Summary (TL;DR)
Self-levelling is a highly fluid cement-based floor levelling material that flows and levels itself when poured — a different approach from the traditional method of hand-laying and trowelling sand-cement screed, and each suits different jobs. In recent years, floating / click-lock floors such as SPC stone-plastic flooring, vinyl flooring and engineered wood flooring have become popular in renovations; these demand a very flat base, so laying a self-levelling underlayment beforehand has become key to the flooring's lifespan. Hong Kong is humid, so cement-based is the mainstream choice. Applying a primer before installation strengthens adhesion and reduces the risk of delamination and blistering; on older or more absorbent substrates (such as old-building floors), a primer is strongly recommended.
What Is Self-Levelling? How Does It Differ from Traditional Hand Levelling?
Traditional floor levelling has the mason lay sand-cement (cement plus sand) on the floor and trowel it flat by hand (commonly called "screeding" or "rendering" the floor). This method is time-tested and reliable, and is especially suited to large-area build-ups and thick levelling; how flat it turns out depends on the tradesperson's skill and experience, and it is relatively more labour- and time-intensive.
Self-levelling takes another route: once mixed with water it becomes a fluid slurry that, when poured, flows outward and levels itself; you just spread it lightly and roll out the air bubbles. Neither replaces the other — each has its strengths. Self-levelling's main features are:
- Flatness is easy to achieve — the material levels itself, with less dependence on hand skill
- High efficiency — pour a large area in one go, quick to apply
- Smoother surface — especially suited to jobs where thin flooring is laid on top
- Can achieve a very thin levelling layer — sand-cement needs a certain thickness to lay stably; thin-layer levelling is exactly self-levelling's strength, staying smooth and solid even in a thin coat
On cost, self-levelling material usually has a higher unit price than sand-cement, but it wins on speed of application, easy flatness control and the ability to go thin; for large build-ups, thick layers or budget-driven jobs, traditional sand-cement still has its place. Which to choose ultimately depends on the actual needs of the job.
Why does "going thin" matter when changing flooring? When you change a flooring system, the room you have to raise the floor is often limited. The thicker the base build-up, the more likely the new floor will hit the door once laid — needing the door planed or trimmed shorter — or create a floor-height difference between rooms that needs a transition strip. Sand-cement needs a certain thickness and will raise the floor accordingly; if height is tight on site, self-levelling can do a thin levelling layer that keeps the added height to a minimum — especially practical for older-building renovations switching to SPC or wood flooring.
Why Has Self-Levelling Become Popular Lately? (Especially Before SPC / Wood Flooring)
In recent years Hong Kong renovations often use SPC stone-plastic flooring, vinyl flooring and engineered wood flooring — these floating (glue-free, click-lock) floors. Such floors are thin and hard, "float" above the base and connect via click-locks rather than bonding to the floor. Precisely because of this, they demand a very flat base.
If the base is uneven with large deviations, after laying you easily get:
- "Clicking" sounds and a springy feel underfoot — gaps between the floor and the base
- Click-locks cracking under load — over time the locks at uneven spots crack
- Seams opening and lifting — planks push apart and, over time, deform
So before laying this type of floor, doing a flat, smooth self-levelling base first is like building a good foundation for the floor, greatly reducing future noise and lifting. This is also the main reason demand for self-levelling has surged recently.
Types of Self-Levelling — Know These Before You Choose
There are many kinds of "self-levelling" on the market, and using the wrong type can mean wasted work. Before buying, at least sort out the following three distinctions.
Cement-based vs Gypsum-based
Cement-based self-levelling uses cement as the base, is moisture-tolerant and widely applicable — the mainstream choice in the Hong Kong market. Gypsum-based self-levelling flows well but fears water and damp — in humid Hong Kong, especially during the "return-south" damp season, it easily fails on contact with substrate moisture or seepage, so it is generally not recommended for floors, kitchens/bathrooms or below-grade levels. In short: in Hong Kong, cement-based is basically the safe default.
Underlayment (Base) vs Overlayment (Top)
Underlayment type is a levelling layer laid beneath another finish (e.g. flooring, carpet, resin surface) and is not the final walking surface itself. Overlayment type has higher hardness and abrasion resistance and can, in part, serve as the final floor directly (some still need a protective coating). Check the product's positioning before buying — don't use an underlayment type as an overlayment.
Indoor vs Outdoor
This article focuses on indoor use. For outdoor areas or places exposed to prolonged sun and rain, choose a dedicated weather-resistant grade — don't casually take an indoor type outside.
| Type | Characteristics | Common HK use |
|---|---|---|
| Cement-based | Moisture-tolerant, widely applicable | Mainstream, suits almost all indoor floors |
| Gypsum-based | Flows well but fears damp | Humid HK, generally not recommended |
| Underlayment | Levelling layer beneath a finish | Base before SPC / wood flooring |
| Overlayment | Higher hardness & abrasion resistance | Can be the final floor (some need a protective coat) |
How to Choose Thickness?
Self-levelling is not "the thicker the better" — every grade has a recommended application thickness range. If you just want a thin skim to level and smooth the surface, choose a thin-layer type; if the floor has larger deviations to fill, choose a type that can go thicker. Avoid pouring a thin-layer type very thick in one go — it cracks easily. For the actual recommended thickness, coverage and curing time, follow the product Technical Data Sheet (TDS).
