Basement floor repair

Because there is an air gap under the floor at that spot, and over a slab the concrete is usually the reason. Basement slabs are rarely poured dead flat, and dips around a floor drain, along a settlement crack, or where a section of slab has sunk leave a void that the flooring bridges. In a raised panel or sleeper system, a panel rocking on a high point of the concrete or a sleeper that has bowed with moisture does the same thing. The repair is made underneath: low areas filled with levelling compound, or the panel or sleeper shimmed and refastened, before the affected flooring goes back down.

It can be, and it is worth checking properly rather than treating it as an air-freshener problem. Moisture moving up through a concrete slab can be held against the underside of the flooring where it cannot evaporate, and a musty odour is often the first sign of that, well before anything is visible on the surface. Finding out where the moisture is coming from matters more than the flooring. Natural Resources Canada notes that a dry slab helps limit mould, water damage and musty odours.

It is the white, powdery mineral deposit you sometimes see on concrete, left behind when moisture moves through the slab and evaporates at the surface, carrying dissolved salts with it. The deposit itself is harmless. What it tells you is not: it is direct evidence that moisture is moving up through your slab, which is worth understanding before putting flooring over it.

Solid hardwood is not made for below-grade concrete. Makers such as Mullican limit solid wood flooring to on-grade and upstairs floors, because concrete holds moisture and passes it to the wood. Engineered hardwood, luxury vinyl plank and laminate over a vapour barrier suit below-grade conditions better. Putting a new floor in is a job for a flooring installer; what we do is repair the flooring already there. If you already have solid hardwood down there and it is cupping, the slab's moisture is the first thing to check.

Often. In many older houses the slab was poured with nothing between the concrete and the soil, so moisture from the ground has a direct path up. Some of those slabs stay dry and others pass moisture continuously, and the age of the house alone does not tell you which. That is why we test the slab rather than assume, before recommending a repair.

Not necessarily. Warm, humid summer air can condense on a cool basement slab, which looks like ground moisture but is not. The plastic-sheet test separates the two: moisture under the sheet is coming up from the ground, moisture on top is from the room air. Room-air moisture is handled with a dehumidifier, which Health Canada suggests running in a basement where needed. Ground moisture needs a vapour barrier or membrane under the new floor, and water coming through cracks needs a waterproofing contractor.