Concrete subfloor preparation is the most critical step in any GTA flooring installation — and the one most often skipped by eager renovators. A poorly prepared concrete slab will cause vinyl plank to lift, laminate joints to swell, and hardwood to cup within months. Here is how to do it right the first time.
Top Floorings Depot (3781 Victoria Park Avenue, Unit 1, Toronto) carries all the flooring options that work over concrete — from SPC vinyl starting at $1.39/sqft to European Oak engineered hardwood from $3.69/sqft. We serve homeowners and contractors across Scarborough, Mississauga, Brampton, North York, and the broader GTA.
How Do You Prepare a Concrete Subfloor for Flooring in a GTA Home?
Preparing a concrete subfloor for flooring installation requires five steps: moisture testing, crack repair, surface leveling, cleaning, and — where needed — vapour barrier installation. Skipping or short-cutting any of these steps is the primary reason floors fail in GTA basements and slab-on-grade renovations.
The Ontario Building Code sets minimum standards for floor deflection under finish flooring materials (Sentence 9.30.2.1), but it does not dictate surface preparation — that responsibility falls to the flooring contractor or the DIY homeowner. Top Floorings Depot recommends treating every concrete slab as potentially moist until testing proves otherwise, regardless of the home's age.
Start by clearing the space entirely. Remove all furniture, appliances, existing flooring, and any adhesive residue. Use a floor scraper or orbital scarifier for old adhesive — especially critical under vinyl plank, where adhesive bumps can telegraph through and cause joint failure. Finally, sweep and vacuum the bare slab. Dust and debris prevent proper bonding of leveler compounds and can puncture vapour barrier film.
What Moisture Level Is Safe to Install Over a Concrete Slab?
All new and existing concrete slabs must be moisture-tested before any flooring is installed over them. Concrete retains water from the pour and continues curing — and in GTA homes built on clay-heavy York Region soil, groundwater can migrate upward through the slab by capillary action.
The two accepted test methods are the Calcium Chloride (CaCl) test and the Relative Humidity (RH) probe test. The CaCl test measures moisture vapour emission rate in pounds per 1,000 square feet per 24 hours. The RH probe measures relative humidity within the concrete itself using a sensor inserted to 40% depth of the slab.
| Test Method | Maximum Reading | What It Tells You |
|---|---|---|
| Calcium Chloride (CaCl) | 3 lbs / 1,000 sqft / 24 hrs | Moisture vapour emission rate |
| RH Probe (in-situ) | 75% RH | Internal concrete moisture content |
If either test exceeds its threshold, you must address the moisture before installing flooring. Options include a standalone vapour barrier over the concrete, a moisture-resistant flooring product with an attached pad and integral vapour block, or professional drying of the slab. SPC vinyl plank from our Riche collection includes an attached IXPE or EVA pad on most lines — which adds a secondary moisture barrier — but a separate 6-mil polyethylene sheet is still recommended on below-grade slabs and in Scarborough and Mississauga homes with high water tables.
Do You Need a Vapour Barrier Over Concrete Before Vinyl Plank?
For SPC vinyl plank with an attached pad, a separate vapour barrier is not always required — but it is almost always recommended in the GTA. The reason: the attached pad on most SPC products (including all Riche Flooring lines) is an comfort and sound-dampening layer, not a moisture barrier. The rigid SPC core resists water, but moisture migrating up through the concrete can still degrade the edges and subfloor connection over time.
Install a 6-mil polyethylene vapour barrier over any concrete slab where the CaCl test reads above 2 lbs or where the slab is below grade (most GTA basements). Lap the sheets 6 to 8 inches, tape the seams, and run the film 2 inches up all walls — this creates a complete moisture envelope. For floors that test clean (under 2 lbs CaCl), the vapour barrier remains optional but is still low-cost insurance.
Laminate flooring always requires a separate vapour barrier over concrete — the core swells on contact with moisture. Swiss Krono Grey Oak 10mm AC5 laminate from $0.70/sqft is a solid choice for concrete subfloors, and it pairs with any standard 6-mil vapour barrier film.