General principle:
- Thin layer, fast-drying, base before thin flooring — consider GOTECH GT 818 Self-Levelling Floor Screed
- Larger deviations, more versatility or higher strength — consider Sika Sikafloor 357 Level Self-Levelling
If you want to directly compare the thin-base vs thick-levelling options across grades, see the full range: Self-Levelling product range.
Primer (Bonding Agent): What It Does & When to Use It
Primer (some call it a bonding agent) is a base coat brushed onto the substrate and left to dry before pouring self-levelling. Brushing on a primer before the self-levelling has some very practical benefits:
- Seals substrate pores — prevents the base from "drinking away" the self-levelling's water, so it doesn't dry too fast and crack
- Prevents blistering — air rising from substrate pores can cause surface blisters and pinholes
- Increases adhesion — bonds the self-levelling firmly to the base, reducing later delamination/peeling
When is it most worth doing? The poorer the substrate condition, the more worthwhile it is: the older, dustier or more absorbent the substrate (e.g. old-building floors, rendered surfaces), the more a primer is recommended to strengthen adhesion and reduce delamination and blistering. On highly absorbent substrates, it also helps to dampen the surface with water beforehand so the self-levelling doesn't dry too fast.
In short, a primer helps the self-levelling bond more firmly and last longer; the poorer the substrate condition, the more worthwhile the extra step. For a compatible primer, see Optimix SF80 Bonding Primer.
Three Common Self-Levelling Failures: Delamination, Dusting, Cracking
Whether self-levelling turns out well often comes down not to the material but to the details. The following three are the most common failures in Hong Kong:
1. Delamination / Debonding (layer separation)
The self-levelling layer separates from the base — it sounds hollow when tapped and can even peel off. The most common cause is dust or grease not cleaned off the substrate, giving a weak bond; an overly dry, overly absorbent substrate makes it worse. Fix: thoroughly clean and grind the substrate; if it's highly absorbent, dampen it beforehand or brush on primer to strengthen the bond.
2. Dusting / Powdering
The surface rubs off into sand/powder and isn't hard enough. The most common cause is adding too much water when mixing (over-watering to improve flow), which drops the strength sharply. Fix: strictly follow the product's specified water quantity — 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, and don't force a thin-layer type to fill thick spots.
Application Steps & Tools (Simplified)
Self-levelling looks simple, but there are basic steps you can't skip. Below is a simplified flow (follow the product TDS for the actual process):
- Clean and grind the substrate — remove dust, grease and loose material
- Fill large holes, seal edges — fill big depressions first; seal doorways and pipe penetrations against slurry leaks
- Apply primer — dilute per instructions, wait until touch-dry (per TDS)
- Mix with water — use an electric mixer, mix to a lump-free slurry at the specified water quantity
- Pour and spread — spread evenly with a spreader / self-levelling rake
- Remove air bubbles — step in with spiked shoes and roll out bubbles with a spiked (de-airing) roller
- Cure and dry — cure per the TDS time; lay flooring only once fully dry enough for the top layer
Common tools: electric mixer, spreader / self-levelling rake, spiked (de-airing) roller, spiked shoes, bucket, floor primer, leak-proof edge sealing tape.
FAQ
How do I choose self-levelling thickness?
It depends on the floor's deviation and the grade. For a thin skim to level, choose a thin-layer type; for larger deviations to fill, choose a type that can go thicker. Avoid pouring a thin-layer type thick in one go; for the actual recommended thickness, refer to the product Technical Data Sheet (TDS).
When should I use a primer (bonding agent) for self-levelling?
Brushing on a primer seals substrate pores and strengthens adhesion, reducing delamination and blistering. The older, dustier or more absorbent the substrate (e.g. old-building floors), the more it is recommended to prime first. On highly absorbent substrates, dampening the surface with water beforehand also helps.
Is gypsum-based self-levelling suitable in Hong Kong?
Hong Kong is humid, especially in the damp return-south season; gypsum-based fears water and damp, so it is generally not recommended for floors, kitchens/bathrooms or below-grade levels. Cement-based self-levelling is the more robust mainstream choice in Hong Kong.
Must I do self-levelling before laying SPC or wood flooring?
Floating / click-lock floors demand a flat base; an uneven base easily causes clicking sounds, cracked locks or opened seams. If the original floor has obvious deviations, it is advisable to level it with self-levelling first.
What is the difference between self-levelling and traditional sand-cement screeding?
Traditional sand-cement is hand-laid and trowelled flat by the tradesperson, suited to large build-ups and thick levelling, with flatness depending on their skill; self-levelling flows and levels itself — thin, fast, easy flatness control — especially suited as a base before thin flooring. Each has its place.
Where can I buy self-levelling?
Wah Hing stocks self-levelling compounds and compatible primers from several brands, with most products typically in stock. Visit our Canton Road store to enquire, or use the WhatsApp button on the site to ask about stock.
Ready to buy? Wah Hing stocks the self-levelling range, compatible primers and installation accessories, with most products typically in stock — visit our Canton Road store or WhatsApp us.
