix) | Lower (anti-shrinkage formula) | Low (thin, low-shrinkage) |
| Consistency / control | Most dependent on site materials and skill; quality and time vary most | Factory pre-blended, more consistent | Mostly poured, flatness easier to control |
| Cost tendency | Lowest material cost, but most labour and time | Moderate material cost — the balanced option | Higher material cost, wins on speed and smoothness |
| Best fit | Large build-ups, big drops in old buildings | Medium/thick levelling, needing consistent quality or waterproofing (some grades) | A smooth base before SPC/vinyl, thin smoothing |
The three actually combine — it is not either/or. For example, where an old floor has a big drop, build up most of it with site-mix or pre-blended screed, then finish with a thin, smooth self-levelling layer — each doing its job. The pre-blended floor screed is the balanced middle ground: more consistent than site-mixing, fast-drying, and some grades are waterproof — e.g. Optimix FS161 waterproofing floor screed, Weberfloor Easi Screed, Weberdry WP Screed. See the full range in our floor screed collection.
What is self-levelling used for? (Common Hong Kong scenarios)
Self-levelling is more versatile than people think — not just base prep before flooring. Here are common HK scenarios:
- Base prep before floor coverings — a flat base for SPC, vinyl, wood flooring and tiles; the most common approach in public/HOS flat overhauls laying SPC (see our underlayment (base-layer) guide for laying floor coverings)
- Old-building / walk-up floor renovation — old floors have big level differences and are prone to spring damp; thick-fill grades correct the levels, and damp substrates are best primed with a damp-proof primer first
- Office / commercial floors — base prep before carpet tiles, sheet vinyl or raised access floors; the key is fast-drying, overnight turnaround that doesn't disrupt business
- Industrial-building / studio decorative cement floors — studios in areas like Kwun Tong and Lai Chi Kok love the raw "cement look" and use an overlayment grade as an exposed decorative floor; mix thoroughly and add a sealer (e.g. clear epoxy) or you risk patchy colour and visible trowel marks
- Coloured & decorative floors — some overlayment grades can be left exposed as the final floor, in coloured, polished or terrazzo effects
- F&B / shops (hygiene-sensitive) — high foot traffic plus FEHD hygiene requirements; some grades are free from casein/protein additives, suiting kitchen and food-processing floors
- Exterior floors — exterior grades with waterproofing additives suit open walkways, courts, playgrounds and occasionally-wet areas
- Modular construction (MiC / DfMA) — some grades suit modular components and pre-assembled floors, giving a fast, flat levelling base
How are self-levelling types divided? Sort this out before buying
There are many kinds of "self-levelling" on the market, and using the wrong type can waste the whole job. At minimum, sort out the groups below before buying.
Cement-based vs gypsum-based
Cement-based self-levelling uses cement as the binder — moisture-tolerant, versatile, and the mainstream choice in Hong Kong. Gypsum-based self-levelling flows well but is moisture-sensitive — in humid HK, especially 回南天, it easily fails on damp or seeping substrates, so it is generally not advised for floors, kitchens/bathrooms or below-grade areas.
Underlayment (base) vs overlayment (top)
Underlayment type is a levelling layer laid beneath a finish (flooring, carpet, resin surface) and is not the final walking surface. Overlayment type has higher hardness and abrasion resistance; some can serve as the final floor directly (some still need a protective coating), and can even form coloured, polished or terrazzo-effect decorative floors.
Underlayment examples: Optimix SF818 (standard interior base), Weberfloor 230 (thick base). Overlayment examples: Optimix SF878 (heavy-duty), Optimix SF838 (coloured decorative), Mapei Ultratop (can be left exposed as the final floor).
Indoor vs outdoor
Most self-levelling is for interior use. For outdoor areas or spots exposed to prolonged sun and rain, choose a dedicated weather-resistant grade — don't casually take an indoor grade outside. Wah Hing carries exterior-grade options such as Optimix SF868 exterior topping (with waterproofing additives, for open walkways, courts, playgrounds and occasionally-wet areas).
| Type | Characteristics | Common HK use |
|---|---|---|
| Cement-based | Moisture-tolerant, versatile | Mainstream, for most interior floors |
| Gypsum-based | Flows well but moisture-shy | Humid HK — generally not advised |
| Underlayment | Levelling layer below a finish | Base prep before floor coverings |
| Overlayment | Harder/abrasion-resistant, some exposed | Final floor, coloured or decorative |
| Exterior | Waterproofing additives, weatherproof | Open walkways, courts, playgrounds |
How to choose thickness?
Self-levelling is not "thicker is better" — each grade has a recommended thickness range. For a thin smoothing layer, choose a thin-layer grade; for larger level differences, choose one that can be built up thicker. Never pour a thin-layer grade too thick in one pass — it cracks easily. For actual thickness, coverage and curing time, follow the product Technical Data Sheet (TDS).
- Thin, fast-drying, base before thin floor coverings — consider GOTECH GT 818 self-levelling
- Larger level differences, broader use — consider Sika Sikafloor 357 Level
To see the full range and primers, visit our self-levelling range.
Primer (bonding agent): what it does, and when to use it
Primer (also called bonding agent) is a coat brushed onto the substrate and left to dry before pouring self-levelling. Applying it is practical:
- Seals substrate pores — stops the substrate "drinking" the water out of the self-levelling and drying it too fast (which causes cracking)
- Prevents bubbling — outgassing from substrate pores causes surface bubbles and pinholes
- Boosts bond — helps the self-levelling grip the substrate, reducing later delamination
When is it most worth it? The older, dustier or more absorbent the substrate (e.g. old flats, rendered surfaces), the more it's recommended to prime first, to strengthen the bond and reduce delamination and bubbling. Very absorbent substrates can also be dampened with water before pouring. Matching primers include Optimix SF80, Weberfloor Primer and Mapei Primer SN.
