Video by Skill Builder. This guide draws on the practical demonstration "How to Apply Cempolatex Self Levelling Screed" from Skill Builder, Roger Bisby’s well-respected UK trade and DIY channel. Roger explains the proper use of latex-modified self-levelling compound in a clear, no-nonsense way — the section on priming and water ratios is particularly worth watching before you mix your first bag.
1. Check the subfloor condition
Self-levelling compound will not fix a floor that is structurally unsound. Walk every square metre and listen for movement. Any loose boards need to be screwed down; any hollow tiles need to come up. The compound flows to fill voids, but only if those voids are not going to shift again once it cures.
Sweep the floor thoroughly. Any grit, dust, or debris will bond into the compound surface and create high spots. This is also the moment to check for any oil or grease contamination — particularly in kitchens or garages — and degrease if needed.
2. Seal gaps and edges
Self-levelling compound is liquid. It will find every gap and vanish down it if you let it. Seal around pipes, between boards, and along skirting boards with flexible adhesive or expanding foam. Mind you, even small gaps you think are insignificant can drain a whole bucket in seconds.
Use a temporary dam of foam backer rod or duct tape at any doorways if you are only doing one room. You want the compound to settle flat within the area you are working, not spread into the hallway.
3. Prime the subfloor
This is the step most people skip and then wonder why the compound curls at the edges or peels away. Priming is not optional. Apply a diluted PVA solution or a dedicated floor primer with a brush or roller, and allow it to become tacky — not wet, not bone dry. The timing matters.
Concrete floors need primer too. Absorbent concrete will suck the water out of the compound too quickly, leaving a weak, crumbly surface. A couple of coats of primer sorts that out.
4. Mix the compound correctly
Read the bag. That is not something people often say and mean, but the water ratio for self-levelling compound is genuinely critical. Too much water and it flows beautifully but dries weak and chalky. Too little and it goes lumpy, sets too fast, and will not level itself at all.
Add the powder to the water, not the other way round. Use a paddle mixer in a drill at medium speed. Mix for two full minutes, scraping the sides, until you have a smooth lump-free slurry. Work quickly — most compounds have a pot life of around ten to fifteen minutes.
5. Pour and spread
Start in the corner furthest from the door and pour steadily, moving back as you go. The compound will spread itself, but give it a hand with a gauge rake or a long squeegee to guide it into corners and under obstacles.
Work fast. The moment the surface starts to skin, stop spreading — dragging a tool over skinning compound tears it rather than smoothing it. If you need more depth than one pour, check the manufacturer’s maximum per pour and plan accordingly.
6. Pop any bubbles
Pass a spiked roller over the wet compound to release any trapped air. Bubbles left to cure will leave small pits in the surface, which can telegraph through thin floor finishes.
That said, do not overwork the surface. A couple of passes with the spiked roller is enough. You are not trying to spread it further at this point — just releasing air.
7. Allow to cure fully before laying the floor
Drying time and curing time are different things. The surface may be walk-on dry within an hour, but the compound needs significantly longer to reach full strength. Check the bag for the minimum wait before laying tiles, LVT, or laminate — typically 24 hours, sometimes longer for thicker pours.
Keep windows closed and avoid temperature swings during curing. Draughts can cause the surface to dry unevenly, leaving a powdery top layer that floors will not bond to properly.
When to call a handyman
Call Richard if the floor drops more than 10mm over a short span, if there are structural issues underneath, or if you are working over electric underfloor heating where cutting into the screed carries a risk of damage. Large commercial areas also benefit from a professional pour, where multiple bags need to be mixed and placed in sequence without cold joints forming.
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