What is self-levelling compound and when do I need it for NB flooring?

Self-levelling compound is a cementitious mixture that you pour over an uneven concrete or wood subfloor to create a flat, smooth surface for flooring installation. It flows out like thick pancake batter, finds its own level through gravity, and hardens into a stable, flat surface — typically within 4–24 hours depending on the product and thickness. In New Brunswick, where many homes have older concrete basement slabs and aging wood subfloors, self-levelling compound is one of the most commonly needed subfloor preparation steps.

You need self-levelling compound when your subfloor has dips, humps, or unevenness exceeding the tolerances required by your flooring product. Most flooring manufacturers specify that the subfloor must be flat to within 3/16 inch (about 5mm) over a 10-foot span. For rigid flooring like tile, the tolerance is even tighter — 1/8 inch over 10 feet. If your floor exceeds these tolerances, thin flooring materials like LVP, laminate, and especially tile will telegraph every imperfection, creating visible bumps, hollow spots that flex underfoot, and accelerated wear at high points.

In New Brunswick specifically, self-levelling compound is frequently needed in several common scenarios. Older NB homes built before the 1970s often have concrete basement slabs that were poured without modern screeding techniques, leaving uneven surfaces with 1/4 to 1/2 inch variation across a room. Homes in river valley communities like Fredericton and Miramichi may have experienced subtle foundation movement from spring flooding cycles, creating gradual slopes across basement floors. And NB's 100+ annual freeze-thaw cycles can shift pier foundations and crawl space structures, creating unevenness in ground-level wood subfloors that transfers to the floor above.

The process involves several steps. First, the subfloor must be clean, dry, and free of loose material. Any cracks wider than 1/4 inch should be filled first with a patching compound. A primer is applied to help the leveller bond to the substrate — this step is critical and should never be skipped. Then the compound is mixed to manufacturer specifications (proper water ratio is essential) and poured, starting at the far wall and working toward the exit. A gauge rake or smoother helps distribute the material evenly. Most products are walkable within 4–6 hours and ready for flooring within 24 hours for thin pours.

Self-levelling compound in NB typically costs $2–$4 per square foot applied professionally, including materials and labour. For a typical 400-square-foot basement, that is $800–$1,600 — a significant cost, but far cheaper than replacing flooring that fails because of an uneven subfloor. Materials alone run about $35–$50 per bag, and each bag covers roughly 40–50 square feet at 1/8 inch thickness.

A few important cautions for NB installations. Self-levelling compound adds weight to your floor — about 1.5 lbs per square foot per 1/8 inch of thickness. On wood subfloors, verify that your floor joists can handle the additional load before pouring. The compound also needs the room to be above 10°C during application and curing, which matters for unheated NB basements during the colder months. And while small pours in a singl room can be a DIY project, larger areas or pours exceeding 1/2 inch thickness are best left to a professional — the compound sets quickly, and once it starts hardening you cannot rework it. Getting matched with an experienced flooring installer who includes proper subfloor preparation in their scope of work will save you headaches down the road.

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Looking for experienced contractors? The New Brunswick Construction Network connects homeowners with qualified professionals:

• Arctic Fox Construction Inc.
• 3Tone Construction Ltd
• Forever Epoxy Inc
• The Garbage Guys Ltd
• RenoMe