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Finishes range from a quick seal on an existing slab to a multi-step polish, and the look depends heavily on how deep the grinding goes.

Every finish starts with preparation: old paint, glue and sealers are ground off, holes and cracks filled, and the surface opened up for the finish chosen. Polishing then works through finer and finer diamonds, with a densifier applied part way through and a stain-resistant guard at the end. Wet grinding keeps dust down but produces a slurry that has to be contained and disposed of properly, while dry grinding depends on powerful vacuum extraction.

Either way, grinding a slab releases crystalline silica, which the Canadian Centre for Occupational Health and Safety says can damage the lungs and lists as a known cause of lung cancer; it advises against dry sweeping and compressed air. In a lived-in house, ask for grinders connected to HEPA dust extractors, plastic sealing off the work area, heating vents and returns covered, and HEPA vacuuming at the end. In an older home, have black adhesive or old floor tile left on the slab tested before anyone grinds it, since Health Canada notes that asbestos fibres are released when such materials are sanded or removed.

New concrete cures and dries slowly, giving off moisture long after it hardens. Natural Resources Canada advises allowing about a year of drying time before insulating or renovating a new basement, and while a polish tolerates moisture better than a glued floor, stains, dyes and film-forming sealers each come with moisture and age requirements from their makers. When a new slab will be polished, the finishing, curing method and protection during construction are best planned from the day of the pour.

In older basements, moisture rising from the ground is the bigger question, especially where no vapour barrier was placed under the slab. White powdery deposits, damp patches, a musty smell and old sealers that whiten or peel all hint at it. Moisture carries salts that can blotch stains and cloud or lift topical sealers, so the installer should test the slab as the finish maker directs, and water coming through cracks or at the wall joint gets fixed before any finish goes down.

Concrete conducts and stores heat well, which makes a polished or stained slab one of the best finishes over in-floor heating, with no wood or rug slowing the warmth. Hydronic tubing is cast into the slab during the pour, so the heating design is settled before the concrete arrives, and grinding an existing heated slab is kept shallow and planned around the tubing's depth. Designing the system and connecting it to a boiler or heat pump is work for a heating contractor, as the in-floor heating page explains.

Without heat, a bare basement slab feels cold underfoot. Natural Resources Canada notes that basement slabs are seldom insulated because most heat is lost through the upper part of the foundation walls, and calls installing or replacing a slab an excellent opportunity to add in-floor heating or make the floor radiant-ready, with insulation and heating lines placed before the pour. An existing slab kept as the finished floor can't be insulated underneath without replacing it, so comfort comes from rugs on breathable pads, good heating and steady humidity.

Nearly every slab has cracks, and a polished or stained finish shows them rather than hiding them. Fine shrinkage cracks and saw-cut control joints are usually filled with a flexible or semi-rigid filler, tinted to blend in or left to contrast, and many owners come to see them as character. Patches and filled cracks take stain and polish differently from the original concrete, so they'll always read as repairs.

Cracks that are wide, growing, offset from one side to the other or letting water in aren't a finishing issue. They point to settlement, frost, drainage or structural movement, covered on the concrete repair and foundation cracks pages, and should be diagnosed before money goes into a finish. A slab that's badly cracked, heavily patched or far out of flat is often better covered with another floor or a decorative overlay than polished.