Subfloor Prep — Self-Leveling Compound & Patch
A flat subfloor is the part of a flooring install nobody sees and everybody notices when it’s skipped — dips and ridges telegraph through laminate and vinyl, and can leave engineered or solid hardwood squeaking or gapping over time. Before any new floor goes down, the existing subfloor needs to be within the flooring manufacturer’s allowable flatness tolerance, and that usually means either a targeted patch or a full self-leveling pour.
We stock both ends of that job: Ardex Feather Finish and Ardex GPS for smaller gouges, seams and low spots that just need a trowel and a bit of feathering, and Ardex K 15 or Custom LevelQuik ES for a subfloor that’s sloped or uneven across a larger area and needs a full self-leveling pour. Concrete subfloors need a compatible primer first in almost every case — it’s the step that gets skipped most often and the one most likely to cause a leveler to fail. The decision table below is the short version of which product fits which job.
Patch compound vs. self-leveling pour
| Subfloor condition | Use |
|---|---|
| Small gouges, seams, isolated dips | Ardex Feather Finish or Ardex GPS (trowel-applied patch) |
| Sloped or uneven across a large area | Ardex K 15 or Custom LevelQuik ES (self-leveling pour) |
| Bare concrete before any leveler above | Ardex P 51 primer first |
| Need more working time for a DIY pour | Custom LevelQuik ES (extended setting) |
| Fastest re-cover for a small patch | Ardex Feather Finish (flooring in as fast as 15–20 min) |
Free pickup in Markham (ready next business day) · GTA delivery $140
Subfloor Prep
Self-levelling underlayment and patch/skimcoat compounds, sold per bag.
Premium self-leveller that flattens uneven slabs before any floor goes down, covering about 50 sq ft per 55 lb bag.
1 bag covers ~50 sqft → 500 sqft needs 10 bags
Self-leveling underlayment for smoothing subfloors before flooring installation, available in extended-set for larger pours and rapid-set for faster turnaround.
1 bag covers ~50 sqft → 500 sqft needs 10 bags
Cement-based skim coat for feathering seams and low spots to zero before flooring goes down. Available in gray or white, 10 lb bags.
Fast-setting patch for holes, cracks and plywood seams, packed in a 25 lb bag.
Premium self-leveling underlayment for flattening subfloors ahead of any flooring install, gray, 50 lb bag.
High-flow, reactivatable self-leveller for flattening subfloors, gray, 50 lb bag.
High-flow, fiber-reinforced self-leveller for flattening subfloors, gray, 50 lb bag.
A self-leveling underlayment for evening out subfloors before flooring installation, sold in a 50 lb bag.
A gray self-leveling underlayment for creating a smooth, even subfloor surface ahead of finish flooring.
A self-leveling underlayment for interior wood and concrete subfloors, gray finish. Use it to smooth out uneven floors before final flooring goes down.
Rapid-setting latex smoothing and leveling compound kit for subfloor prep.
A fiber-reinforced self-leveling underlayment built specifically for wood subfloors, adding strength where plywood or OSB needs extra support.
A self-leveling underlayment for smoothing and flattening subfloors ahead of flooring installation.
A professional self-levelling underlayment for smoothing subfloors before installing finish flooring.
A self-leveling underlayment for smoothing and flattening concrete or wood subfloors before installing your finish flooring. Sold in a 50 lb bag.
A high-flow self-leveling compound that spreads easily to flatten concrete and wood subfloors ahead of flooring installation. Comes in a 50 lb bag.
A deep-pour self-levelling compound for correcting subfloors with larger low spots that need more depth than a standard leveler.
A high-performance, quick-setting self-leveling underlayment for flattening subfloors before flooring installation. Sold in a 50 lb bag.
A quick-setting self-leveling underlayment for flattening and preparing subfloors before flooring goes down. Sold in a 50 lb bag.
A polymer-modified, hi-flow self-leveling underlayment that fills and flattens subfloors ahead of flooring installation. Sold in a 50 lb bag.
A self-leveling underlayment for flattening and smoothing subfloors before installing any flooring type. Sold in a 50 lb bag.
Cement-based self-leveling underlayment used to flatten and smooth concrete or plywood subfloors before flooring installation, packaged in a 50 lb bag.
A self-levelling underlayment that fills low spots and evens out concrete or wood subfloors before you install your finish flooring.
Self-drying finishing underlayment for smoothing subfloors, sold in a 10 lb bag.
A gray skimcoat compound for patching and finishing subfloor surfaces before final flooring installation.
A moisture-resistant, rapid-drying skimcoat for patching and smoothing subfloor imperfections, gray finish. Good for small repairs and touch-ups before install.
A trowelable, self-drying underlayment for concrete subfloors, gray finish, in standard and Rapid formulas so you can match dry time to your schedule.
A fast-setting, polymer-modified cement-based patch for filling cracks, holes and low spots in concrete and wood subfloors. Available in 4.4 lb, 10 lb and 22 lb bags.
A fiber-reinforced skimcoating compound for smoothing textured or uneven subfloors before flooring goes down. Comes in a 10 lb bag.
A floor patching compound for repairing and smoothing subfloor surfaces before installation. Available in 10 lb and 20 lb bags.
A high-performance patching compound for repairing and filling concrete subfloors before flooring goes down.
A subfloor patching compound for filling and repairing imperfections before flooring installation. Sold in a 25 lb bag.
A patching compound for filling low spots, cracks and holes in subfloors before installing new flooring.
A fast drying patching compound for filling small dips, cracks and holes in a subfloor before installation.
A skim coat compound for smoothing minor subfloor imperfections before flooring goes down. Sold in a 10 lb bag.
A fine, calibrated mesh sand used as an additive with self-levelling and patching compounds for deeper pours.
A 23-1/4 by 23-1/4 inch subfloor panel for laminate and vinyl installs, available in a 19 mm Air Plus version and a 25 mm insulated version.
How-to guides
FAQ
Do I need to level my subfloor before installing new flooring?
Most flooring manufacturers specify a maximum allowable dip — commonly around 3/16" over a 10-foot span, though this varies by product, so check your flooring’s installation instructions. If your subfloor has low spots, humps, or an old adhesive residue pattern beyond that, levelling it first prevents dips telegraphing through the new floor and voiding the warranty.
Patch compound or full self-leveling pour — which do I need?
Small gouges, seams, and isolated low spots are a job for a patch/skimcoat compound like Ardex Feather Finish or Ardex GPS — quick, trowel-applied, no mixing equipment needed. A subfloor that’s sloped or uneven across a large area needs a self-leveling underlayment (Ardex K 15 or Custom LevelQuik ES) that pours and finds its own level.
Do I need to prime before pouring a self-leveler?
On concrete, yes — nearly every self-leveling underlayment manufacturer requires a compatible primer first (Ardex P 51 for Ardex K 15) so the leveler doesn’t dry too fast at the surface and lose its bond to the slab. Skipping this step is one of the most common reasons a self-leveler cracks or delaminates.
How thick can I pour a self-leveler in one shot?
Ardex K 15 levels up to about 1/4" per pour and can be tapered at the edges to meet existing elevations. Custom LevelQuik ES (the "Extended Setting" formula) can be poured up to about 1.5" thick in one shot, and gives you more working time before it sets — useful for a larger room or a DIY pour without a pump.
How long before I can install flooring over a self-leveler or patch compound?
It depends on the product and your new floor covering — Ardex Feather Finish can be ready for flooring in as fast as 15–20 minutes since it’s self-drying, while a full self-leveling pour typically needs several hours to walk on and up to 16 hours before installing most floor coverings. Always check the bag for the exact schedule on the day you pour.