Floor Levelling Compound vs Screed

What levelling compound is for

Self-levelling compound, often called latex, is poured thin, usually a few millimetres, to give a smooth, flat surface before vinyl, LVT, carpet or tiles. It fills small dips and covers rough patches.

When you need a screed instead

• The floor is out by more than the compound's maximum depth
• The floor slopes from room to room
• Underfloor heating is going in
• The old floor is cracked, crumbling or hollow

Prep is where most jobs fail

Compound only bonds to a clean, sound, primed surface. Dust, old adhesive, paint and loose patches all stop it sticking, and that's when it cracks or lifts. Prime first, every time.

Bonded and polymer modified screed

For floors in between, a bonded or polymer modified screed goes down thinner than a standard screed and bonds hard to the old concrete. That's often the fix for renovations where floor height is tight.

Prepping a floor for levelling compound

• Scrape off old adhesive, paint and anything loose
• Fill cracks and holes, and fix any hollow patches
• Vacuum up all the dust
• Prime the floor with the primer the compound maker recommends
• Seal doorways so the compound stays where you want it
• Mix the full bag to the right water amount and pour quickly

Why levelling compound cracks or lifts

• No primer, or the wrong primer
• Dust or old adhesive under it
• Poured thicker than the product allows
• Too much water in the mix
• A moving floor underneath, like loose boards or a hollow screed

Levelling a timber floor

Timber floors move, so they usually need overboarding with plywood and a flexible levelling compound made for timber. A standard compound poured straight onto old floorboards will crack.

DIY or get it done?

A small room with a few dips is a reasonable DIY job with the right compound. Big floors, deep dips, or a floor going under expensive tiles or timber are worth getting done properly. We do floor levelling jobs of any size, even a single room.

From JAM Floor Screeding, Portlaoise. Over 20 years laying screed across Leinster. Figures here are typical guidance; your floor's spec and the manufacturer's data sheet always come first.