How Do You Repair Cracks and Uneven Concrete Before Flooring Installation?
Hairline cracks up to 1/8 inch wide in concrete are cosmetic and generally do not affect flooring installation — but anything wider needs to be filled to prevent moisture ingress and, in the case of rigid SPC vinyl, to prevent the crack from telegraphing through the plank joints.
For cracks 1/8 to 1/4 inch wide, use a concrete epoxy crack injection kit. These two-part epoxies penetrate the crack and bond to the concrete on both sides, creating a structural repair. For cracks wider than 1/4 inch, or for any crack showing vertical movement (one side higher than the other), call a concrete contractor first — vertical displacement signals possible structural movement that no epoxy will fix.
Uneven concrete is more common than cracking in GTA homes. Slabs poured in the 1960s through 1990s — common in older Scarborough, Etobicoke, and North York bungalows — frequently have 1/4 to 1/2 inch dips over 10-foot runs. For deviations under 3/16 inch over 10 feet, a self-leveling compound (SLC) is the solution. Apply a primer coat first (MAPEI Primer L is widely available at Canadian Tire), then pour the SLC in sections and let it cure for 24 to 48 hours before proceeding.
High spots — bulges in the concrete — should be ground flat with a floor grinder before the SLC is poured. Expansion joints in the concrete (marked by pre-formed compressible strips) must always remain open and uncovered. Flooring over an expansion joint without a transition strip will crack the floor when the concrete contracts in winter.
Our Top Picks at Top Floorings Depot
These products are specifically suited for installation over concrete subfloors in GTA homes:
- Riche Truffle Brown Oak 6mm SPC Vinyl Plank — 6mm total thickness (4.5mm core + 1.5mm IXPE pad), 12mil wear layer, 7.09-inch width, click-lock with UniPush system. $1.64/sqft. Warm medium-brown oak tone ideal for main floor living areas with concrete subfloors.
- Riche Sandstone Oak 9mm SPC Vinyl Plank — 9mm total thickness (7mm core + 2mm EVA pad), 12mil wear layer, 5.9-inch width, Valinge 5G Drop Lock. $1.85/sqft. The thicker core and EVA pad make this the better choice for uneven concrete subfloors in basement apartments — the extra padding bridges minor subfloor imperfections.
- Riche Natural Birch 6mm SPC Vinyl Plank — same 6mm spec as the Truffle Brown, light natural birch colour. $1.64/sqft. Best for north-facing GTA rooms where a lighter floor helps reflect available light.
- Swiss Krono Grey Oak 10mm AC5 Laminate — 10mm thickness, AC5 commercial grade, Valinge locking system, grey oak tone. $0.70/sqft. Install over concrete with a 6-mil vapour barrier — the AC5 rating handles heavy residential and light commercial foot traffic.
All four products are in stock at our Victoria Park showroom and available for same-day pickup or GTA-wide delivery.
Preparing Your Subfloor Is the Step That Determines Everything
No flooring product — regardless of price or quality — will perform well over a poorly prepared concrete subfloor. Moisture, cracks, and uneven surfaces are the three enemies of every floor installed over concrete in the GTA. Test first, repair cracks, level the surface, install a vapour barrier where needed, and you will have a floor that lasts.
Have questions about whether your concrete slab is ready for new flooring? Bring a photo and the measurements to our showroom at 3781 Victoria Park Avenue, Unit 1, Toronto, or call us at 416-499-0117. We are open Monday to Friday 9–5:30 and Saturday 9–4.
## Visit Top Floorings Depot **Top Floorings Depot** 3781 Victoria Park Avenue, Unit 1, Toronto, ON M1W 3K5 www.topfloorings.com Call 416-499-0117 | Text 416-770-8819 **Showroom Hours:** Monday–Friday 9–5:30 | Saturday 9–4 | Sunday Closed We serve homeowners and contractors across Toronto, Scarborough, Mississauga, Brampton, and North York. Visit our showroom to see and feel these products in person, or contact us for contractor pricing and bulk orders. GTA-wide delivery available. Follow us on Instagram: @topflooringsdepotgta