How do we deal with a slightly uneven concrete floor before installing flooring?

A slightly uneven concrete basement floor can absolutely be leveled before installing your flooring, and addressing it properly will ensure your new floors look professional and last longer. The approach depends on how uneven we're talking about and what type of flooring you're planning to install.

For minor variations (less than 1/4 inch over 10 feet), you have several effective options. Self-leveling compound is often the go-to solution - it's a cement-based product that flows and settles to create a smooth, level surface. In Ottawa's climate, you'll want to ensure the basement is properly heated (ideally 65-70°F) during application and curing, especially during our colder months. The compound typically costs $2-4 per square foot for materials, plus labor if you're hiring professionals.

Grinding down high spots is another approach for minor unevenness. A concrete grinder can remove high areas, though this creates dust and requires proper ventilation and cleanup. This works well when you have isolated bumps or ridges rather than widespread dips.

For moderate unevenness (1/4 to 1/2 inch variations), you might need a combination approach. Start by grinding high spots, then use self-leveling compound to fill the remaining low areas. Some flooring types are more forgiving - luxury vinyl plank (LVP) can handle minor imperfections better than ceramic tile, which requires a perfectly flat substrate.

Ottawa-specific considerations include our freeze-thaw cycles, which can cause concrete movement over time. Before leveling, check for any cracks or signs of moisture intrusion - these need addressing first. Ontario Building Code requires proper vapor barriers under most basement flooring, so factor this into your leveling strategy.

Professional guidance becomes important when variations exceed 1/2 inch or when you're dealing with structural issues causing the unevenness. Licensed contractors can assess whether the problem stems from foundation settling, poor original pour, or other structural concerns that need addressing before cosmetic fixes.

Safety considerations include proper ventilation when using chemical-based leveling compounds, and ensuring adequate moisture testing before proceeding. Basement concrete should have moisture levels below 4.5% for most flooring installations.

Next steps: First, use a long straight edge or laser level to map exactly where and how much your floor varies. Take photos and measurements - this helps contractors provide accurate estimates and determines if this is a DIY project or requires professional intervention. For significant unevenness or if you're installing expensive flooring, getting a professional assessment ensures you don't end up with costly callbacks later.