Flooring in Indus, Alberta

Indus project

Slab ground and levelled before vinyl plank

On a basement slab out here, the concrete decides what is possible, and a floating vinyl plank shows every hump and dip it sits over.

The slab is surveyed for flatness, moisture is recorded and cracks are looked at properly. High spots are ground down, low spots are filled with levelling compound, and anything that goes through the concrete is done first. The vinyl plank goes down once the surface meets the product’s flatness tolerance.

Pictured: our Indus project – light vinyl plank being laid across a levelled basement slab, with a shop vacuum and tools nearby.

See floor levelling

Expansive clay reaches the slab before it reaches the footings

Indus sits in open country close to Calgary's eastern edge, and the ground under this whole region is the reason basement floors get their own conversation.

Expansive, shrink-swell clay is widespread across Alberta. It takes on water and swells, dries out and contracts, and it does not do either evenly. What surprises most homeowners is that basement floor slabs move with it far more than footings do, which is why a heaved or cracked slab is a much more ordinary finding than foundation damage.

The practical consequence is that a basement can look entirely normal and still be out of flat by a noticeable amount from one corner to the other. It is also why we survey the whole slab plane rather than the room being finished. A slab does not stop moving at a partition wall that was framed on top of it.

Grinding, filling and the line item people overlook

Once the plane is mapped, the preparation splits into two jobs.

High points get ground back. Low areas get filled with self-levelling compound. Which of the two dominates depends on where the concrete has moved, and a large open area that has lifted in the middle often needs both. The quantity of compound is what makes this a real cost line, not a rounding error, and it is a common reason a floor quote changes after someone has looked at the slab.

Crack assessment runs alongside it but answers a different question. Width is less important than whether the two sides still sit level with each other. A tight, stable crack with no vertical offset is a preparation item and nothing more. A crack with a lip tells you something moved, and it narrows what can sensibly go over it. Rigid plank tolerates a little of this. Tile tolerates almost none.

We quote levelling as its own line for exactly that reason. Folded into a per-square-foot figure it becomes invisible, and invisible costs are the ones that turn into arguments.

Anything that penetrates the concrete happens first

The last part is sequencing, and it costs nothing except a conversation in the right week.

Health Canada's radon action level is 200 Bq/m3. Where a property tests at or above it, mitigation normally means work at the slab: a core for sub-slab depressurization, plus sealing of cracks, the sump lid and other openings. We do not test for radon and we do not install mitigation systems. What we can do is make sure that work, if it is coming, happens before the finished floor rather than after it.

The same logic covers drainage work, plumbing under the slab and any framing that has to be fastened through the concrete. Get everything that penetrates the slab finished, then floor it once. Cutting into a new floor to reach the concrete underneath is entirely avoidable.