How do I level an uneven basement floor in a New Brunswick home?

Levelling an uneven basement floor in a New Brunswick home depends on the cause and degree of the unevenness — self-levelling concrete underlayment handles minor irregularities up to about 1.5 inches, while significant settlement or structural heaving requires more involved repair before any floor work. Diagnosing the cause first saves you from investing in a fix that won't last.

Common causes of uneven basement floors in NB homes:

Slab settlement — portions of the floor have sunk due to soil consolidation or voids beneath the slab. This is common in older Fredericton, Saint John, and Moncton homes where the original fill beneath the slab has settled over decades.

Frost heave — sections of the slab have been lifted by frost acting on poorly drained soil beneath. This typically affects slabs with insufficient or no gravel base. The heaved sections may be higher than the surrounding floor.

Original pour variation — many older NB basement slabs were simply poured without careful screeding and have always been uneven. This is the easiest to fix.

Active moisture or drainage issues — if the unevenness is accompanied by moisture, the drainage problem must be solved before any levelling work.

Levelling Methods

Self-levelling compound (SLC): For depressions and low spots up to 1.5 inches, self-levelling underlayment is the most practical solution. Products like Ardex K-15 or Mapei Ultraplan flow into low areas and level themselves. They can be walked on in 2–4 hours and are ready for flooring in 24 hours. The concrete surface must be primed first. Cost is roughly $0.50–$1.50 per sq ft for materials; professional installation adds $2–$4 per sq ft.

Grinding high spots: If sections are raised above the general floor level (frost heave), a concrete grinder removes the high spots. Floor grinders are available at tool rental outlets in Moncton, Fredericton, and Saint John. Grinding is dusty work — use proper respiratory protection.

Mudjacking or poly levelling: If entire sections have settled significantly (2 inches or more), foam injection (poly levelling) through small holes drilled in the slab can lift settled sections back to level. Cost runs $3–$10 per sq ft depending on the extent of lifting required. This is professional work with specialized equipment.

Full slab replacement: For floors with extensive settlement, active frost heave, or major cracks, removing and replacing the slab is sometimes the only durable fix. This allows proper gravel base installation (6–8 inches compacted granular B) and a properly specified new slab.

For floors in NB homes older than 40 years, check whether the floor is adequately thick before grinding — older slabs sometimes are only 2–3 inches thick, leaving little room to remove material. New Brunswick Concrete can match you with local concrete professionals who can assess your floor and recommend the right levelling approach for your situation.