How to Level a Floor Before Tiling or Laying LVT
Most flooring failures are not the fault of the flooring. Tiles that crack in a line, vinyl planks that lift at the edges, laminate that clicks and rocks underfoot: nine times out of ten the problem is underneath, in a subfloor that was never flat enough to begin with. Getting that base right is the least visible part of any flooring job and the part that decides whether it lasts.
Start by finding out how bad it is. Lay a long straightedge, a two-metre level or a straight timber batten across the floor in several directions and look for gaps underneath. Anything more than about 3mm under a two-metre span is worth sorting before you lay a finished floor, and for large-format tiles or vinyl the tolerance is tighter still, because those materials telegraph every dip and hump.
Small, local dips can sometimes be feathered out with a repair mortar. Once the whole floor is out of true, though, or the level needs to come up evenly across a room, a self-levelling compound is the usual answer. A Floor Leveller is a cement- or gypsum-based powder mixed with water, or a latex additive, to a runny consistency, then poured across the prepared subfloor where it flows out, finds its own level and sets hard and flat.
Preparation makes or breaks it. The surface has to be clean, sound and free of dust, because the compound bonds to whatever is beneath it. Most subfloors need priming first. Primer stops a porous base sucking the water out of the mix too fast, which leaves a weak, powdery finish, and it stops a non-porous base such as old tile or a sealed screed from letting the compound slide around. Skipping the primer is the single most common reason a levelling job fails.
Mixing matters more than people expect. Follow the water ratio on the bag to the letter. Too much water and you weaken the compound and invite cracking and surface dust; too little and it will not flow properly, leaving you with trowel marks and high spots. Use a paddle on a drill, mix to a lump-free slurry, and only make up as much as you can pour and work within the pot life, which can be as little as fifteen to twenty minutes.
Pour in sections, working from the far corner back towards the door so you are never standing in wet compound. Spread it roughly with a trowel or a gauge rake to help it on its way, then run a spiked roller over the surface to knock out air bubbles. Wear spiked shoes if you need to walk across a fresh pour. Then leave it alone.
Drying times are where people trip at the last hurdle. A thin pour might take foot traffic in a few hours, but that is not the same as being ready for tiling or vinyl. Depending on the product, the thickness and the room’s humidity, you may need anything from overnight to several days, and moisture-sensitive floors such as wood or some vinyls need the slab properly dry underneath or they will fail later. Check the manufacturer’s figures and, if in doubt, test the moisture before you cover it over.
None of this is difficult, but it is unforgiving of shortcuts. A floor that has been levelled properly and given time to cure gives every finish above it a fair chance. Rush the base and no quality of tile or plank will save you.
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