The three common self-levelling failures: delamination, dusting, cracking
Whether self-levelling turns out well often comes down to details, not the material. These three are the most common failures in Hong Kong:
1. Delamination / hollowness
The self-levelling separates from the substrate — press it and it sounds hollow, or it lifts. The most common cause is dust or grease not cleaned off the substrate, so the bond is weak; a too-dry, too-absorbent substrate makes it worse. Fix: thoroughly clean and abrade the substrate; dampen very absorbent substrates first, or prime to boost bond.
2. Dusting / powdering
The surface rubs off as sand or powder and isn't hard enough. The most common cause is too much water in the mix, which drops the strength. Fix: strictly follow the product's specified water dosage — don't add extra.
3. Cracking
Cracks appear on the surface. Common causes are pouring too thick in one go (exceeding the grade's recommended thickness), active cracks in the substrate itself, or not handling movement joints. Fix: apply in layers per the grade's thickness, keep existing structural and movement joints; if the substrate is old or prone to cracking, you can also choose a fibre-reinforced grade to help resist cracking.
Installation steps and tools (simplified)
Self-levelling looks simple but has basic steps you can't skip. Here's a simplified flow (follow the product TDS for the actual method):
- Clean and abrade the substrate — remove dust, grease and loose material
- Patch big holes, seal edges — fill large dips first; seal doorways and pipe penetrations against slurry leaks
- Apply primer — dilute per instructions, wait until touch-dry (per TDS)
- Add water and mix — use a power mixer, mix to the specified water dosage until lump-free
- Pour and spread — lightly spread even with a spreader / self-levelling rake
- De-air — walk in with spiked shoes and roll out air bubbles with a spiked roller
- Cure and dry — cure per the TDS time; only lay the finish once fully dry
Common tools: power mixer, spreader / self-levelling rake, spiked de-airing roller, spiked shoes, buckets, floor primer, edge-sealing tape.
Product recommendations (by use)
Not sure which to pick? Use the pairings below; follow each product's TDS for grade, thickness and curing time.
Thin base (before thin floor coverings)
GOTECH GT 818 self-levelling — thin, fast-drying, for base prep before SPC, vinyl and other thin coverings.
General interior levelling (replaces sand-cement screed)
Optimix SF818, Weberfloor 550, Mapei Novoplan DA — mix with water and self-level, replacing hand-troweled screed, flat and fast.
Thick fill, larger level differences
Optimix SF806, Weberfloor 230, Sika Sikafloor 357 Level — thick single-pass levelling to correct larger differences.
Coloured / decorative overlayment
Optimix SF838, Weberfloor 810 coloured self-levelling, Mapei Ultratop — can be left exposed as the final floor; some allow polished or terrazzo effects.
Heavy-duty wearing overlayment
Optimix SF878, Weberfloor 860 — abrasion-resistant, high strength, for higher-traffic industrial and commercial floors.
Exterior overlayment
Optimix SF868 exterior topping — with waterproofing additives, for open walkways, courts, playgrounds and other outdoor spots.
Matching primer (bonding agent)
Optimix SF80, Weberfloor Primer, Mapei Primer SN — especially recommended on older or absorbent substrates.
To see the full range, visit our self-levelling range.
FAQ
What's the difference between cement-based and gypsum-based self-levelling? Which should Hong Kong use?
Cement-based self-levelling is moisture-tolerant and versatile — the mainstream choice in Hong Kong. Gypsum-based flows well but is moisture-sensitive, so it is generally not advised for floors, kitchens/bathrooms or below-grade areas. In humid HK, especially the 回南天 condensation season, cement-based is the safe default.
How do I tell an underlayment grade from an overlayment grade?
Underlayment sits below another finish as a levelling layer — not the final walking surface. Overlayment has higher hardness and abrasion resistance; some can serve as the final floor, and certain products can be finished as coloured or terrazzo effects. Check the product's positioning before buying — don't use an underlayment as an overlayment.
Is self-levelling indoor-only? Can it go outdoors?
Most grades are for interior use, but there are dedicated exterior grades (with waterproofing additives, for open walkways, courts, playgrounds and occasionally-wet areas). For outdoor or sun/rain-exposed spots you must use a proper exterior/weather-resistant grade — never take an indoor grade outside.
How do I choose the thickness?
Every grade has a recommended thickness range. For a thin smoothing layer choose a thin-layer grade; for larger level differences choose a grade that can be built up thicker. Never pour a thin-layer grade too thick in one pass — it cracks easily. Follow the product Technical Data Sheet (TDS) for actual thickness.
When do I need primer (bonding agent)?
Primer seals the substrate's pores, boosts bond, and reduces delamination and bubbling. The older, dustier or more absorbent the substrate (e.g. old flats, rendered surfaces), the more it is recommended to prime first. Very absorbent substrates can also be dampened with water before pouring.
Can self-levelling create decorative floors or a terrazzo effect?
Yes. Some decorative overlayment grades can form coloured floors, and certain products can achieve a polished or terrazzo effect — ideal for showrooms, shops and other appearance-conscious floors.
Where can I buy self-levelling compound?
Wah Hing stocks self-levelling and matching primers from several brands, most typically in stock. Visit our Canton Road shop in Mong Kok, or contact us via WhatsApp.
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Ready to buy? Wah Hing stocks the self-levelling range, matching primers and installation accessories, most typically in stock — visit our Canton Road shop in Mong Kok or ask us on WhatsApp.
