How thick should self-levelling compound be for an uneven Calgary basement floor?

Most self-levelling compounds can be poured from a feathered edge (nearly zero) up to about 1 inch in a single pour, with the typical Calgary basement floor needing between 1/4 inch and 1/2 inch to achieve the flatness required for modern flooring. If you need more than 1 inch of levelling, you will need to either do multiple pours (allowing each layer to cure fully before the next) or use an extended-pour product designed for thicker applications, some of which can go up to 2 inches or more in a single lift.

The flatness tolerance you need to achieve depends on your flooring type. Floating floors (LVP, laminate, engineered hardwood) require the slab to be flat within 3mm over 1.8 metres — roughly 1/8 inch over 6 feet. Tile requires even tighter flatness, particularly with large-format tiles (24x24 inch and larger) where any subfloor irregularity causes lippage between tiles. Carpet is the most forgiving, but even carpet will telegraph significant humps and dips through the padding. Before pouring any compound, use a 6-foot straightedge to map the floor and identify the high and low spots. This tells you exactly how thick the pour needs to be and where.

Standard self-levelling compounds available at Calgary building supply stores include brands like Mapei Novoplan 2 Plus, Henry 555 Level Pro, and Ardex K-301. These products are designed to be mixed to a pourable consistency, dumped onto the floor, and spread — gravity does most of the work, as the compound naturally flows to fill low spots and create a level surface. At 1/4-inch thickness, material cost runs about $1.50 to $2.50 per square foot. At 1/2-inch thickness, figure $2.50 to $4.00 per square foot. At a full inch, you are looking at $4.00 to $6.00 per square foot just in material. Professional labour to prep the slab, prime it, mix, pour, and finish adds $2 to $4 per square foot.

Calgary-specific considerations for self-levelling compound. First, the slab must be clean and properly primed — most self-levelling compounds require a latex or acrylic primer to ensure a proper bond to the concrete. Paint, adhesive residue, or efflorescence (white mineral deposits common on Calgary basement slabs) must be removed or the compound will delaminate. Second, temperature matters — most products require the slab and room temperature to be between 10 and 30 degrees Celsius during pouring and curing. In a Calgary basement in January, the slab surface temperature may be below 10 degrees unless the home has been well heated for several days. Follow manufacturer requirements carefully. Third, conduct a moisture test before pouring — self-levelling compound over a slab with excessive moisture vapour emission can fail to cure properly or trap moisture beneath the finished floor.

For severely uneven Calgary basement floors — those with dips or humps exceeding 1 to 2 inches — self-levelling compound alone may not be the most cost-effective solution. At that level of unevenness, a plywood-over-sleeper subfloor system allows you to shim the sleepers to create a level surface while also adding insulation and a moisture barrier. Your flooring professional can help you determine which approach makes more sense for your specific situation. Find local flooring contractors through the Calgary Construction Network directory at calgaryconstructionnetwork.com/directory?trade=flooring.